How to use Freezing-point in a sentence
The intermediate summits occurring in the freezing-point curves of alloys are usually rounded; this feature is believed to be due to the partial decomposition of the compound which takes place when it melts.
In the case of a pure substance, and of a certain small class of mixtures, there is no further fall in temperature until the substance has become completely solid, but, in the case of most mixtures, after the freezing-point has been reached the temperature soon begins to fall again, and as the amount of solid increases the temperature becomes lower and lower.
The summer temperature in the plains is that of southern Italy; in the mountain district& it is high during the day, but falls almost to freezing-point at night.
The communication between the Atlantic and Arctic basins being cut off, as already described, at a depth of about 300 fathoms, the temperatures in the Norwegian Sea below that level are essentially Arctic, usually below the freezing-point of fresh water, except where the distribution is modified by the surface circulation.
About the same time Davy showed that two pieces of ice could be melted by rubbing them together in a vacuum, although everything surrounding them was at a temperature below the freezing point.Advertisement
In the same way, whilst in the plains and hills round Naples snow is rarely seen, and never remains long, and the thermometer seldom descends to the freezing-point, 20 m.
For instance, suppose the effect of a falling temperature is to so modify the metabolism of the cells that they fill up more and more with watery sap; as the freezing-point is reached this may result in destructive changes, and death from cold may result.
Arctic plants make their brief growth and flower at a temperature little above freezing-point, and are dependent for their heat on the direct rays of the sun.
I have often seen the temperature in the Siberian steppes fall to more than forty degrees below freezing point !
Antifreeze will lower the freezing point of a liquid.Advertisement
Temperatures will drop into the 30s near the freezing point, 32 degrees Fahrenheit, although frost may form at temperatures slightly warmer than the freezing point.
Drink lots of water and prevent your water from freezing by adding flavor mix to it, which reduces the freezing point.
The temperature drops so rapidly that a month later, about October the oth on the middle Urals and November the 15th throughout Russia, the thermometer ceases to rise above the freezing-point.
The climate of Minas Geraes is characterized by high sun temperatures and cool nights, the latter often dropping below the freezing point on the higher campos.
The temperature is rather remarkable, there being an intermediate cold layer between 25 and 50 fathoms. This is due to the sinking of the cold surface water (which in winter reaches freezing-point) on to the top of the denser more saline water of the greater depths.Advertisement
Thermodynamic theory also indicates a connexion between the osmotic pressure of a solution and the depression of its freezing point and its vapour pressure compared with those of the pure solvent.
Thus the osmotic pressure, or the depression of the freezing point of a solution of potassium chloride should, at extreme dilution, be twice the normal value, but of a solution of sulphuric acid three times that value, since the potassium salt contains two ions and the acid three.
The freezing point curve usually lies below the electrical one, but approaches it as dilution is increased.2 Returning once more to the consideration of the first relation, which deals with the comparison between the number of ions and the number of pressure-producing particles in dilute solution, one caution is necessary.
Corresponding with this result we find that the freezing point of dilute solutions indicates that two pressure-producing particles per molecule are present.
If, however, this non-magnetic substance is cooled to a temperature a few degrees below freezing-point, it becomes as strongly magnetic as average cast-iron (µ = 62 for H = 40), and retains its magnetic properties indefinitely at ordinary temperatures.Advertisement
These limits may be set down as from a little above the freezing point of water to a little below the boiling point.
After this the metal is allowed to rest for a time in the pot at a temperature above its freezing point and is then ladled out into ingot forms, care being taken at each stage to ladle off the top stratum.
Soil whose temperature remains low, whether from its northerly aspect or from its high water content or other cause, is unsatisfactory, because the germination of seeds and the general life processes of plants cannot go on satisfactorily except at certain temperatures well above freezing-point.
This halt in the cooling, due to the heat evolved in the solidification of the first crystals that form in the liquid, is called the freezingpoint of the mixture; the freezing-point can generally be observed with considerable accuracy.
If we determine the freezing-points of a number of mixtures varying in composition from pure A to pure B, we can plot the freezing-point curve.Advertisement
In such a curve the percentage composition can be plotted horizontally and the temperature of the freezing-point vertically, as in fig.
In such a diagram, a point P defines a particular mixture, both as to percentage, composition and temperature; a vertical line through P corresponds to the mixture at all possible temperatures, the point Q being its freezing-point.
In the case of two substances which neither form compounds nor dissolve each other in the solid state, the complete freezing-point curve takes the form shown infig.5.
It consists of two branches AC and BC, which meet in a lowest point C. It will be seen that as we increase the percentage of B from nothing up to that of the mixture C, the freezing-point becomes lower and lower, but that if we further increase the percentage of B in the mixture, the freezing-point rises.
The two sloping lines cutting at the eutectic point are the freezing-point curves of alloys that, when they begin to solidify, deposit crystals of lead and tin respectively.Advertisement
Sometimes a freezing-point curve contains more than one intermediate summit, so that more than one compound is indicated.
Many other inter-metallic compounds have been indicated by summits in freezing-point curves.
Of these, the first three are well indicated on the freezing-point curves.
We must not take it for granted, when the freezing-point curve gives no indication of the compound, that the compound does not exist in the solid alloy.
For example, the compound Cu3Sn is not indicated in the freezing-point curve, and indeed a liquid alloy of this percentage does not begin to solidify by the formation of crystals of Cu 3 Sn; the liquid solidifies completely to a uniform solid solution, and only at a lower temperature does this change into crystals of the compound, the transformation being accompanied by a considerable evolution of heat.Advertisement
We can then draw a continuous surface through the summits of all these ordinates, and so obtain a freezing-point surface, or liquidus; points above this surface will correspond to wholly liquid alloys.
If now we cut the freezing-point surface by planes parallel to the base ABC we get curves giving us all the alloys whose freezing-point is the same; these isothermals can be projected on to the plane of the triangle and are seen as dotted lines in fig.
The freezing surface, in this case, consists of three sheets each starting from an angular point of the surface, that is, from the freezing-point of a pure metal.
The importance is now widely recognized of considering the mechanical properties of alloys in connexion with the freezing-point curves to which reference has already been made, but the subject is a very complicated one, and all that need be said here, is that when considered in relation to their meltingpoints the pure metals are consistently weaker than alloys.
Further Physical Properties of Sea-water.---The laws of physical chemistry relating to complex dilute solutions apply to seawater, and hence there is a definite relation between the osmotic pressure, freezing-point, vapour tension and boiling-point by which when one of these constants is given the others can be calculated.Advertisement
Experience shows that sea-water can be cooled considerably below the freezing-point without freezing if there is no ice or snow in contact with it.
Along the coast the average number of days during a year in which the temperature falls below freezing-point is only 3 or 4, but in the Panhandle this average is 111.
Along the coast the weather is very mild, the thermometer rarely falling to freezing-point even in winter.
In eastern Canada Ungava and Labrador are very chill and inhospitable, owing largely to the iceberg-laden current sweeping down the coast from Davis Strait, bringing fogs and long snowy winters and a temperature for the year much below the freezing-point.
Paschen proved that the emission spectra of water vapour as observed in an oxyhydrogen flame, and of carbon dioxide as observed in a hydrocarbon flame may be obtained by heating aqueous vapour and carbon dioxide respectively to a few hundred degrees above the freezing point.Advertisement
As early as 1788 Sir Charles Blagden (1748-1820) made measurements of the freezing points of salt solutions, and showed that the depression of freezing point was.
To take the simplest case of a one component system water substance has its three phases of solid ice, liquid water and gaseous vapour in equilibrium with each other at the freezing point of water under the pressure of its own vapour.
The phenomena of equilibrium can be represented on diagrams. Thus, if we take our co-ordinates to represent pressure and temperature, the state of the systems p with ice, water and vapour in equilibrium is represented by the point 0 where the pressure is that of the vapour of water at the freezing point and the temperature is the freezing point under that pressure.
If all the water be frozen, we have the vapour pressure curve of ice OB; while, if the pressure be raised, so that all the vapour vanishes, we get the curve OC of equilibrium between the pressure and the freezing point of water.
Equilibrium between these phases is obtained at the freezing point of the saturated solution under the pressure of the vapour.Advertisement
This constancy both in freezing point and composition formerly was considered as a characteristic of a pure chemical compound, and hence these mixtures were described as components and given the name of "cryohydrates."
If the process be continued till a very large quantity of ice be melted the resulting solution is so dilute that its freezing point B is identical with that of the pure solvent.
Or, by increasing the pressure, we eliminate the vapour and obtain the curve OF giving the relation between pressure, freezing point and composition when a saturated solution is in contact with ice and salt.
B is the freezing point of pure water, 0 that 2345 FIG.
This process continues till the composition of the liquid phase reaches that of the eutectic, when the whole mass solidifies on the further loss of heat without change of temperature, giving a very definite freezing point.
Thus in interpreting complicated freezing point curves, we must look for chemical compounds where the curve shows a maximum, and for a eutectic or cryohydrate where two curves meet at a minimum point.
At A we 66 have the freezing point of pure water, which is lowered by the gradual addition of 46 ferric chloride in the manner shown by the curve AB.
The theoretical form of the freezing point diagrams when solid solutions are present depends on the relation between the available energy and the composition in the two phases.
But at intermediate compositions we can only guess at the form of the energy-composition curve, and the freezing point composition curve, deduced from it, will vary according to the supposition which we make.
With the most likely forms for the energy curves we get the accompanying diagrams for the relation between freezing point and concentration.
All available evidence, from the freezing point curve and from other sources must be scrutinized before an opinion is pronounced.
Similar 'considerations show that, since at its freezing point the vapour pressure of a solution must be in equilibrium with that of ice, the depression of freezing point produced by dissolving a substance in water can be calculated from a knowledge of the vapour pressure of ice and water below the freezing point of pure water.
By imagining that a dilute solution is put through a thermodynamic cycle we may deduce directly relations between its osmotic pressure and its freezing point.
Let us Freezing freeze out unit mass of solvent from a solution at its freezing point T - dT and remove the ice, which is assumed to be the ice of the pure solvent.
Then let us heat both ice and solution through the infinitesimal temperature range dT to the freezing point T of the solvent, melt the ice by the application of an amount of heat L, which measures its latent heat of fusion, and allow the solvent so formed to enter the solution reversibly through a semi-permeable wall into an engine cylinder, doing an amount of work Pdv.
The freezing point of a solution may be determined experimentally.
The solution then freezes, until the heat liberated is enough to raise the tern perature to the point of equilibrium given by the tendency of the solution taken in contact with ice to approach the true freezing point on one side and the temperature of the enclosure on the other.
To get the true freezing point then, it is well to arrange that the temperature of the enclosure should finally be nearly that of the freezing point to be observed.
But we have seen that the depression of dT of the freezing point of a dilute solution is measured by TPdv/L.
Dilute solutions of substances such as cane-sugar, as we have seen, give experimental values for the connected osmotic properties - pressure, freezing point and vapour pressure - in conformity with the theoretical values.
The slope of the temperature vapour pressure curves in the neighbourhood of the freezing point of the solvent is given by the latest heat equation.
Approximately one degree lowering of freezing point corresponds with a change of 12 atmospheres in the osmotic pressure.
Thus the theory of the connexion of osmotic pressure with freezing point (like that with vapour pressure) seems to give results which accord with experiments.
Whether osmotic pressure be due to physical impact or to chemical affinity it must necessarily have the gas value in a dilute solution, and be related to vapour pressure and freezing point in the way we have traced.
Snow is often seen, and the thermometer is frequently below freezing-point.
There, a sun which never sets sends feeble rays that maintain a low equable temperature, rarely rising more than a few degrees above the freezing-point.
The temperature of the cold chamber is varied from the freezing-point of water, to a few degrees lower, according to the needs of the plants under treatment.
The Greenhouse is a structure designed for the growth of such exotic plants as require to be kept during winter in a temperature considerably above the freezing-point.
These freezing-point curves and transformation curves thus divide the diagram into 8 distinct regions, each with its own specific state or constitution of the metal, the molten state for region 1, a mixture of molten metal and of solid austenite for region 2, austenite alone for region 4 and so on.
But, far below the freezing-point, transformations may take place in the solid metal, and follow a course quite parallel with that of freezing, though with no suggestion of liquidity.
Thus the iron has rather a freezingrange than a freezing-point.
The mean summer temperature there is 66 and upwards, while the average temperature of January does not descend to the freezing point (32).
In only seven of the thirty years, 1871-1900, was the thermometer observed to sink below the freezing-point; frost thus occurs in the island even on the low grounds, though never for more than a few hours.
But in many cases it is more readily determined by observing the rise of the boiling-point or the depression of the freezing-point of the solution.
For the depression of the freezing-point a relation of the same form applies, but do is negative, and L is the latent heat of fusion.
At the freezing-point, the solution must have the same vapour-pressure as the solid solvent, with which it is in equilibrium.
The relation follows immediately from Kirchhoff's expression (below, section 14) for the difference of vapour-pressure of the liquid and solid below the freezing-point.
The highest pressures recorded for cane-sugar are nearly three times as great as those given by van't Hoff's formula for the gas-pressure, but agree very well with the vapour-pressure theory, as modified by Callendar, provided that we substitute for V in Arrhenius's formula the actual specific volume of the solvent in the solution, and if we also assume that each molecule of sugar in solution combines with 5 molecules of water, as required by the observations on the depression of the freezing-point and the rise of the boiling-point.
Although the temperature remains pretty steadily below the freezing point for at least three months of the year, many of the harbours remain unobstructed; for the tides and the prevailing off-shore winds break up and drive off the ice.
Again in the plateau regions in the south the night temperature is sometimes down to freezing point.
The lake never freezes over, though the temperature of the water does not, even in summer, rise far above freezing point.
The graduation of a thermometer is determined by the freezing-point and the boiling-point of water, the interval between these being divided into a certain number of degrees, representing equal increases of temperature.
Ice forms over fresh water if the temperature of the air has been for a sufficient time at or below the freezing-point; but not until the whole mass of water has been cooled down to its point of maximum density, so that the subsequent cooling of the surface can give rise to no convection currents, is freezing possible.
In this zone there prevails a genuine sub-tropical climate, with extremely warm and almost rainless summers and mild winters, the temperature hardly ever sinking below freezing-point.
The pressure being still further reduced, the temperature is gradually lowered until the freezing-point is reached and ice formed, when about one-sixth of the original volume has been evaporated.
The rabbit flea can live for nine months at temperatures around the freezing point without feeding.
Around the coast the weather can be surprisingly mild, regularly reaching freezing point in summer.
I have often seen the temperature in the Siberian steppes fall to more than forty degrees below freezing point!
Boiling and freezing-point determinations of the molecular weight in solution indicate the formula S8.
At present, measurements of freezing point are more convenient and accurate than those of osmotic pressure, and we may test the validity of Arrhenius' relations by their means.
The region PbEeE' contains all the alloys that commence their solidification by the crystallization of lead; similarly, the other two regions correspond to the initial crystallization of bismuth and tin respectively; these areas are the projections of the three sheets of the freezing-point surface.
The well-known expression for the efficiency of the cycle of reversible operation gives us Pdv/L = dT /T or dT = TPdv/L as a value for the depression of the freezing point of the solution compared with that of the pure solvent.
If this course is inconvenient, some liquid of low freezing-point, such as glycerine, may be mixed with the water.