Let us now imagine what degree of transparency of air is admitted by its molecular constituents, viz.
In 1831, from a study of the specific heats of compounds, he formulated "Neumann's law," which expressed in modern language runs: "The molecular heat of a compound is equal to the sum of the atomic heats of its constituents."
This oxide exists in two forms. The aform is readily fusible and melts at 14.8° C. It corresponds to the simple molecular complex S03.
In such experiments the molecular energy of a gas is converted into work only in virtue of the molecules being separated into classes in which their velocities are different, and these classes then allowed to act upon one another through the intervention of a suitable heat-engine.
It corresponds to the molecular complex (S03)2.
Hantzsch (Ber., 1901, 34, p. 3337) has shown that in the action of alcohols on diazonium salts an increase in the molecular weight of the alcohol and an accumulation of negative groups in the aromatic nucleus lead to a diminution in the yield of the ether produced and to the production of a secondary reaction, resulting in the formation of a certain amount of an aromatic hydrocarbon.
In 1894 and 1895, Fischer, in a remarkable series of papers on the influence of molecular structure upon the action of the enzyme, showed that various species of yeast behave very differently towards solutions of sugars.
The alkyl derivatives may be obtained by heating phenol with one molecular proportion of a caustic alkali and of an alkyl iodide.
He held that every fermentation consisted of molecular motion which is transmitted from a substance in a state of chemical motion - that is, of decomposition - to other substances, the elements of which are loosely held together.
The extent of the area affected and of the variation in the turgor depends upon many circumstances, but we have no doubt that in the process of modifying its own permeability by some molecular change we have the counterpart of muscular contractibility.
Deviation from this rule indicates molecular dissociation or association.
When we can build at the molecular level, we can build things I cannot imagine today.
isomerism, or the existence of two or more chemically different substances having identical molecular weights, is adequately shown; and, most important of all, once the structure is determined, the synthesis of the compound is but a matter of time.
The molecular weight determinations of W.
With Sydney Young and others he investigated the critical state and properties of liquids and the relationship between their vapour pressures and temperature, and with John Shields he applied measurements of the surface tension of liquids to the determination of their molecular complexity.
We will discuss the molecular machines called nanites—tiny, molecular-sized robots that will swim around in your body fighting disease, repairing damage, and alerting you to problems (and will likely dramatically increase the human lifespan).
In place of the relative molecular weights, attention was concentrated on relative atomic or equivalent weights.
Kopp systematized the earlier observations, and, having made many others, he was able to show that the molecular heat was an additive property, i.e.
He introduced the idea of comparing the refractivity of equimolecular quantities of different substances by multiplying the function (n-1)/d by the molecular weight (M) of the substance, and investigated the relations of chemical grouping to refractivity.
compounds having the same composition, have equal molecular refractions, and that equal differences in composition are associated with equal differences in refractive power.
Gerhardt found that reactions could be best followed if one assumed the molecular weight of an element or compound to be that weight which occupied the same volume as two unit weights of hydrogen, and this assumption led him to double the equivalents accepted by Gmelin, making H= 1, 0 =16, and C = 12, thereby agreeing with Berzelius, and also to halve the values given by Berzelius to many metals.
Thus, the symbols 14 2 and P4 indicate that the molecules of hydrogen and phosphorus respectively contain 2 and 4 atoms. Since, according to the molecular theory, in all cases of chemical change the action is between molecules, such symbols as these ought always to be employed.
Chemistry and physics, however, meet on common ground in a well-defined branch of science, named physical chemistry, which is primarily concerned with the correlation of physical properties and chemical composition, and, more generally, with the elucidation of natural phenomena on the molecular theory.
From a study of the free elements Cannizzaro showed that an element may have more than one molecular weight; for example, the molecular weight of sulphur varied with the temperature.
they appear to differ in character; but if they are correctly represented by molecular equations, or equations which express the relative number of molecules which enter into reaction and which result from the reaction, it will be obvious that the character of the reaction is substantially the same in both cases, and that both are instances of the occurrence of what is ordinarily termed double decomposition H2 + C12 = 2HC1 Hydrogen.
This view was modified by Liebig, who regarded ether as ethyl oxide, and alcohol as the hydrate of ethyl oxide; here, however, he was in error, for he attributed to alcohol a molecular weight double its true value.
He also postulated, with Regnault, the existence of " molecular or mechanical types " containing substances which, although having the same number of equivalents, are essentially different in characters.
The first set provides evidence as to the molecular weight of a substance: these are termed " colligative properties."
In any attempts to gain an insight into the relations between the physical properties and chemical composition of substances, the fact must never be ignored that a comparison can only be made when the particular property under consideration is determined under strictly comparable conditions, in other words, when the molecular states of the substances experimented upon are identical.
When this is done, such densities are measures of the molecular weights of the substances in question.
Recent researches have shown that the law originally proposed by Kopp - " That the specific volume of a liquid compound (molecular volume) at its boiling-point is equal to the sum of the specific volumes of its constituents (atomic volumes), and that every element has a definite atomic value in its compounds " - is by no means exact, for isomers have different specific volumes, and the volume for an increment of CH 2 in different homologous series is by no means constant; for example, the difference among the esters of the fatty acids is about 57, whereas for the aliphatic aldehydes it is 49.
We may therefore conclude that the molecular volume depends more upon the internal structure of the molecule than its empirical content.
The molecular volume is additive in certain cases, in particular of analogous compounds of simple constitution.
Schroeder the silver salts of the fatty acids exhibit additive relations; an increase in the molecule of CH2 causes an increase in the molecular volume of about 15'3.
From the ratio Cp/C„ conclusions may be drawn as to the molecular condition of the gas.
Regnault confirmed Neumann's observations, and showed that the molecular heat depended on the number of atoms present, equiatomic compounds having the same molecular heat.
The molecular formula of a compound, however, is always a simple multiple of the empirical formula, if not identical with it; thus, the empirical formula of acetic acid is CH 2 O, and its molecular formula is C2H402, or twiceTCH 2 O.
the molecular weights were the same as in use to-day.) This connecting link, C2, was regarded as essential, while the methyl, ethyl, &c. was but a sort of appendage; but Kolbe could not clearly conceive the manner of copulation.
These bands are due to molecular oscillations; Hartley suggests the carbon atoms to be rotating and forming alternately single and double linkages, the formation of three double links giving three bands, and of three single links another three; Baly and Collie, on the other hand, suggest the making and breaking of links between adjacent atoms, pointing out that there are seven combinations of one, two and three pairs of carbon atoms in the benzene molecule.
It is found that isomers have nearly the same critical volume, and that equal differences in molecular content occasion equal differences in critical volume.
Kopp, begun in 1842, on the molecular volumes, the volume occupied by one gramme molecular weight of a substance, of liquids measured at their boiling-point under atmospheric pressure, brought to light a series of additive relations which, in the case of carbon compounds, render it possible to predict, in some measure, the cornposition of the substance.
In practice it is generally more convenient to determine the density, the molecular volume being then obtained by dividing the molecular weight of the substance by the density.
These values hold fairly well when compared with the experimental values determined from other compounds, and also with the molecular volumes of the elements themselves.
456) has given the formula Cp=6.5--aT, where a is a constant depending on the complexity of the molecule, as an expression for the molecular heat at constant pressure at any temperature T (reckoned on the absolute scale).
We now proceed to discuss molecular heats of compounds, that is, the product of the molecular weight into the specific heat.
Similarly, by taking the difference of the molecular heats of compounds differing by one constituent, the molecular (or atomic) heat of this constituent is directly obtained.
It may he shown theoretically that the absolute boiling-point is proportional to the molecular volume, and, since this property is additive, the boiling-point should also be additive.
These relations have been more thoroughly tested in the case of organic compounds, and the results obtained agree in some measure with the deductions from molecular volumes.
Mag., 18 93 [5), 35, p. 45 8) has shown that, while an increase in molecular weight is generally associated with a rise in the boiling-point, yet the symmetry of the resulting molecule may exert such a lowering effect that the final result is a diminution in the boiling-point.
The series H 2 S = - 61°, CH 3 SH = 21 °, (C 11 3) 2 S=41 ° is an example; in the first case, the molecular weight is increased and the symmetry diminished, the increase of boiling-point being 82°; in the second case the molecular weight is again increased but the molecule assumes a more symmetrical configuration, hence the comparatively slight increase of 20°.
Although establishing certain general relations between atomic and molecular refractions, the results were somewhat vitiated by the inadequacy of the empirical function which he employed, since it was by no means a constant which depended only on the actual composition of the substance and was independent of its physical condition.
This is shown in the following table (the values are for Ha) Additive relations undoubtedly exist, but many discrepancies occur which may be assigned, as in the case of molecular volumes, to differences in constitution.
Atomic refractions may be obtained either directly, by investigating the various elements, or indirectly, by considering differences in the molecular refractions of related compounds.
By subtracting the value for CH 2, which may be derived from two substances belonging to the same homologous series, from the molecular refraction of methane, CH 4, the value of hydrogen is obtained; subtracting this from CH 2, the value of carbon is determined.
Hydroxylic oxygen is obtained by subtracting the molecular refractions of acetic acid and acetaldehyde.
A table of the atomic refractions and dispersions of the principal elements is here given: Dispersion and Composition.-In the preceding section we have seen that substances possess a definite molecular (or atomic) refraction for light of particular wave-length; the difference between the refractions for any two rays is known as the molecular (or atomic) dispersion.
Since molecular refractions are independent of temperature and of the state of aggregation, it follows that molecular dispersions must be also independent of these conditions; and hence quantitative measurements should give an indication as to the chemical composition of substances.
We may here notice an empirical rule formulated by Nietzski in 1879: - the simplest colouring substances are in the greenish-yellow and yellow, and with increasing molecular weight the colour passes into orange, red, violet, blue and green.
It may be generally inferred that an increase in molecular weight is accompanied by a change in colour in the direction of the violet.
Hydrocarbons of similar structure have been prepared by Thiele, for example, the orange-yellow tetraphenyl-para-xylylene, which is obtained by boiling the bromide C6H4[CBr(C6H5)2]2 with benzene and molecular silver.
(3) If a colourless compound gives a coloured one on solution or by salt-formation, the production of colour may be explained as a particular form of ionization (Baeyer), or by a molecular rearrangement (Hantzsch).
Mendeleeff endeavoured to obtain a connexion between surface energy and constitution; more successful were the investigations of Schiff, who found that the " molecular surface tension," which he defined as the surface tension divided by the weight.
molecular weight, is constant for isomers, and that two atoms of hydrogen were equal to one of carbon, three to one of oxygen, and seven to one of chlorine; but these ratios were by no means constant, and afforded practically no criteria as to the molecular weight of any substance.
2 7, p. 45 2), assuming that two liquids may be compared when the ratios of the volumes of the liquids to the volumes of the saturated vapours are the same, deduced that yV 3 (where y is the surface tension, and V the molecular volume of the liquid) causes all liquids to have the same temperature coefficients.
Soc. 63, p. 1089; 65, p. 167), whose results have thrown considerable light on the subject of the molecular complexity of liquids.
Obviously equimolecular surfaces are given by (Mv) 3, where M is the molecular weight of the substance, for equimolecular volumes are Mv, and corresponding surfaces the two-thirds power of this.
Now the value of K, -y being measured in dynes and M being the molecular weight of the substance as a gas, is in general 2.121; this value is never exceeded, but in many cases it is less.
In order to permit a comparison of crystal forms, from which we hope to gain an insight into the prevailing molecular conditions, it is necessary that some unit of crystal dimensions must be chosen.
To reduce these figures to a common standard, so that the volumes shall contain equal numbers of molecules, the notion of molecular volumes is introduced, the arbitrary values of the crystallographic axes (a, b, c) being replaced by the topic parameters' (x, ?i, w), which are such that, combined with the axial angles, they enclose volumes which contain equal numbers of molecules.
Kryst., 1894), in his researches on the tetragonal potassium and ammonium dihydrogen phosphates and arsenates, found that the replacement of potassium by ammonium was attended by an increase of about six units in the molecular volume, and of phosphorus by arsenic by about 4.6 units.
Chloraloxime, CC1 3 CH: NOH, is obtained when one molecular proportion of chloral hydrate is warmed with four molecular proportions of hydroxylamine hydrochloride and a little water.
It crystallizes in prisms which melt at 39° C. A chloral hydroxylamine, CC1 3 [[Choh Nhoh]], melting at 98° C. is obtained by allowing a mixture of one molecular proportion of chloral hydrate with two molecular proportions of hydroxylamine hydrochloride and one of sodium carbonate to stand for some time in a desiccator.
18.14%, S=0.96%, O = 22.66%, which points to the formula C720H1134N218S50241, corresponding to the molecular weight 16,954.
A high molecular weight characterizes these substances, but so far no definite value has been determined by either physical or chemical means; A.
For instance, to take the two solutions to which we have already referred, we have of ions between molecules at the instants of molecular collision only; during the rest of the life of the ions they were regarded as linked to each other to form electrically neutral molecules.
In 1887 Svante Arrhenius, professor of physics at Stockholm, put forward a new theory which supposed that the freedom of the opposite ions from each other was not a mere momentary freedom at the instants of molecular collision, but a more or less permanent freedom, the ions moving independently of each other through the liquid.
Molecular Depressions of the Freezing Point.
The evidence in favour of dissociation in the case of solutions does not apply to fused salts, and it is possible that, in their case, a series of molecular interchanges, somewhat like Grotthus's chain, may represent the mechanism of conduction.
If µ be the molecular conductivity, and its value at infinite dilution, the fractional number of molecules dissociated is k /µop, which we may write as a.
a V(I - a) This constant k gives a numerical value for the chemical affinity, and the equation should represent the effect of dilution on the molecular conductivity of binary electrolytes.
The equation then becomes a 2 /V = k, or a = A / Vk, so that the molecular conductivity is proportional to the square root of the dilution.
According to the molecular theory, diffusion is due to the motion of the molecules of the dissolved substance through the liquid.
Under certain conditions, as when latex is allowed to stand or is centrifugalized, a cream is obtained consisting of the liquid globules, which may be washed free from proteid without change, but, either by mechanical agitation or by the addition of acid or other chemical agent, the liquid gradually solidifies to a mass of solid caoutchouc. The phenomenon therefore resembles the change known to the chemist as polymerization, by which through molecular aggregation a liquid may pass into a solid without change in its empirical composition.
The properties of caoutchouc clearly show, however, that its actual molecular structure is considerably more complex than is represented by the empirical formula, and that it is to be regarded as the polymer of a terpene or similar hydrocarbon and composed of a cluster of at least ten or twenty molecules of the formula C5H8.
The exact chemical nature of caoutchouc is, however, not determined, and recent researches point to the view that its molecular structure may even be somewhat different from that of the terpenes.
Molecular Theory of Magnetism.
One of the fragments may again be broken, and again two bipolar magnets will be produced; and the operation may be repeated, at least in imagination, till we arrive at molecular magnitudes and can go no farther.
This experiment proves that the condition of magnetization is not confined to those parts where polar phenomena are exhibited, but exists throughout the whole body of the magnet; it also suggests the idea of molecular magnetism, upon which the accepted theory of magnetization is based.
The process of magnetization consists in turning round the molecules by the application of magnetic force, so that their north poles may all point more or less approximately in the direction of the force; thus the body as a whole becomes a magnet which is merely the resultant of an immense number of molecular magnets.
These observations have an important bearing upon the molecular theory of magnetism, which will be referred to later.
Weber's theory of molecular magnetism.
The width of the gap may be diminished until it is no greater than the distance between two neighbouring molecules, when it will cease to be distinguishable, but, assuming the molecular theory of magnetism to be true, the above statement will still hold good for the intermolecular gap. The same pressure P will be exerted across any imaginary section of a magnetized rod, the stress being sustained by the intermolecular springs, whatever their physical nature may be, to which the elasticity of the metal is due.
This explanation was not accepted by Wiedemann,' who thought that the effect was accounted for by molecular friction.
Until the mysteries of molecular constitution have been more fully explored, perhaps D may be most properly regarded as the fundamental phenomenon from which the others follow.
Among other researches relating to atomic and molecular magnetism are those of 0.
Molecular Theory Of Magnetism According to W.
Soc., 1890, 48, 342) has demonstrated that it is quite unnecessary to assume either the directive force of Weber, the permanent set of Maxwell, or any kind of frictional resistance, the forces by which the molecular magnets are constrained being simply those due to their own mutual attractions and repulsions.
With small magnetizing forces the hysteresis was indeed somewhat larger than that obtained in an alternating field, probably on account of the molecular changes being forced to take place in one direction only; but at an induction of about 16,00o units in soft iron and 15,000 in hard steel the hysteresis reached a maximum and afterwards rapidly diminished.
In one case the hysteresis loss per cubic centimetre per cycle was 16,100 ergs for B =1 5,900, and only 1200 ergs for B = 20,200, the highest induction obtained in the experiment; possibly it would have vanished before B had reached 21,000.2 These experiments prove that actual friction must be almost entirely absent, and, as Baily remarks, the agreement of the results with the previously suggested deduction affords a strong verification of Ewing's form of the molecular theory.
The fact being established that magnetism is essentially a molecular phenomenon, the next step is to inquire what is the constitution of a magnetic molecule, and why it is that some molecules are ferromagnetic, others paramagnetic, and others again diamagnetic. The best known of the explanations that have been proposed depend upon the magnetic action of an electric current.
Since that date it has more than once been suggested that the molecular currents producing magnetism might be due to the revolution of one or more of the charged atoms or " ions " constituting the molecule.
Diamagnetism, in short, is an atomic phenomenon; paramagnetism and ferromagnetism are molecular phenomena.
Weber's molecular theory, which has already been referred to, appeared in 1852.5 An event of the first importance was the discovery made in 1819 by H.
Ampere's experimental and theoretical investigation of the mutual action of electric currents, and of the equivalence of a closed circuit to a polar magnet, the latter suggesting his celebrated hypothesis that molecular currents were the cause of magnetism.
2 His well-known modification 3 of Weber's molecular theory, published in 1890, presented for the first time a simple and sufficient explanation of hysteresis and many other complexities of magnetic quality.
In the German Patent 1 57573 (1904) it is shown that by the action of at least two molecular proportions of an alkyl formate on two molecular proportions of a magnesium alkyl or aryl haloid, a complex addition compound is formed, which readily decomposes into a basic magnesium salt and an aldehyde, C H MgBr-f-H000R-ROï¿½CHï¿½C H.
Molecular physics also attracted his notice, and he announced in 1824 his purpose of treating the subject in a separate work.
But the increase of size which constitutes growth is the result of a process of molecular intussusception, and therefore differs altogether from the process of growth by accretion, which may be observed in crystals and is effected purely by the external addition of new matter - so that, in the well-known aphorism of Linnaeus, the word "grow" as applied to stones signifies a totally different process from what is called "growth" in plants and animals.
This, however, is not exactly accurate, if it be thereby implied that all living things have a visible organization, as there are numerous forms of living matter of which it cannot properly be said that they possess either a definite structure or permanently specialized organs: though, doubtless, the simplest particle of living matter must possess a highly complex molecular structure, which is far beyond the reach of vision.
A mass of living protoplasm is simply a molecular machine of great complexity, the total results of the working of which, or its vital phenomena, depend - on the one hand, Life con- of this water is absolutely incompatible with either moister by a ctual or potential life.
No method has yet been devised by which the molecular weight can be ascertained.'
conceptions will be opened out, not in bacteriology only, but also in biological chemistry and in molecular physics.
Now, what is remarkable in these and many other reactions is not only that effects apparently very opposite may result from minute differences of molecular construction, but also that, whatever the construction, agents, not wholly indifferent to the body or part, tend to anchor themselves to organic molecules in some way akin to them.
Putting (12) a vortex line is defined to be such that the tangent is in the direction of w, the resultant of, n, called the components of molecular rotation.
Projected perpendicularly against a plane boundary, the motion is determined by an equal opposite vortex ring, the optical image; the vortex ring spreads out and moves more slowly as it approaches the wall; at the same time the molecular rotation, inversely as the cross-section of the vortex, is seen to increase.
The plane projection of molecular structures which differ stereochemically is discussed under Stereoisomerism; in this place it suffices to say that, since the terminal groups of the hexaldose molecule are different and four asymmetric carbon atoms are present, sixteen hexaldoses are possible; and for the hexahydric alcohols which they yield on reduction, and the tetrahydric dicarboxylic acids which they give on oxidation, only ten forms are possible.
In regard to methods and apparatus, mention should be made of his improvements in the technique of organic analysis, his plan for determining the natural alkaloids and for ascertaining the molecular weights of organic bases b y means of their chloroplatinates, his process for determining the quantity of urea in a solution - the first step towards the introduction of precise chemical methods into practical medicine - and his invention of the simple form of condenser known in every laboratory.
The present article, as explained under Electrochemistry, treats only of those processes in which electricity is applied to the production of chemical reactions or molecular changes at furnace temperatures.
the production of graphite from coke or gas-carbon) the heat is applied solely to the production of molecular or physical changes.
Titanium trichloride, TiC131 forms involatile, dark violet scales, and is obtained by passing the vapour of the tetrachloride mixed with hydrogen through a red-hot tube, or by heating the tetrachloride with molecular silver to 200°.
The tertiary amines possess the power of combining with one molecular proportion of an alkyl iodide to form quaternary ammonium salts.
The composition of the distillate is determinate (by Avogadro's law) if the molecular weights and vapour pressure of the components at the temperature of distillation be known.
If M 1, M2, and P 1, P 2 be the molecular weights and vapour pressures of the components A and B, then the ratio of A to B in the distillate is M 1 P 1 /M 2 P 2.
P 1 greater than P2, if the molecular weight of A be much less than that of B, then it is obvious that the ratio M 1 P 1 /M 2 P 2 need not be very great, and hence the less volatile liquid B would come over in fair amount.
These con-, ditions pertain in cases where distillation with steam is successfully practised, the relatively high volatility of water being counterbalanced by the relatively high molecular weight of the other component; for example, in the case of nitrobenzene and water the ratio is I to 5.
He wrote a lucid account of the phenomena of phosphorescence, and adduced a molecular magnetic theory which anticipated some of the chief features of the hypothesis of to-day.
The isomerism which occurs as soon as the molecule contains a few carbon atoms renders any classification based on empirical molecular formulae somewhat ineffective; on the other hand, a scheme based on molecular structure would involve more detail than it is here possible to give.
When a quantity of heat, H, is supplied to a body, part is expended in raising the temperature of the body, or in expanding the volume against molecular forces, and is represented by an increase in the total quantity of energy contained in the body, which is generally called its Intrinsic Energy, and will be denoted by the symbol E.
The energy is less than that of an ideal gas by the term npc. If we imagine that the defect of volume c is due to the formation of molecular aggregates consisting of two or more single molecules, and if the kinetic energy of translation of any one of these aggregates is equal to that of one of the single molecules, it is clear that some energy must be lost in co-aggregating, but that the proportion lost will be different for different types of molecules and also for different types of co-aggregation.
If the molecules and molecular aggregates were more complicated, and the number of degrees of freedom of the aggregates were limited to 6, or were the same as for single molecules, we should have n-= so/R.
M, Molecular weight.
The problem of the stresses in rarefied gaseous media arising from inequalities of temperature, which is thereby opened out, involves some of the most delicate considerations in molecular physics.
In later memoirs Reynolds followed up this subject by proceeding to establish definitions of the velocity and the momentum and the energy at an element of volume of the molecular medium, with the precision necessary in order that the dynamical equations of the medium in bulk, based in the usual manner on these quantities alone, without directly considering thermal stresses, shall be strictly valid - a discussion in which the relation of ordinary molar mechanics to the more complete molecular theory is involved.
Hull, with the result that there is a certain pressure at which the molecular effect of the gas.
The density gives very important information as to the molecular weight, since by the law of Avogadro it is seen that the relative density is the ratio of the molecular weights of the experimental and standard gases.
This subject owes its importance in modern chemistry to the fact that the vapour density, when hydrogen is taken as the standard, gives perfectly definite information as to the molecular condition of the compound, since twice the vapour density equals the molecular weight of the compound.
Biltz, Practical Methods for determining Molecular Weights (1899).
For the detailed chemical significance of these terms, see Chemistry; and for the atomic theory of the chemist (as distinguished from the atomic or molecular theory of the physicist) see Atom; reference may also be made to the article Matter.
The leading historical stages in the evolution of the modern conception of the molecular structure of matter are treated in the following passage from James Clerk Maxwell's article Atom in the 9th edition of the Ency.
" The opposite school maintained then, as they have always done, 1 It wiII be noted that Clerk Maxwell's " atom " and " atomic theory " have the significance which we now attach to " molecule " and " molecular theory."
In this way the science of hydrostatics may be built upon an experimental basis, without any consideration of the constitution of a fluid as to whether it is molecular or continuous.
THE Molecular Structure Of Matter An enormous mass of experimental evidence now shows quite conclusively that matter cannot be regarded as having a continuous structure, but that it is ultimately composed of discrete parts.
In point of fact it is found that the properties which are most easily explained are those connected with the gaseous state; the explanation of these properties in terms of the molecular structure of matter is the aim of the " Kinetic Theory of Gases."
The results of this theory have placed the molecular conception of matter in an indisputable position, but even without this theory there is such an accumulation of electrical and optical evidence in favour of the molecular conception of matter that the tenability of this conception could not be regarded as open to question.
Apart from speculation, the first definite evidence for the molecular structure of matter occurs when it is found that certain physical phenomena change their whole nature as soon as we deal with matter of which the linear dimensions are less than a certain amount.
The agreement of the values obtained for the same quantity by different methods provides valuable confirmation of the truth of the molecular theory and of the validity of the methods of the kinetic theory of gases.
Roughly speaking, it is found that there are three main types of molecular motion corresponding to the three states of matter - solid, liquid and gaseous.
As a preliminary to examining further into the nature of molecular motion and the differences of character of this motion, let us try to picture the state of things which would exist in a mass of solid matter in which all the molecules are imagined to be at rest relatively to one another.
Thus the molecular theory of matter, as we have now pictured it, leads us to identify heat-energy in a body with the energy of motion of the molecules of the body relatively to one another.
The point of view which has now been gained enables us to interpret most of the thermal properties of solids in terms of molecular theory.
This is the conception which the molecular theory compels us to form of the gaseous state.
In terms of the molecular theory this indicates that the total energy of the gas is the sum of the separate energies of its different molecules: the potential energy arising from intermolecular forces between pairs of molecules may be treated as negligible when the matter is in the gaseous state.
The kinetic theory of gases attempts to give a mathematical account, in terms of the molecular structure of matter, of all the non-chemical and non-electrical properties of gases.
The determination of the series of configurations developing out of given initial conditions is not, however, the problem of the kinetic theory: the object of this theory is to explain the general properties of all gases in terms only of their molecular structure.
If in formula Molecular (?3) we put p=I 013X10 6, (v +v'+ ..
If p is the density corresponding to pressure p, we find that,}, formula (Ii) assumes the form P = 3PC2, where C is a velocity such that the gas would have its actual translational energy if each molecule moved with the same velocity C. By substituting experimentally determined pairs of values of p and p we can calculate C for different gases, and so obtain a knowledge of the magnitudes of the molecular velocities.
von Nageli's investigations on molecular structure and the growth of the cell membrane we recognize the origin of modern methods of the study of cellstructure included under cytology.
Soc., 1889, 55, p. 163) determined the vapour density of hydrofluoric acid at different temperatures, and showed that there is no approach to a definite value below about 88° C. where it reaches the value 10.29 corresponding to the molecular formula HF; at temperatures below 88° C. the value increases rapidly, showing that the molecule is more complex in its structure.
But in the transition from molecular theory to the electrodynamics of extended media, all magnetism has to be replaced by a distribution of current; the latter being now specified by volume as well as by flow so that (u,v,w) ST is the current in the element of volume 6T.
Lorentz, on the general lines suggested by the electron-theory of molecular constitution.
This fact, coupled with the determination of the vapour density of the gas, establishes the molecular formula CO.
This was based on the assumption that the medium in which the light is propagated is discontinuous and molecular in character, the molecules being subject to a mutual attraction.
Silver cyanide, AgNC, is formed as a white precipitate by adding potassium cyanide to silver nitrate solution; or better, by adding silver nitrate to potassium silver cyanide, KAg(NC) 2, this double cyanide being obtained by the addition of one molecular proportion of potassium cyanide to one molecular proportion of silver nitrate, the white precipitate so formed being then dissolved by adding a second equivalent of potassium cyanide.
In many of these salts one finds that the elements of water are frequently found in combination with the metal, and further, that the ammonia molecule may be replaced by such other molecular groups as - N02, &c. Of the types studied the following may be mentioned: the diammine chromium thiocyanates, M[Cr(NH3)2 (SCN)4], the chloraquotetrammine chromic salts, R 1 2 [Cr(NH 3) 4 H 2 0 C1], the aquopentammine or roseo-chromium salts,R 1 3 [Cr(NH 3) 6.
They may also be obtained by the molecular rearrangement of the diazoamines, when these are warmed with the parent base and its hydrochloride.
Spectrum analysis thus passed quickly out of the stage in which its main purpose was " analysis " and became our most delicate and powerful method of investigating molecular properties; the old name being no longer appropriate, we now speak of the science of " Spectroscopy."
When the molecule is losing energy the intensity of each kind of radiation depends principally on the rapidity with which it can be renewed by molecular impacts.
Radiation is a molecular process, and we can speak of the radiation of a molecule but not of its temperature.
highest temperatures at our command it is small compared with the energy of translatory motion, but as the temperature increases, it must ultimately gain the upper hand, and if there is anywhere such a temperature as that of several million degrees, the greater part of the total energy of a body will be outside the atom and molecular motion ultimately becomes negligible compared with it.
The homogeneity of vibration may also be diminished by molecular impacts, but the number of shocks in a given time depends on pressure and we may therefore expect to diminish the width of a line by diminishing the pressure.
It is not, however, obvious that the sudden change of direction in the translatory motion, which is commonly called a molecular shock, necessarily also affects the phase of vibration.
Such spectra seem to be characteristic of complex molecular structure, as they appear when compounds are raised to incandescence without decomposition, or when we examine the absorption spectra of vapours such as iodine and bromine and other cases where we know that the molecule consists of more than one atom.
If the medium which contains the vibration is divided into a sphere equal to k times the molecular vibration outside of which the effects of these molecules may be averaged up, so that its Roy.
The subject wants further investigation, especially with a view to deciding the connexion between the molecular rush and the discharge.
While some of the phenomena seem to indicate that the projection of metallic vapours into the centre of the spark is a process of molecular diffusion independent of the mechanism of the discharge, the different velocities obtained with bismuth, and the probability that the vibrating systems are not electrically neutral, seem to indicate that the projected metallic particles are electrified and play some part in the discharge.
When we now speak of the identification of spectra we like to include, wherever possible, the identification of the particular compound which is luminous and even - though we have only begun to make any progress in that direction - the differentiation between the molecular or electronic states which yield the different spectra of the same element.
To explain this great variability of spectroscopic effects we may either adopt the view that molecular aggregates of semi-stable nature may be found in vacuum tubes, or that a molecule may gain or lose one or more additional electrons and thus form new vibrating systems. It seemed that an important guide to clear our notions in this direction could be obtained through the discovery of J.
It will be remembered that Fechner regarded every composite body as the appearance of a spirit; so that when, for example, molecular motion of air is said to cause a sensation of sound in me, it is really a spirit appearing as air which causes the sensation in my spirit.
He ingeniously suggested that the external agent is one feeling regarded objectively, and the internal effect another feeling regarded subjectively; " and therefore," to quote his own words, " to say that it is a molecular movement which produces a sensation of sound, is equivalent to saying that a sensation of sight produces a sensation of hearing."
That orthoboric acid is a tribasic acid is shown by the formation of ethyl orthoborate on esterification, the vapour density of which corresponds to the molecular formula B(0C2H5)3; the molecular formula of the acid must consequently be B(OH) 3 or H 3 B0 3.
The original memoirs themselves on radiant heat and on magnetism were collected and issued as two large volumes under the following titles: Diamagnetism and Magne-crystallic Action (1870); Contributions to Molecular Physics in the Domain of Radiant Heat (1872).
The process of cooling is thus represented by a path which runs vertically downwards till it cuts the 0 Molecular Percentage of Na t S04 Siluer Copper FIG.
On the fundamental hypotheses of the molecular theory, Value we must regard a solution as composed of a number osmotic of separate particles of solute, scattered through- p out the solvent.
A quantity of gas measured by its molecular weight in grammes when confined in a volume of one litre exerts a pressure of 22.2 atmospheres, and thus the osmotic pressure of a dilute solution divided by its concentration in gramme-molecules per litre has a corresponding value.
In the vapour pressure equation p - p' = Pa/p, we have the vapour density equal to M/v 1, where M is the molecular weight of the solvent.
Each molecular complex, formed by solution and solvent, is treated as a single molecule.
The solution of sodium aluminate, containing aluminium oxide and sodium oxide in the molecular proportion of 6 to 1, is next agitated for thirty-six hours with a small quantity of hydrated alumina previously obtained, which causes the liquor to decompose, and some 70% of the aluminium hydroxide to be thrown down.
But carbon affects the properties of iron not only by giving rise to varying proportions of cementite, but also both by itself shifting from one molecular state to another, and by enabling us to hold the iron itself in its unmagnetic allotropic forms, 0and 7-iron, as will be explained below.
In the cold this transformation cannot take place, because of molecular rigidity or some A C VII' B Solid ' Legend' ustenite diagram = Comentite-Austenite diagram show) for comparison ...
Primary a Austenite 'Molten Metal ' usually to between 200° and 300° C., so as to relax the molecular rigidity and thereby to allow the arrested transformation to go on a little farther, shifting a little of the 0-iron over into the a state.
that to which the hardened steel is thus reheated, the more is the molecular rigidity relaxed, the farther on does the transformation go, and the softer does the steel become; so that, if the reheating reaches a dullred heat, the transformation from austenite into ferrite and cementite completes itself slowly, and when now cooled the steel is as soft and ductile as if it had never been hardened.
The molecular freedom which this high temperature gives enables the cementite to change gradually into a mixture of graphite and austenite with the result that, after the castings have been cooled and their austenite has in cooling past Aci changed into pearlite and ferrite, the mixture of cementite and pearlite of which they originally consisted has now given place to one of fine or " temper " graphite and ferrite, with more or less pearlite according to the completeness of the transfer of the carbon to the state of graphite.
In carrying out this process the castings are packed in a mass of iron oxide, which at this temperature gradually removes the fine or " temper " graphite by oxidizing that in the outer crust to carbonic oxide, whereon the carbon farther in begins diffusing outwards by " molecular migration," to be itself oxidized on reaching the crust.
Jochem (Ber., 1901, 34, p. 3337), who arrived at the conclusion that the normal decomposition of diazonium salts by alcohols results in the formation of phenolic ethers, but that an increase in the molecular weight of the alcohol, or the accumulation of negative groups in the aromatic nucleus, diminishes the yield of the ether and increases the amount of the hydrocarbon formed.
On mixing dilute solutions of the diazonium hydroxide and the alkali together, it is found that the molecular conductivity of the mixture is much less than the sum of the two electrical conductivities of the solutions separately, from which it follows that a portion of the ions present have changed to the non-ionized condition.
Cryoscopic determinations of its molecular weight show that it is H 2 0 2.
The one group included those isomers where the identity in composition was accompanied by identity in molecular weight, i.e.
the vapour densities of the isomers were the same, as in butylene and isobutylene, to take the most simple case; here the molecular conception admits that the isolated groups in which the atoms are united, i.e.
iroXb, many) was chosen for compounds like butylene, C 4 H 8, and ethylene, C 2 H 4, corresponding to the same composition in weight but differing in molecular formula, and having different densities in gas or vapour, a litre of butylene and isobutylene weighing, for instance, under ordinary temperature and pressure, about 2.5 gr., ethylene only one-half as much, since density is proportional to molecular weight.
Polymerism required no particular explanation, since this was given by the difference in molecular magnitude.
The cases of mutual transformation are generally characterized by the fact that in the compound of higher molecular weight no new links of carbon with carbon are introduced, the trioxymethylene being O CH2-0 CH 2 whereas honey-sugar correg probably C C H 2 -0% sponds to CH 2 0H [[Choh Choh Choh Choh Cho]], each point representing a linking of the carbon atom to the next.
The conception of metamerism, or isomerism in restricted sense, has been of the highest value for the development of our notions concerning molecular structure, i.e.
By Wilhelm Ostwald especially, attempts have been made to substitute the notion of atoms and molecular structure by less hypothetical conceptions; these ideas may some day receive thorough confirmation, and when this occurs science will receive a striking impetus.
The third most valuable indication which molecular structure gives about these isomers is how to prepare them, for instance, that normal hexane, represented by CH 3 CH 2 CH 2 CH 2 CH 2 CH3, may be obtained by action of sodium on propyl iodide, CH 3 CH 2 CH 2 I, the atoms of iodine being removed from two molecules of propyl iodide, with the resulting fusion.
In this equation a relates to molecular attraction; and it is not improbable that in isomeric molecules, containing in sum the same amount of the same atoms, those mutual attractions are approximately the same, whereas the chief difference lies in the value of b, that is, the volume occupied by the molecule itself.
Now taking the isomers H 3 C CC1 3 (M„ = 108) and C1H 2 C CHC1 2 (M„ = we see the negative chlorine atoms heaped up in the left hand formula, but distributed in the second; the former therefore may be presumed to occupy a larger space, the molecular volume, that is, the volume in cubic centimetres occupied by the molecular weight in grams, actually being 108 in the former, and 103 in the latter case (compare Chemistry: Physical).
Conduction, however, is generally understood to include diffusion of heat in fluids due to the agitation of the ultimate molecules, which is really molecular convection.
Its vapour density has been determined by Nilson and Pettersson, and corresponds to the molecular formula BeC12.
According to Rabuteau the toxic properties of the higher alcohols increase with their molecular weight and boiling point.
Perceiving a molecular isonomy between them and the inorganic compounds of the metals from which they may be formed, he saw their true molecular type in the oxygen, sulphur or chlorine compounds of those metals, from which he held them to be derived by the substitution of an organic group for the oxygen, sulphur, &c. In this way they enabled him to overthrow the theory of conjugate compounds, and they further led him in 1852 to publish the conception that the atoms of each elementary substance have a definite saturation capacity, so that they can only combine with a certain limited number of the atoms of other elements.
The Well Known Experiments Of Regnault And Wiedemann On The Specific Heat Of Gases At Constant Pressure Agree In Showing That The Molecular Specific Heat, Or The Thermal Capacity Of The Molecular Weight In Grammes, Is Approximately Independent Of The Temperature And Pressure In Case Of The More Stable Diatomic Gases, Such As 112,02, N2, Co, &C., And Has Nearly The Same Value For Each Gas.
Since Much Smaller Values Are Found For More Complex Molecules, We May Suppose That, In These Cases, The Energy Of Rotation Of A Polyatomic Molecule May Be Greater Than Its Energy Of Translation, Or Else That Heat Is Expended In Splitting Up Molecular Aggregates, And Increasing Energy Of Vibration.
Atomic And Molecular Heats.
For A Diatomic Gas, The Molecular Heat Would Be Nearly Five Calories, Or The Atomic Heat Of A Gas In The Diatomic State Would Be 2.5.
No Doubt There Must Be Approximate Relations Between The Atomic And Molecular Heats Of Similar Elements And Compounds, But Considering The Great Variations Of Specific Heat With Temperature And Physical State, In Alloys, Mixtures Or Solutions, And In Allotropic Or Other Modifications, It Would Be Idle To Expect That The Specific Heat Of A Compound Could Be Accurately Deduced By Any Simple Additive Process From That Of Its Constituents.
For example, from the evidence of molar changes due to the obvious parts of bodies, science first comes to believe in molecular changes due to imperceptible particles, and then tries to conceive the ideas of particles, molecules, atoms, electrons.
(The human soul is still an exception.) Form is bound up with the molecular structure and change of structure of a body, one of whose qualities or activities it expresses in wider relations.
(8) where is the molecular weight of the vapour, and R the gasconstant which is nearly 2 calories per degree for a gramme-molecule of gas.
The most important apparent exceptions to Raoult's law in dilute solutions are the cases, (I) in which the molecules of the dissolved substance in solution are associated to form compound molecules, or dissociated to form other combinations with the solvent, in such a way that the actual number of molecules n in the solution differs from that calculated from the molecular weight corresponding to the accepted formula of the dissolved substance; (2) the case in which the molecules of the vapour of the solvent are associated in pairs or otherwise so that the molecular weight m of the vapour is not that corresponding to its accepted formula.
p. 631) showed how to calculate the effective number of molecules n" = (1 +ek/ko)n,from the molecular conductivity k of the solution and its value ko at infinite dilution, for an electrolyte giving rise to e +I ions.
The theory of the ionization of salts in solution has raised much discussion amongst chemists, but the general fact is certain that electricity only moves through liquids in association with matter, and simultaneously involves chemical dissociation of molecular groups.
The next step is to deduce this surface-tension from a hypothesis as to the molecular constitution of the liquid and of the bodies that surround it.
The scientific importance of this step is to be measured by the degree of insight which it affords or promises into the molecular constitution of real bodies by the suggestion of experiments by which we may discriminate between rival molecular theories.
But for those who wish to study the molecular constitution of bodies it is necessary to study the effect of forces which are sensible only at insensible distances; and Laplace has furnished us with an example of the method of this study which has never been surpassed.
The only difference is in the manner in which this quantity H depends on the law of the molecular forces and the law of density near the surface of the fluid, and as these laws are unknown to us we cannot obtain any test to discriminate between the two theories.
The experimental evidence which Dupre obtained bearing on the molecular structure of liquids must be very valuable, even if our present opinions on this subject should turn out to be erroneous.
[The continued coexistence of various thicknesses, as evidenced by the colours in the same film, affords an instantaneous proof of this conclusion.] The phenomena of very thin liquid films deserve the most careful study, for it is in this way that we are most likely to obtain evidence by which we may test the theories of the molecular structure of liquids.
If, however, it were negative, the displacement of the liquids which tends to enlarge the surface of contact would be aided by the molecular forces, so that the liquids, if not kept separate by gravity, would at length become thoroughly mixed.
In such a film it is possible that no part of the liquid may be so far from the surface as to have the potential and density corresponding to what we have called the interior of a liquid mass, and measurements of the tension of the film when drawn out to different degrees of thinness may possibly lead to an estimate of range of the molecular forces, or at least of the depth within a liquid mass, at which its properties become sensibly uniform.
We shall therefore endeavour to apply to this subject the methods used in Thermodynamics, and where these fail us we shall have recourse to the hypotheses of molecular physics.
Integrating with respect to f from f =z to f=a, where a is a line very great compared with the extreme range of the molecular force, but very small compared with either of the radii of curvature, we obtain for the work (1,G (z) - 111(a))dw, and since (a) is an insensible quantity we may omit it.
Hence the tension is the same for all films thicker than e, the range of the molecular forces.
In fact, the quantity 41rp 2 K, which we may call with van der Waals the molecular pressure, is so great for most liquids (5000 atmospheres for water), that in the parts near the surface, where the molecular pressure varies rapidly, we may expect considerable variation of density, even when we take into account the smallness of the compressibility of liquids.
Suppose that the transition from o to s is made in two equal steps, the thickness of the intermediate layer of density la being large compared to the range of the molecular forces, but small in comparison with the radius of curvature.
All such phenomena, however, are likewise due to the disturbance of the molecular constitution of living cells.
Still another view, advocated by Bordet, is that the union of toxin and antitoxin is rather of physical than of strictly chemical nature, and represents an interaction of colloidal substances, a sort of molecular deposition by which the smaller toxin molecule becomes entangled in the larger molecule of antitoxin.
In 1844, by experiments on the tenacity of soap-bubbles, he showed that the molecular cohesion of water is equal (if not superior) to that of ice, and hence, generally, that solids and their liquids have practically the same amount of cohesion (Proc. Am.
Molecular silver is a grey powder obtained by leaving metallic zinc in contact with silver chloride which has been precipitated in the cold and washed till nearly free from acid.
Hydrobromic acid is one of the "strong" acids, being ionized to a very large extent even in concentrated solution, as shown by the molecular conductivity increasing by only a small amount over a wide range offdilution.
For the molecular theory of absorption, see SPECTROSCOPY.
It exists in two forms, one having the formula P 4 5 10, and the other a lower molecular weight.
The term "perfect gas" is applied to an imaginary substance in which there is no frictional retardation of molecular motion; or, in other words, the time during which any molecule is influenced by other molecules is infinitesimally small compared with the time during which it traverses its mean free path.
It also dissolves in alcohol and ether; boiling point determinations of the molecular weight in these solutions point to the formula FeCl3.
Her other works are the Connexion of the Physical Sciences (1834), Physical Geography (1848), and Molecular and Microscopic Science (1869).
Divers obtains it by mixing cold saturated solutions containing one molecular proportion of sodium nitrate, and two molecular proportions of acid sodium sulphite, and then adding a saturated solution of potassium chloride to the mixture.
It has been maintained, on the one hand, that any theory which presupposes a direct correspondence between the molecular movements of the brain, and the states of consciousness which accompany them must make the freedom of the will impossible.
No direct causal relationship between a molecular movement and a state of consciousness has ever been established.
And many scientific thinkers, while professing allegiance to a theory which insists upon the independence of each parallel series, in reality tacitly assume the superior importance if not the controlling force of the physical over the psychical terms. But a mere insistence upon the complete independence of the physical series coupled with the belief that its changes are wholly explicable as modes of motion, that the study of molecular physics is competent to explain all the phenomena of life and organic movements, is sufficient to eliminate the possibility of spontaneity and free origination from the universe.
The physical properties of the alcohols exhibit a gradation with the increase of molecular weight.
A modification in this proposition which may hereafter be accepted involves an extension of our ideas of temperature, and leads us to regard the interior heat of the heavenly bodies as due to a form of molecular activity similar to that of which radium affords so remarkable an instance.
If unit mass of a solution contain m grammes of an active substance and if o be the density and p be the rotary power of the solution, the specific rotary power is defined by p/m8, and the molecular rotary power is obtained from this by multiplying by the hundredth part of the molecular mass.
He studied with attention the still obscure subject of molecular cohesion, and little has been added to what he ascertained on the question of transverse strains and the strength of beams, first brought by him within the scope of mechanical theory.
Phthalimide, C6H4(CO)2NH, is formed by heating phthalic anhydride or chloride in ammonia gas or by molecular rearrangement of ortho-cyanbenzoic acid.
But under the influence of Thomas Thomson (1773-1852), the professor of chemistry, he developed a taste for experimental science and especially for molecular physics, a subject which formed his main preoccupation throughout his life.
Friction is preferably spoken of as "resistance" rather than "force," for a reason exactly the same as that which induces us to treat stress rather as molecular resistance (to change of form) than as force, and which may be stated thus: although friction can be utilized as a moving force at will, and is continually so used, yet it cannot be a primary moving force; it can transmit or modify motion already existing, but cannot in the first instance cause it.
In addition to these normal salts, others exist, namely bichromates, trichromates, &c., which may be regarded as combinations of one molecular proportion of the normal salt with one or more molecular proportions of chromium trioxide.
There was a predilection for certain sites, the molecular basis of which remains obscure.
This process is defined as molecular adsorption on the surfaces of solids.
For simple organic molecules, including alkanes, alkenes and cycloalkanes, construct appropriate isomeric forms, given a molecular formula 11.
alkanes increase with molecular size.
Examples silica gel, activated alumina, molecular sieve.
Do not use full-dose low molecular weight heparin or other new anticoagulants without seeking advice first.
Molecular characters have been used in conjunction with morphological characters to understand patterns of evolution within the genus arum.
Such cancelation would significantly reduce the liquidity and marketability of any Molecular Sensing Shares not assented to the Offer.
Her research project is focused on the molecular basis of inherited ataxia in people living in the North East of England.
The III incorporates multiple research groups with expertise in molecular bacteriology, virology, chemical biology, immunology and cancer immunity.
In the following two years a very wide range of subjects is covered relating to molecular and cellular biochemistry.
The Department spans all areas from molecular and cellular through to biophysics and computational biochemistry.
Research areas include bioenergetics, molecular biology, fermentation, protein biochemistry, kinetic and paramagnetic spectroscopy and X-ray crystallography.
molecular biogeography uses information about the rate of changes in DNA sequences to estimate when evolutionary events occurred.
The molecular biology of the Cell 4 th edition Garland Science 2002.
A group of free tools for computational molecular biology with Python.
Current research is focused mainly on molecular plant science and molecular biomedicine.
Looking to the future growth areas that may have a big impact are nanotechnology, quantum computing and molecular biophysics.
Applicants should have a strong record of productivity and a background of research excellence in molecular biology, cell biology or cellular biophysics.
AIMS The course will provide a basic grounding in key aspects of molecular bioscience with an emphasis on bioscience engineering.
The group collaborates with DSTL at Porton Down in developing molecular biosensors.
molecular biotechnology, 22, (2 ), 179-189.
Molecular genetic analysis of tumor cell DNA was done by southern blot.
browser plug-in based on the popular molecular viewer software, RasMol.
This experimental program will be supported by state-of-the-art molecular orbital calculations.
calm public fears by simply denying the feasibility of molecular manufacturing will inevitably fail.
We are currently elucidating the molecular mechanisms responsible for the adjuvant and immune biasing activity of reactive carbonyls and methods for their elimination.
cascade lasers and semiconductor growth by molecular beam epitaxy.
This leads to the production of radical molecular cations and anions of large biomolecules.
molecular characterization of the Rep protein of the black gram isolate of Indian mungbean yellow mosaic virus.
chlorella virus particles are large (molecular weight ~1 x 10 9 Da) and complex.
The gel permeation chromatography (GPC) measurements show that the molecular weight profile is only changed slightly.
Research in the Group is focussed on molecular and human chronobiology investigating the causes, consequences and treatment of circadian rhythm disorders.
However little is known of the molecular mechanisms and neuronal circuitry underlying gravitational responses.
molecular cloning: Laboratory Manual 2nd edn New York, Cold Spring Harbor Laboratory chapter 10, pp 59-61.
We plan to make a " molecular tool box " for the genetic manipulation of the genus clostridium.
molecular shape complementarity is important because bumps and clashes lead to repulsion, while failing adequately to bury hydrophobic surfaces has an entropic cost.
Programs for analyzing molecular shape and measuring shape complementarity for docked complexes are available for download, including FADE and PADRE.
It consists of high molecular weight hydrocarbons and minor amounts of sulfur and nitrogen compounds.
The two molecules are virtually identical in their molecular conformation.
This proposal aims both to simplify our existing molecular identification system for Calanus spp., and to expand it to include other common copepods.
We have used molecular modeling methods to study the interfaces between calcite crystals and monolayers of stearic acid.
Identification and molecular characterization of viruses infecting cucurbits in Pakistan.
The molecular structure of an unusual cytochrome c 2 determined at 2.0?
This page profiles the job areas of research, clinical cytogenetics, molecular cytogenetics, and counseling.
human cytogenetics Diagnostic molecular genetics Population, screening and biochemical genetics Clinical aspects of medical genetics Problem sessions Term 3: Group work.
In this way, we will build up a pathway of molecular events and their regulation during the early stages of axon degeneration.
We attempted to characterize these chromosome 13q deletions at the molecular cytogenetic level.
We have also studied S. pupula demes using molecular sequence data, from 18S rDNA, ITS and rbc L sequences.
Up to now, evolutionary developmental biology, in its search for conserved molecular factors, has mainly focussed on this compositional aspect.
She was treated with high dose oral steroids, low molecular weight dextran and vasodilators with benefit.
Dr. Malcolm Law - 7 June 2006 Evaluation of molecular tests for prenatal diagnosis of chromosome abnormalities.
Techniques using the dipolar field can provide more than just a measure of molecular self diffusion.
We are using FT-ICR MS (and specifically electron capture dissociation) along with molecular modeling to probe their gas phase structures.
By measuring genetic divergence between populations using molecular markers, I hope to relate this host specificity to the process of incipient speciation.
dogma of molecular biology.
This R factor corresponds to the relative motions occurred during molecular dynamics (see more at flexibility ).
Research Interests: The use of molecular genetic methods to resolve questions in plankton ecology using CPR samples.
It combines the perspectives of molecular genetics, evolutionary biology and pollination ecology.
HP have used memory bits made of rotaxanes, rather than silicon - the first significant demonstration of ' molecular electronics ' .
elucidatecurrently elucidating the molecular mechanisms responsible for the adjuvant and immune biasing activity of reactive carbonyls and methods for their elimination.
We use a range of genetic and embryological techniques including transgenesis, descriptive molecular embryology and the analysis of cell lineage.
Research within the Department is performed in the area of molecular and cellular endocrinology, and details of the current research projects are available.
molecular endocrinology, Molecular Medicine Center, University of Edinburgh, UK.
Molecular strategy for ' serotyping ' of human enteroviruses.
On finishing my PhD I would like to continue research in the area of molecular enzymology.
An additional research interest is in the molecular epidemiology of tuberculosis.
We have a national facility within the condensed matter group for the production of thin magnetic films by molecular beam epitaxy.
The molecular weight of the native protein determined from sedimentation equilibrium in buffers containing from 50 to 200 mM KCl is 20,000.
In an attempt to identify the molecular etiology of the tumors DNA was extracted from paraffin fixed tissue from both patients.
Adaptive radiation and molecular evolution of Cicindela tiger beetles.
FTIR allows identification of a substance by comparing the molecular fingerprint of the sample to a library of known spectra.
Molecular evidence for genetic mixing of Arctic and Antarctic subpolar populations of planktonic foraminifers.
We are interested in the molecular mechanisms involved in patterning the early mammalian forebrain.
This data indicates a molecular formula of C 28 H 42.
My snail porridge dish - that's my cooking - not molecular gastronomy.
gel permeation chromatography (GPC) measurements show that the molecular weight profile is only changed slightly.
Main research interests are the molecular typing of bacteria and characterisation of antibiotic resistance genes.
Prospects web - profile of a clinical molecular geneticist from the official UK graduate careers website.
Main research interests are in the development and use of molecular genetic markers for the management of natural populations and farmed fish.
Practical instruction is provided in gene cloning, molecular genetics, PCR and RFLP and haplotype analysis.
Human molecular genetics Human molecular genetics, available in full text or abstract form.
Molecular genetic studies in motor neuron disease: search for interactors with the glial glutamate transporter, EAAT2.
glycoprotein with a molecular weight of 10,000.
Figure 5. molecular gyroscope made of the CB@CB complex One of the main problems encountered with CB is its poor solubility in water.
Solution method: A molecular Hamiltonian describing carbon dioxide, which is a linear triatomic, is diagonalized.
Safety of low molecular weight heparin in pregnancy: a systematic review.
herbivore attack both result in reduced growth and ongoing projects are examining the molecular basis of this response.
heterodyne instruments for molecular line detection.
Apart from the most trivial cases (for example, burning hydrocarbons ), never use a molecular formula.
molecular hydrogen (H2) is under discussion to become the energy carrier of the future.
Non-invasive molecular imaging of epithelial cancer It is estimated that more than 85% of all cancers originate in the epithelium.
Hot topics in molecular and cellular immunology: current research at the cutting edge in Aberdeen and beyond.
He is Professor of molecular immunology in the Department.
imprinted polymers and the rational design of polymers using molecular modeling and computational chemistry.
A new technique called molecular imprinting may provide an answer.
Spatially inhomogeneous optical excitation may provide a means of movement control of the molecular motors.
Alastair McCartney presented a paper on new technologies including molecular methods for detecting airborne inoculum.
The institute for Stem Cell Research is a multidisciplinary research institute focused on the molecular, cellular and developmental biology of stem cells.
The ultimate responsibility of the position is to drive sustainable digital molecular imaging instrumentation growth within the European continent.
Less is more Packing more devices onto the same-size chip is not the only advantage to building an integrated circuit with molecular junctions.
We begin by feeding in details of the molecular interactions.
Main research interest is in the molecular basis of complex traits.
intricacyge databanks of molecular structures, to the UK census or the intricacies of animal behavior, academics handle enormous amounts of data.
Atomic or molecular transitions are often induced by the screened Coulomb potentials of atoms or partially ionized ions.
For example, there are two structural isomers with the molecular formula C 3 H 7 Br.
isotropic scattering, accurate molecular weight measurements can be made at a single angle.
Future studies will also help to clarify the molecular mechanisms involved in the chaperone activity of raft lipids.
These questions could easily be answered by molecular genetic analysis of the virus or viruses from infected livestock in the outbreak.
A copy of the program can be downloaded as a PDF file and contains an introduction to molecular magnetism.
As a result of genome mapping and gene display technologies, new molecular markers are being identified with increasing accuracy and rapidity.
Samples were then run on an ABI 377 gene scan analysis gel with an internal molecular weight marker.
The estimated molecular mass of the protein was around 95 kDa.
On a molecular level they resemble massive braided steal cables.
The molecular mechanism behind the activation process remains obscure.
Outline content: The shoot meristem; molecular control of vegetative growth and phase change.
Molecular Ecology of Methane oxidation We have been developing molecular biology techniques to study the ecology of methane oxidation We have been developing molecular biology techniques to study the ecology of methane oxidizers.
molecular microbiology (2003 ), 47 in press.
microscopy primer from the Molecular Expressions site.
Tsetse Research Laboratory, Bristol University Molecular basis of tsetse immunity / molecular characterisation of the tsetse fly midgut lectin.
Another innovative step in the on-going battle to improve pearl millet has been in the area of molecular mapping.
These antibodies will be used in the study of molecular mimicry in the context of autoimmune uveitis.
Freeman is the only molecular biologist on the commission, coming from a background in Drosophila (fruitfly) research.
molecular biology turned into a whole new career.
molecular biologist from the too simple to the too complex.
molecular orbitals will be deemed active in the MP calculation.
molecular mechanism behind the activation process remains obscure.
molecular dynamics (see more at flexibility ).
It is also possible to predict polymer specificity using molecular modeling.
Cancer bioinformatics aims to integrate molecular, biological and clinical knowledge about cancer with analytic methods from bioinformatics.
During the calculation of structures considerations of theoretical chemistry and applied molecular modeling are also taken into account.
molecular biology of some DNA viruses.
molecular biology of cancer.
molecular biology of this disease translate into new ways for its early detection and treatment?
molecular biology of raw materials The sensory perception of product quality and the psychology of consumer choice.
This tool is provided by Computational molecular biology at the US National Institutes of Health.
molecular biology involved, nor chemistry or quantum physics with string theory.
Synthetically manufactured peptide antigens and antigens produced using molecular biology are also being examined in an attempt to improve test specificity.
structural molecular biology: Students who pass Principles of Protein Structure and then one of the other two courses become eligible for the M.Sc.
molecular biologyourse (genetics, molecular cell biology, ecology, 4-year sandwich courses) is outlined at a modular level.
Exercise You are provided with a spectrum of a compound (identified with a letter) having the molecular formula C 6 H 14.
Structural isomerism occurs when two or more organic compounds have the same molecular formulae, but different structures.
Synthesis of acidic aluminosilicate mesoporous molecular sieves using primary amines, Chem.
Molecular shape can be estimated, when the absolute molecular weight (MW) is known.
Polypropylene can be made auxetic by compacting ultra high molecular weight PP powder, with a particle size of 30 to 120 microns.
monoclonal antibody therapy and molecular targeted small molecule therapy are becoming a reality in the treatment of many diseases.
multidisciplinary research institute focused on the molecular, cellular and developmental biology of stem cells.
We are using molecular genetic approaches, in particular random mutagenesis, to analyze fungal genes involved in the disease process.
For this we are using molecular modeling to investigate docking of the novel compounds, as well as conventional mutagenesis and expression techniques.
Genetic and molecular analyzes of recently isolated mutants aim to unravel the molecular network involved in hepatic specification and organ bud formation.
It provides a brief introduction to the core concepts of molecular nanotechnology.
The presence of oncogenic high risk HPV DNA is, at present, the best molecular marker for assessing the risk of cervical neoplasia.
There is a joint program with cardiovascular medicine on the molecular genetics of myocardial contractile proteins, and on integrated cardiac neurobiology.
Cellular and Molecular neuropharmacology of 5-HT The cellular and molecular neuropharmacology research group is headed by Dr. Nick Barnes and Dr. Tony Hope.
Sharma completed a PhD in molecular neuroscience at The School of Pharmacy, University of London.
This sequence of events requires molecules that respond to electrical energy and then interact with other molecular mechanisms which release the chemical neurotransmitters.
We are collaborating on an exhaustive molecular characterisation of cancer cell lines to identify novel oncogenes and tumor suppressor genes in ovarian cancer.
Biochemical and molecular approaches are used to assay mediator release and to identify and manipulate proteins required for movement and exocytosis of secretory organelles.
organoleptic properties and molecular visualization of selected flavor materials.
Here we describe the results of a recent survey for molecular outflows associated with these clouds.
We are also investigating anaerobic methane oxidation using conventional and molecular techniques.
Characterized by the presence of free or molecular oxygen; requiring such conditions to live.
Molecular Computation Using DNA to solve computational problems can allow massive parallelism, by exploring 10 19 cases in parallel.
Guillain-BarrÃ© syndrome Investigating the molecular mechanisms causing nerve damage in Guillain-BarrÃ© Syndrome (which causes acute neuromuscular paralysis ).
paramagnetic organometallic compounds with the goal of trying to make a magnetically ordered molecular solid.
The molecular biology of helminth parasites (worms) is also under study in 3IR.
He was appointed to a Personal Chair in molecular parasitology in 1998.
Athens login off campus - see note at head of page MOLECULAR AND BIOCHEMICAL parasitology, from Swets 97- Access on and off campus.
Dr. Christophe Lacomme, of SCRI, whose interests include the molecular and cell biology of cereal pathogens.
Outline content: A lecture series will cover the basic principles of bacterial pathogenesis at the molecular level.
On a more basic level, we have an interest in the molecular pathogenesis of myeloma.
virus pathogenesis: - handout for molecular virology course.
His main research interest is the molecular pathology of cancer particularly the differential expressions of proteins.
Molecular basis of the coronary vascular actions of natriuretic peptides.
In the final year, you focus on analytical science biotechnology medicinal chemistry molecular pharmacology.
Further, molecular analyzes using different DNA cloning techniques will be applied to uncover the genetic lesions underlying the mutant phenotypes.
Professor Junia V. Melo has a longstanding interest in the molecular mechanisms underlying the malignant phenotype of CML.
Due to its relatively large molecular size, assays for acid phosphatase are serum or plasma based.
photochemistry of small molecules, for example HOCl, studied by molecular beam techniques.
We have examined the importance of isotope selective photodissociation / fractionation to gas mass estimation in molecular clouds.
This makes the use of molecular data vital for reconstructing louse phylogeny at this taxonomic level.
In addition, these sequence variations might be used for molecular phylogeny among these species.
Advances in the processing, sterilization, and cross-linking of ultrahigh molecular weight polyethylene for total joint arthroplasty.
The fibers are made from ultra high molecular weight polyethylene with an extremely high molecular mass.
He is now working on molecularly imprinted polymers and the rational design of polymers using molecular modeling and computational chemistry.
Figure 5: Molecular structure of cross linked polyethylene Addition and condensation polymers A very large number of monomers may be polymerized.
Molecular Dynamics Molecular dynamics is conceptually simple, yet extremely powerful.
presentation entitled: Osmoregulation at a molecular level in the bull shark, Carcharhinus leucas from the Brisbane River, Queensland.
The site is part of an optical microscopy primer from the Molecular Expressions site.
proteinaceous layer, and there are as yet few molecular markers.
pyrenoid structure remains elusive, whether formed from a starch sheath and/or proteinaceous layer, and there are as yet few molecular markers.
The higher resolution of large radio telescopes can be used to probe the structure of individual molecular clouds.
molecular rearrangement is a process by which Oh, I know Let's see.
Therefore, characterized GMO inserts are a very good model to study the molecular system involved in DNA rearrangements in general.
Molecular analysis of DNA junctions produced by illegitimate recombination in human cells.
Underlying molecular defect CF is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein.
The structure was solved by molecular replacement using the same protein solved in a different space group.
Early clinical studies and retinoid development commenced without an understanding of retinoid development commenced without an understanding of retinoid molecular biology.
Segregating sister genomes: the molecular biology of chromosome separation.
The molecular sieve with very large surface area accumulates water molecules from the gas stream.
The bottles are filled with molecular sieve material grade 542 crystalline aluminum silicate.
This finding is also supported by molecular dynamics simulations.
The structure was solved by molecular replacement using the same protein solved by molecular replacement using the same protein solved in a different space group.
Rebecca Wyand (JIC) investigated molecular host specificity in wild grass powdery mildew by screening a collection of isolates by ITS sequencing.
Many scientists do not share their pro-GM stance, and molecular geneticists are but a minute minority of all scientists.
steric clashes, we will need to run a short minimisation of this structure before starting molecular dynamics.
Gview recognizes the format of the molecular structure by the extension of the file.
The specific low molecular weight chondroitin sulfate, exclusive to Cosequin, is the most pure form available on the market.
The half-day symposium was entitled ' Molecular Approaches to Brain Disease ' and invited five neuroscience speakers to make presentations.
In 1999, we were awarded almost £ 500,000 to develop the study of the molecular systematics of marine organisms.
Jeff then followed with a review of the way in which molecular biological techniques are rapidly becoming tools of patient management.
Topics include: chemical thermodynamics, kinetic molecular theory, chemical kinetics, and statistical thermodynamics.
The electron microscope made this possible by playing the role of a " laboratory totem " for a growing tribe of molecular biologists.
He is also the founder of the European Workshop in molecular toxicology.
trajectoryRA menu holds a set of options that allow you to analyze GROMOS molecular dynamics trajectories.
ultra high molecular weight polyethylene with an extremely high molecular mass.
Research has also been conducted on aspects of molecular virology.
The manual divides comfortably without too much overlap into three sections, classical, molecular and medical virology.
Amazon.com and of course, not forgetting: Principles of Molecular virology A.J. Cann Provides an essential introduction to modern virology.
Partial anticoagulation with low molecular weight heparin (LMWH) or low dose warfarin (INR 1.5) are relative contraindications.
Typically, the molecular weight is measured using static light scattering.
Fischer next suggested that enzymes can only hydrolyse those sugars which possess a molecular structure in harmony with their own, or to use his ingenious analogy, "the one may be said to fit into the other as a key fits into a lock."
If Descartes had contented himself with thus explaining the phenomena of gravity, heat, magnetism, light and similar forces by means of the molecular movements of his vortices, even such a theory would have excited admiration.
He rejects the attempt to explain human personality as " generated by the material molecular aggregate of its own unaided latent power," and affirms that the " universe where the human spirit is more at home than it is among these temporary collocations of matter" is " a universe capable of infinite development, of noble contemplation, and of lofty joy, long after this planet - nay the whole solar system - shall have fulfilled its present spire of destiny, and retired cold and lifeless upon its endless way " (pp. 199-200).
Numerous other papers on molecular physics, including an experimental research on magnetism, appeared in the Proceedings of the Russian Academy of Science, the Physikalische Zeitschrift, the Proceedings of the German Physical Society, the Annalen der Physik, etc. (F.
There is some doubt as to the molecular formula of fulminic acid.
Boiling and freezing-point determinations of the molecular weight in solution indicate the formula S8.
This oxide exists in two forms. The aform is readily fusible and melts at 14.8Ã‚° C. It corresponds to the simple molecular complex S03.
The evolution of the notion of elements is treated under Element; the molecular hypothesis of matter under Molecule; and the genesis of, and deductions from, the atomic theory of Dalton receive detailed analysis in the article Atom.
A great advance was made by Dalton, who, besides introducing simpler symbols, regarded the symbol as representing not only the element or compound but also one atom of that element or compound; in other words, his symbol denoted equivalent weights.4 This system, which permitted the correct representation of molecular composition, was adopted by Berzelius in 1814, who, having replaced the geometric signs of Dalton by the initial letter (or letters) of the Latin names of the elements, represented a compound by placing a plus sign between the symbols of its components, and the number of atoms of each component (except in the case of only one atom) by placing Arabic numerals before the symbols; for example, copper oxide was Cu +0, sulphur trioxide S+30.
Laurent generally agreed, except when the theory compelled the adoption of formulae containing fractions of atoms; in such cases he regarded the molecular weight as the weight occupying a volume equal to four unit weights of hydrogen.
The development of the atomic theory and its concomitants - the laws of chemical combination and the notion of atoms and equivalents - at the hands of Dalton and Berzelius, the extension to the modern theory of the atom and molecule, and to atomic and molecular weights by Avogadro, Ampere, Dumas, Laurent, Gerhardt, Cannizzaro and others, have been noted.
In all cases it is usual to represent substances by formulae which to the best of our knowledge express their molecular composition in the state of gas, and not merely the relative number of atoms which they contain; thus, acetic acid consists of carbon, hydrogen and oxygen in the proportion of one atom of carbon, two of hydrogen, and one of oxygen, but its molecular weight corresponds to the formula C211402, which therefore is always employed to represent acetic acid.
When chemical change is expressed with the aid of molecular formulae not only is the distribution of weight represented, but by the mere inspection of the symbols it is possible to deduce from the law of gaseous combination mentioned above, the relative volumes which the agents and resultants occupy in the state of gas if measured at the same temperature and under the same pressure.
Formulae which merely express the relative number of atoms of the different elements present in a compound are termed empirical formulae, and the formulae of all compounds whose molecular weights are undetermined are necessarily empirical.
In addition to empirical and molecular formulae, chemists are in the habit of employing various kinds of rational formulae, called structural, constitutional or graphic formulae, &c., which not only express the molecular composition of the compounds to which they apply, but also embody certain assumptions as to the manner in which the constituent atoms are arranged, and convey more or less information with regard to the nature of the compound itself, viz.
(It will be noticed that Kolbe used the atomic weights H= 1, C=6, 0= 8, S = 16, &c.; his formulae, however, were molecular formulae, i.e.
A gas, therefore, has two specific heats, generally denoted by C p and C„, when the quantity of gas taken as a unit is one gramme molecular weight, the range of temperature being IÃ‚° C. It may be shown that Cp C„ = R, where R is the gas- constant, i.e.
The series H 2 S = - 61Ã‚°, CH 3 SH = 21 Ã‚°, (C 11 3) 2 S=41 Ã‚° is an example; in the first case, the molecular weight is increased and the symmetry diminished, the increase of boiling-point being 82Ã‚°; in the second case the molecular weight is again increased but the molecule assumes a more symmetrical configuration, hence the comparatively slight increase of 20Ã‚°.
The second and third causes, however, are of greater importance, since they are associated with the molecular condition of the substance; hence, it is obvious that it is only from some function of the refractive index which is independent of temperature variations and changes of state (i.e.
This subject has been principally investigated by Briihl; he found that molecular dispersions of liquids and gases were independent of temperature, and fairly independent of the state of aggregation, but that no simple connexion exists between atomic refractions and dispersions (see preceding table).
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