Crystals of azurite belong to the monoclinic system; they have a vitreous lustre and are translucent.

It forms monoclinic crystals which are very soluble in water.

The crystals of prismatic habit represented in figs.

The crystals are feebly doubly refracting, and in polarized light exhibit a banded structure parallel to the cube faces.

With deadly accuracy, she threw the ball at him, laughing when it bounced off his leather coat and sprayed a mist of white crystals in his face.

It separates in the form of small rose-red crystals, which decompose on boiling with water.

Crystals are prismatic, acicular or scaly in habit; they have a perfect cleavage parallel to the brachypinacoid (M in the figure).

Cesena and Perticara are well-known localities in this district, the latter yielding crystals coated with asphalt.

Mountain winters were always a surprise to lowlanders and easterners, where the chemistry of moisture played games that produced slush and wet snow, not the sparkling crystals so soft a broom could clear a foot-deep snowfall with a few swishes.

Boron dissolves in molten aluminium, and on cooling, transparent, almost colourless crystals are obtained, possessing a lustre, hardness and refractivity near that of the diamond.

Crystals have the form of small, sharply defined cubes of an oliveor grass-green colour, and occur together in considerable numbers on the matrix of the specimens.

These are, according to Meyer, acicular crystals, which he calls tricizites.

Fine crystals occur at Conil near Cadiz; whilst in the province of Teruel in Aragon, sulphur in a compact form replaces fresh-water shells and plant-remains, suggesting its origin from sulphur-springs.

The solution obtained may be evaporated in vacuo until it attains a density of 1.46 when, if partially saturated with potassium hydroxide and filtered, it yields crystals of potassium pentathionate, K 2 S 5 0 6.3H 2 0.

Beautiful rock crystals occur in veins in the corries.

Albumen crystals are also to be found in the cytoplasm, in leucoplasts and rarely in the nucleus.

as crystals, and as stalactitic, encrusting, reniform, massive, earthy and occasionally pulverulent forms as "sulphur meal."

Each cell contains a zinc plate, immersed in a solution of zinc sulphate, and also a porous chamber containing crystals of copper sulphate and a copper plate.

Crystals of sulphur are transparent or translucent and highly refractive with strong birefringence; they have a resinous or slightly adamantine lustre, and present the characteristic sulphur-yellow colour.

They form yellow or bronze-coloured crystals, which decompose on boiling their aqueous solution.

Natural crystals are sometimes honey-yellow to brown in colour, but this appears to be due to alteration.

Light snow had begun to fall—tiny crystals hardly visible in the light of the lamp across the street.

The most important subjects of his inquiries are enumerated by Forbes under the following five heads: - (1) The laws of polarization by reflection and refraction, and other quantitative laws of phenomena; (2) The discovery of the polarizing structure induced by heat and pressure; (3) The discovery of crystals with two axes of double refraction, and many of the laws of their phenomena, including the connexion of optical structure and crystalline forms; (4) The laws of metallic reflection; (5) Experiments on the absorption of light.

Crystals were first found in Cornwall (at Wheal Jane, near Truro, associated with pyrrhotite) by J.

It forms dark red crystals isomorphous with ferrous sulphate, and readily soluble in water.

Of the suspended substances, grains of caoutchouc, drops of resin and oil, proteid crystals and starch grains may be mentioned.

Free sulphur may also result from the decomposition of pyrites, as in pyritic shales and lignites, or from the alteration of galena: thus crystals of sulphur occur, with anglesite, in cavities in galena at Monteponi near Iglesias in Sardinia; whilst the pyrites of Rio Tinto in Spain sometimes yield sulphur on weathering.

In this line of investigation the prime importance belongs to the discovery (1) of the connexion between the refractive index and the polarizing angle, (2) of biaxial crystals, and (3) of the production of double refraction by irregular heating.

Crystals of barytes are orthorhombic and isomorphous with the strontium and lead sulphates (celestite and anglesite); they are usually very perfectly developed and present great variety of form.

Barytes is of common occurrence in metalliferous veins, especially those which yield ores of lead and silver; some of the largest and most perfect crystals of colourless barytes were obtained from the lead mines near Dufton in Westmorland.

It is found also in beds of iron ore, and the haematite mines of the Cleator Moor district in west Cumberland have yielded many extremely fine crystals, specimens of which may be seen in all mineral collections.

In the neighbourhood of Nottingham, and other places in the Midlands, barytes forms a cementing material in the Triassic sandstones; amber-coloured crystals of the same mineral are found in the fuller's earth at Nutfield in Surrey; and the septarian nodules in London Clay contain crystals of barytes as well as of calcite.

Crystals are found as a rarity in the amygdaloidal cavities of igneous rocks.

Artificially prepared crystals of barytes may be obtained by allowing a solution of a soluble barium salt to diffuse slowly into a solution of a soluble sulphate.

Crystals of a different form are deposited from a strong boiling solution of the acid.

It forms very hard metallic-looking crystals, burns in oxygen and is not attacked by acids.

It forms silky crystals which melt at 6° C., and boil at about 144° C. with decomposition.

They are composed of a homogeneous proteid substance, and often contain albuminoid or proteid crystals of the same kind as those which form the pyrenoid.

- On the theory that crystal form and structure are the result of the equilibrium between the atoms and molecules composing the crystals, it is probable, a priori, that the same substance may possess different equilibrium configurations of sufficient stability, under favourable conditions, to form different crystal structures.

In the article Crystallography the nature and behaviour of twinned crystals receives full treatment; here it is sufficient to say that when the planes and axes of twinning are planes and axes of symmetry, a twin would exhibit higher symmetry (but remain in the same crystal system) than the primary crystal; and, also, if a crystal approximates in its axial constants to 'a higher system, mimetic twinning would increase the approximation, and the crystal would be pseudo-symmetric.

White Pond and Walden are great crystals on the surface of the earth, Lakes of Light.

Gabriel took the crystals with a nod.

Pharmacosiderite is a mineral of secondary origin, the crystals occurring attached to gozzany quartz in the upper part of veins of copper ore.

Sammetblende or przibramite is a variety, from Przibram in Bohemia, consisting of delicate acicular or capillary crystals arranged in radiating groups with a velvety surface and yellow colour.

A sublimate may be formed of: sulphur - reddish-brown drops, cooling to a yellow to brown solid, from sulphides or mixtures; iodine - violet vapour, black sublimate, from iodides, iodic acid, or mixtures; mercury and its compounds - metallic mercury forms minute globules, mercuric sulphide is black and becomes red on rubbing, mercuric chloride fuses before subliming, mercurous chloride does not fuse, mercuric iodide gives a yellow sublimate; arsenic and its compounds - metallic arsenic gives a grey mirror, arsenious oxide forms white shining crystals, arsenic sulphides give reddish-yellow sublimates which turn yellow on cooling; antimony oxide fuses and gives a yellow acicular sublimate; lead chloride forms a white sublimate after long and intense heating.

It is decomposed by water, and with a solution of yellow phosphorus in carbon bisulphide it gives a red powder of composition PBI 2, which sublimes in vacuo at 210° C. to red crystals, and when heated in a current of hydrogen loses its iodine and leaves a residue of boron phosphide PB.

It forms slightly coloured small crystals possessing a strong disagreeable smell, and is rapidly decomposed by water with the formation of boric acid and sulphuretted hydrogen.

Cadmium sulphate, CdSO 4, is known in several hydrated forms; being deposited, on spontaneous evaporation of a concentrated aqueous solution, in the form of large monosymmetric crystals of composition 3CdSO 4.8H 2 O, whilst a boiling saturated solution, to which concentrated sulphuric acid has been added, deposits crystals of composition CdSO 4 4H 2 0.

The sun knows that you like to see the world covered with beautiful white snow and so he kept back all his brightness, and let the little crystals form in the sky.

Kris slid two rare green life crystals across the table, the common form of payment for an assassination not ordered by Death herself.

The ceilings were gilded, the chandeliers dripping with crystals.

By either of these methods, it is obtained in the form of bronzecoloured crystals.

The liquid is precipitated by alcohol, and the washed and dried precipitate is then dissolved in water and allowed to stand, when the salt separates in dark-coloured crystals.

Starch grains may often be seen in contact with the pigment crystals.

It is the methyl ester of a neutral body colchicein, which may be obtained in white acicular crystals.

The potassium salt, after recrystallization from warm water, separates in large tabular crystals.

There have been repeated stories of diamonds obtained from the Finley Mountains (which are volcanic) in the central province, but all specimens sent home, except one, have hitherto proved to be quartz crystals.

Westward to Houston and southward to about 32° 48' on the Alabama boundary and occupying a much larger area than the other Cretaceous formations, is the Selma chalk, called "Rotten Limestone" by Hilgard; it is made up of a material of great uniformity, - a soft chalky rock, white or pale blue, composed chiefly of tenacious clay, and white carbonate of lime in minute crystals.

The "crested" or "cock's comb" barytes occurs as rounded aggregations of thin lamellar crystals.

All these are strikingly alike in appearance and general characters, differing essentially only in chemical composition, and it would seem better to reserve the name cerargyrite for the whole group, using the names chlorargyrite (AgC1), embolite (Ag(Cl, Bl)), bromargyrite (AgBr) and iodembolite (Ag(C1, Br, I)) for the different isomorphous members of the group. They are cubic in crystallization, with the cube and the octahedron as prominent forms, but crystals are small and usually indistinct; there is no cleavage.

A crystal may be regarded as built up of primitive parallelepipeda, the edges of which are in the ratio of the crystallographic axes, and the angles the axial angles of the crystals.

While polysymmetry is solely conditioned by the manner in which the mimetic twin is built up from the single crystals, there being no change in the scalar properties, and the vector properties being calculable from the nature of the twinning, in the case of polymorphism entirely different structures present themselves, both scalar and vector properties being altered; and, in the present state of our knowledge, it is impossible to foretell the characters of a polymorphous modification.

When precipitated from solutions it forms red tetragonal crystals, which, on careful heating, give a yellow rhombic form, also obtained by crystallization from the fused substance, or by sublimation.

Hexachlorethane is trimorphous, forming rhombic, triclinic and cubic crystals; the successive changes occur at about 44° and 71°, and are attended by a decrease in density.

Lehmann it melts at 168° (or at a slightly lower temperature in its water of crystallization) and on cooling forms optically isotropic crystals; at 125.6° the mass becomes doubly refracting, and from a solution rhombohedral (optically uniaxial) crystals are deposited; by further cooling acicular rhombic crystals are produced at 82.8°, and at 32.4° other rhombic forms are obtained, identical with the product obtained by crystallizing at ordinary temperatures.

telluric acid forms cubic and monoclinic crystals from a hot nitric acid solution, and ammonium fluosilicate gives cubic and hexagonal forms from aqueous solutions between 6° and 13°.

Many instances have been recorded where substitution has effected a deformation in one particular direction, the crystals of homologous compounds often exhibiting the same angles between faces situated in certain zones.

More useful is the property of isomorphous substances of forming mixed crystals, which are strictly isomorphous with their constituents, for all variations in composition.

In such crystals each component plays its own part in determining the physical properties; in other words, any physical constant of a mixed crystal can be calculated as additively composed of the constants of the two components.

8 shows the variation of refractive index of mixed crystals of potash alum and thallium alum with variation in composition.

In these two instances the component crystals are miscible in all proportions; but this is by no means always the case.

It may happen that the crystals do not form double salts, and are only miscible in certain proportions.

Two cases then arise: (I) the properties may be expressed as linear functions of the composition, the terminal values being identical with those obtained for the individual components, and there being a break in the curve corresponding to the absence of mixed crystals; or (2) similar to (I) except that different values must be assigned to the terminal values in order to preserve collinearity.

9 illustrates the first case: the ordinates represent specific volumes, and the abscissae denote the composition of isomorphous mixtures of ammonium and potassium dihydrogen phosphates, which mutually take one another up to the extent of 20% to form homogeneous crystals.

Magnesium sulphate (orthorhombic) takes up ferrous sulphate (monoclinic) to the extent of 19%, forming isomorphous orthorhombic crystals; ferrous sulphate, on the other hand, takes up magnesium sulphate to the extent of 54% to form monoclinic crystals.

By plotting the specific volumes of these mixed crystals as ordinates, it is found that they fall on two lines, the upper corresponding to the orthorhombic crystals, the lower to the monoclinic. From this we may conclude that these salts are isodimorphous: the upper line represents isomorphous crystals of stable orthorhombic magnesium sulphate and unstable orthorhombic ferrous sulphate, the lower line isomor phous crystals of stable monoclinic ferrous sulphate and unstable monoclinic magnesium sulphate.

An important distinction separates true mixed crystals and crystallized double salts, for in the latter the properties are not linear functions of the properties of the components; generally there is a contraction in /10.591 volume, while the re fractive indices and other physical properties do not, in general, obey the additive law.

He also engaged in work on magnetism, the polarization of light, phosphorescence and the absorption of light in crystals.

Babingtonite is found as small black crystals on felspar in the granite of Baveno in Italy, and in the Haytor iron mine in Devonshire.

It forms a mass of deep blue crystals at the temperature of liquid air.

When heated with CS 2 to 1 00° C. under pressure, it forms liquid nitrogen sulphide, N 2 S 5, a mobile red liquid which solidifies to an iodine-like mass of crystals which melt at Io-I I° C. Water, alkalis and acids decompose it into sulphur and ammonia (W.

There are, therefore, a number of agencies, all of which operate in shoal waters on the lee side of islands, or in shallow lagoons in such regions as the Bahamas, and the result of all these is to throw down calcium carbonate from solution in sea-water as minute needle-shaped crystals or little balls of aragonite.

Rhyolitic lavas frequently are more or less vitreous, and when the glassy matter greatly predominates and the; crystals are few and inconspicuous the rock becomes an obsidian; the chemical composition is essentially the same as that of granite; the difference in the physical condition of the two rocks is due to the fact that one consolidated at the surface, rapidly and under low pressures, while the other cooled slowly at great depths and under such pressures that the escape of the steam and other gases it contained was greatly impeded.

Few obsidians are entirely vitreous; usually they have small crystals of felspar, quartz, biotite or iron oxides, and when these are numerous the rock is called a porphyritic obsidian (or hyalo-liparite).

These crystals have, as a rule, very good crystalline form, but the quartz and felspar are often filled with enclosures of glass.

Their lustre is vitreous except when they contain many minute crystals; they are then velvety or even resinous in appearance.

When crystals are present they generally have their long axes parallel to the fluxion.

Even when conspicuous and well formed crystals are not visible in the rock there is nearly always an abundance of minute imperfect crystallizations (microlites, &c.).

The larger ones polarize light, have angular outlines like those of crystals, and may even show twinning and definite optical properties by which they can be identified as belonging to felspar, augite or some other rock-forming mineral.

Porphyritic crystals often contract less than the surrounding glass, which accordingly becomes strained, and in polarized light may show a weak double refraction in a limited area surrounding the crystal.

Occasionally the rounded cracks extend from the matrix into some of the crystals especially those of quartz which have naturally a conchoidal fracture.

By many lines of evidence we are led to believe that obsidians in course of time suffer devitrification, in other words they pass from the vitreous into a crystalline state, but as the changes take place in a solid mass they require a very long time for their achievement, and the crystals produced are only of extremely small size.

They all crystallize in the monoclinic system, often, however, in forms closely resembling those of the rhombohedral or orthorhombic systems. Crystals have usually the form of hexagonal or rhomb-shaped scales, plates or prisms, with plane FIG.

The best developed crystals are those of Vesuvian biotite.

Flattened crystals of garnet, films of quartz, and needles of tourmaline are not uncommon.

Artificially formed crystals of the various species of mica have been observed in furnace-slags and in silicate fusions.

The best crystallized specimens of any mica are afforded by the small brilliant crystals of biotite, which encrust cavities in the limestone blocks ejected from Monte Somma, Vesuvius.

This resolution of the original wave is the well-known "Principle of Huygens," and by its means he was enabled to prove the fundamental laws of optics, and to assign the correct construction for the direction of the extraordinary ray in uniaxial crystals.

The crystals of impoverished lead which fall process.

To the kettle, two-thirds full of crystals of lead, is now added lead of the same tenor in silver, the whole is liquefied, and the cooling, crystallizing, skimming and ladling are repeated.

This cools and stirs the lead when crystals begin to form.

As soon as two-thirds of the lead has separated in the form of crystals, the steam is shut off and the liquid lead drained off through the two spouts into the moulds.

The fire underneath the pot is again started, the crystals are liquefied, and one of the two pans, filled with melted lead, is tilted by means of the crane and its contents poured into the pot.

Lead nitrate, Pb(N03)2, is obtained by dissolving the metal or oxide in aqueous nitric acid; it forms white crystals, difficultly soluble in cold water, readily in hot water and almost insoluble in strong nitric acid.

It forms colourless transparent crystals, soluble in one and a half parts of cold water and in eight parts of alcohol, which on exposure to ordinary air become opaque through absorption of carbonic acid, which forms a crust of basic carbonate.

It crystallizes from water in large rhombic crystals, which melt at 118° C. Oxidizing agents convert it into benzaldehyde.

In anisotropic bodies, such as crystals, the direction of the magnetization does not in general coincide with that of the magnetic force.

He also showed that crystals of alum cannot be obtained by dissolving alumina in sulphuric acid and evaporating the solutions, but when a solution of potash or ammonia is dropped into this liquid, it immediately deposits perfect crystals of alum (Sur la regeneration de l'alun, Marggraf's Opusc. ii.

Knowing that alum cannot be obtained in crystals without the addition of potash, he began to suspect that this alkali constituted an essential ingredient in the salt, and in 1797 he published a dissertation demonstrating that alum is a double salt, composed of sulphuric acid, alumina and potash (Annales de chimie, xxii.

The solution turns yellow in colour, and, when saturated, deposits a pasty mass of crystals.

These are filtered off hot, and the filtrate is allowed to cool, when crystals of the uranate separate out.

The solution in sulphuric acid deposits green crystals of the sulphate, U(S04)2.8H20, on evaporation.

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.

According to Stolba, beautiful crystals of pure tin can be obtained as follows: A platinum basin, coated over with wax or paraffin outside, except a small circle at the very lowest point, is placed on a plate of amalgamated zinc, lying on the bottom of a beaker, and is filled with a solution of pure stannous chloride.

The whole is then left to itself, when crystals of tin gradually separate out on the bottom of the basin.

This structure can be rendered visible by superficial etching with dilute acid; and as the minuter crystals dissolve more quickly than the larger ones, the surface assumes a frosted appearance (moiree metallique).

The metal is dimorphous: by cooling molten tin at ordinary air temperature tetragonal crystals are obtained, while by cooling at a temperature just below the melting point rhombic forms are produced, When exposed for a sufficient time to very low temperatures (to - 39° C. for 14 hours), tin becomes so brittle that it falls into a grey powder, termed the grey modification, under a pestle; it indeed sometimes crumbles into powder spontaneously.

The chloride readily combines with water to form a crystallizable hydrate SnCl 2.2H 2 O, known as "tin salt" or "tin crystals."

The crystals are very soluble in cold water, and if the salt is really pure a small proportion of water forms a clear solution; but on adding much water most of the salt is decomposed, with the formation of a precipitate of oxychloride, 2Sn(OH)Cl H20.

According to Michel and Kraft, one litre of cold saturated solution of tin crystals weighs 1827 grammes and contains 1333 grammes of SnCl 2.

The same oxychloride is produced when the moist crystals, or their solution, are exposed to the air.

Hence all tin crystals as kept in the laboratory give with water a turbid solution, which contains stannic in addition to stannous chloride.

A strip of metallic zinc when placed in a solution of stannous chloride precipitates the tin in crystals and takes its place in the solution.

The haematoidin pigment may vary in colour from yellowish or orange-red to a ruby-red, and forms granular masses, rhombic prisms or acicular crystals.

These crystals are extremely resistant to absorption, are found in old blood clots, and have been known to persist in old cerebral haemorrhages after many years.

He also devoted much attention to the pyroelectric phenomena of crystals, which served as the theme of one of the two memoirs he presented for the degree of D.Sc. in 1869, and to the determination of crystallographic constants.

It forms white crystals, which melt at 40° C., and are readily soluble in water, alcohol and ether.

" glare," " glow "), a hard substance, usually transparent or translucent, which from a fluid condition at a high temperature has passed to a solid condition with sufficient rapidity to prevent the formation of visible crystals.

A similar glass, if its cooling is greatly retarded, produces throughout its substance minute crystals of metallic copper, and closely resembles the mineral called avanturine.

The refractive indices of all glasses at present available lie between 1.46 and 1 90, whereas transparent minerals are known having refractive indices lying considerably outside these limits; at least one of these, fluorite (calcium fluoride), is actually used by opticians in the construction of certain lenses, so that probably progress is to be looked for in a considerable widening of the limits of available optical materials; possibly such progress may lie in the direction of the artificial production of large mineral crystals.

From the alloy containing 25% of silicon, the excess of magnesium is removed by a mixture of ethyl iodide and ether and a residue consisting of slate-blue octahedral crystals of magnesium silicide is left.

These frozen metals in general form compact masses consisting of aggregates of crystals belonging to the regular or rhombic or (more rarely) the quadratic system.

The crystals belong to the following systems: regular system - silver, gold, palladium, mercury, copper, iron, lead; quadratic system - tin, potassium; rhombic system - antimony, bismuth, tellurium, zinc, magnesium.

Gold, silver, copper, lead, aluminium, cadmium, iron (pure), nickel and cobalt are practically amorphous, the crystals (where they exist) being so closely packed as to produce a virtually homogeneous mass.

form rhombic or quadratic crystals.

Regular crystals expand equally in all directions; rhombic and quadratic expand differently in different directions.

Hence, supposing the crystals immediately after their formation to be in absolute contact with one another all round, then, in the case of Class II., such contact will be maintained on cooling, while in the case of Class I.

the contraction along a given straight line will in general have different values in any two neighbouring crystals, and the crystals consequently become slightly detached from one another.

It may be solidified to rhombic crystals which melt at 5.4° C. (Mansfield obtained perfectly pure benzene by freezing a carefully fractionated sample.) It boils at 80 4°, and the vapour is highly inflammable, the flame being extremely smoky.

The curing or preparation of the crystals for the market by separating the molasses from them.

It is found that in reducing the juice of these two qualities to syrup, fit to pass to the vacuum pans for cooking to crystals, the total amount of evaporation from the degraded j uice is about half that required from the normal juice produced by double crushing.

The choice of the size of the crystals to be produced in a given pan depends upon the market for which they are intended.

The crystallized sugar from the vacuum pan has now to be separated from the molasses or mother-liquor surrounding the crystals.

The moisture from the clay, percolating through the mass of sugar, washes away the adhering molasses and leaves the crystals comparatively free and clear.

Thus also the crystals already formed come in contact with fresh mother-liquor, and so go on adding to their size.

The use of multiple-effect evaporation made it possible to raise the steam for all the work required to be done in a well-equipped factory, making crystals, under skilful management, by means of the bagasse alone proceeding from the.

The filtered liquors, being collected in the various service tanks according to their qualities, are drawn up into the vacuum pans and boiled to crystals.

Granulated sugar, so called, is made by passing the crystals, after leaving the centrifugals, through a large and slightly inclined revolving cylinder with a smaller one inside heated by steam.

The firstmentioned process consists of charging and feeding the vacuum pan with the richest syrup, and then as the crystals form and this syrup becomes thereby less rich the'pan is fed with syrup of lower richness, but still of a richness equal to that of the mother-liquor to which it is added, and so on until but little mother-liquor is left, and that of the poorest quality.

Suitable provision is made for the egress of syrup from the massecuite in the cells when undergoing purging in the centrifugal; and the washing of the crystals can be aided by the injection of refined syrup and completed by that of " clairce."

As found in nature, saltpetre generally forms aggregates of delicate acicular crystals, and sometimes silky tufts; distinctly developed crystals are not found in nature.

When crystallized from water, crystals belonging to the orthorhombic system, and having a prism angle of 61 0 10', are obtained; they are often twinned on the prism planes, giving rise to pseudo-hexagonal groups resembling aragonite.

The caliche is worked up in loco for crude nitrate by extracting the salts with hot water, allowing the suspended earth to settle, and then transferring the clarified liquor, first to a cistern where it deposits part of its sodium chloride at a high temperature, and then to another where, on cooling, it yields a crop of crystals of purified nitrate.

It forms colourless, transparent rhombohedra, like those of Iceland spar; the angles are nearly equal to right angles, being 73° 30', so that the crystals look like cubes: hence the name of "cubic saltpetre."

There are perfect cleavages parallel to the rhombohedral faces, and the crystals exhibit a strong negative double refraction, like calcite.

It fuses at 415° C. and under ordinary atmospheric pressure boils at 1040° C. Its vapour density shows that it is monatomic. The molten metal on cooling deposits crystals belonging to the hexagonal system, and freezes into a compact crystalline solid, which may be brittle or ductile according to circumstances.

At Ioo° C. the crystals lose 6 of their molecules of water; the remaining molecule goes off at 250°, a temperature which lies close to that at which the salt begins to decompose.

In 1822 Wollaston examined a specimen of those beautiful copper-like crystals which are occasionally met with in iron-furnace slags, and declared them to be metallic titanium.

This view had currency until 1849, when Wohler showed that the crystals are a compound, Ti(CN)2.3T13N2, of a cyanide and a nitride of the metal.

The crystals are collected, washed, pressed and recrystallized, whereby the impurities are easily removed.

Titanium monoxide, TiO, is obtained as black prismatic crystals by heating the dioxide in the electric furnace, or with magnesium powder.

The ordinary hydrated variety forms quadratic crystals and behaves as a strong base.

It forms deliquescent crystals, which are readily soluble in alcohol and melt at ioo° C. When heated for some time at 130° C. it yields fumaric acid (q.v.), and on rapid heating at 180° C. gives maleic anhydride and fumaric acid.

Thus, for instance, near Nikko in the upper valley of the Daiya-gawa, and in several other places in the neighboring mountains, a granite-porphyry appears with large, pale, flesh-colored crystals of orthoclase, dull triclinic feispar, quartz and hornblende.

From the mine of Ichinokawa in Shikoku come the wonderful crystals of antimonite, which form such conspicuous objects in the mineralogical cabinets of Europe.

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.

All the mixtures whose composition lies between that of A and C deposit crystals of pure.

A when they begin to solidify, while mixtures between C and B in composition deposit crystals of pure B.

As it cools from P to Q the mixture remains wholly liquid, but when 200 the temperature Q is reached there is a halt in the cooling, due to the formation of crystals loo° of A.

The cooling soon recommences and these crystals continue to form, but at lower and o°c lower temperatures because the still liquid part is becoming richer in B.

This process goes on until the state of the remaining liquid is represented by the point C. Now crystals of B begin to form, simultaneously with the A crystals, and the composition of the remaining liquid does not alter as the solidification progresses.

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.

eutectic point gives the second halt in cooling, due to the simultaneous formation of lead crystals and tin crystals.

In the case of this pair of metals, or indeed of any metallic alloy, we cannot see the crystals forming, nor can we easily filter them off and examine them apart from the liquid, although this has been done in a few cases.

If we examine alloys on the tin side we shall find large crystals of tin embedded in the same complex.

We can sometimes obtain definite compounds in a pure state by the action of appropriate solvents which dissolve the rest of the alloy and do not attack the crystals of the compound.

It is probable that all the alloys of compositions between B and D, when they begin to solidify, deposit crystals of the compound; the lower eutectic B probably corresponds to a solid complex of mercury and the compound.

It also possesses a splendid purple Here, the large dark masses are the silver or silver-rich substance that crystallized above the eutectic temperature, and the more minute black and white complex represents the eutectic. It is not safe to assume that the two ingredients we see are pure silver and pure copper; on the contrary, there is reason to think that the crystals of silver contain some copper uniformly diffused through them, and vice versa.

We thus learn that the bronzes referred to above, although chemically uniform when solid, are not so when they begin to solidify, but that the liquid deposits crystals richer in copper than itself, and therefore that the residual liquid becomes richer in tin.

Consequently, as the final solid is uniform, the crystals formed at first must change in composition at a later stage.

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.

Alloys represented by points on Ee, when they begin to solidify, deposit crystals of lead and bismuth simultaneously; Ee is a eutectic line, as also are E'e and E"e.

Among objects used are a pool of ink in the hand (Egypt), the liver of an animal (tribes of the North-West Indian frontier), a hole filled with water (Polynesia), quartz crystals (the Apaches and the Euahlayi tribe of New South Wales), a smooth slab of polished black stone (the Huille-che of South America), water in a vessel (Zulus and Siberians), a crystal (the Incas), a mirror (classical Greece and the middle ages), the finger-nail, a swordblade, a ring-stone, a glass of sherry, in fact almost anything.

Owing to the softness of the metal, large crystals are rarely well defined, the points being commonly rounded.

Except in the larger nuggets, which may be more or less angular, or at times even masses of crystals, with or without associated quartz or other rock, gold is generally found bean-shaped or in some other flattened form, the smallest particles being scales of scarcely appreciable thickness, which, from their small bulk as compared with their surface, subside very slowly when suspended in water, and are therefore readily carried away by a rapid current.

With 10% of gold present the amalgam is fluid, and with 12.5% pasty, while with 13% it consists of yellowish-white crystals.

Matthiessen and Bose obtained large crystals of the alloy Au 2 Sn 5, having the colour of tin, which changed to a bronze tint by oxidation.

By crystallizing an aqueous solution, red crystals of AuC1 3.2H 2 O are obtained.

Aurous bromide, AuBr, is a yellowish-green powder obtained by heating the tribromide to 140°; auric bromide, AuBr 3, forms reddish-black or scarlet-red leafy crystals, which dissolve in water to form a reddishbrown solution,and combines with bromides to form bromaurates corresponding to the chloraurates.

The acid, auricyanic acid, 2HAu (CN) 4.3H20, is obtained by treating the silver salt (obtained by precipitating the potassium salt with silver nitrate) with hydrochloric acid; it forms tabular crystals, readily soluble in water, alcohol and ether.

Moseley, shortly after the discovery of the diffraction of X-rays by crystals, set to work to examine the X-ray spectrum of a number of elements each of which he made in turn the target of an X-ray tube.

Although bismuth is readily obtained in fine crystals by artificial means, yet natural crystals are rare and usually indistinct: they belong to the rhombohedral system and a cube-like rhombohedron with interfacial angles of 92° 20' is the predominating form.

There is a perfect cleavage perpendicular to the trigonal axis of the crystals: the fact that only two (opposite) corners of the cube-like crystals can be truncated by cleavage at once distinguishes them from true cubes.

Bismuth trifluoride, BiF3, a white powder, bismuth tribromide, BiBr 3, golden yellow crystals, bismuth iodide, Bi13, greyish-black crystals, are also known.

Nataloin, 2C17H1807�H20, forms bright yellow scales, melting at 212°-222°; barbaloin, C 17 H 18 0 7, forms yellow prismatic crystals.

Methods depending on the free suspension of the solid in a liquid of the same density have been especially studied by Retgers and Gossner in view of their applicability to density determinations of crystals.

When heated in a current of hydrogen it sublimes in the form of brilliant prismatic crystals.

By heating with sodium amalgam and separating with hydrochloric acid, the dichloride, TaC1 2.2H 2 O, is obtained as emerald green hexagonal crystals.

Derived products in the form of crystals of phillipsite are not uncommon, but the most abundant of all are the incrustations of manganese oxide, as to the origin of which Murray and Renard are not fully clear.

After long continued frost the last of the included brine may be frozen and the salts driven out in crystals on the surface; these crystals are known to polar explorers by the Siberian name of rassol.

The crystals are orthorhombic, with angles similar to those of marcasite; they are often prismatic in habit, and the prism M is usually terminated by the deeply striated faces of an obtuse dome r.

Mispickel occurs in metalliferous veins with ores of tin, copper, silver, &c. It is occasionally found as embedded crystals, for example, in serpentine at Reichenstein, Silesia.

This variety forms a passage to the species glaucodote, (Co,Fe)AsS, which is found as well-developed orthorhombic crystals in copper ore at Hakansboda in Ramberg parish, Vestmanland, Sweden.

Journ., 1828), he devoted himself chiefly to the examination of fluid-filled cavities in crystals, and of the microscopic structure of various kinds of fossil wood.

The crystals look like antimony, and are brittle, and so hard as to scratch glass and rubies; their specific gravity is 4.25.

The filtrate on cooling deposits crystals of potassium zirconofluoride, K 2 ZrF 6, which are purified by crystallization from hot water.

The orthorhombic form of the crystals, as distinct from the cubic form of pyrites, was recognized by Rome de 1'Isle in 1772, though later R.

Hairy considered the crystals to be only distorted cubic forms.

Usually they are twinned on a prism plane, M, producing pentagonal stellate groups of five crystals; twinning on the plain g, in which the crystals intercross at angles of nearly 60°, is less common.

Apart from crystalline form, the external characters of marcasite are very similar to those of pyrites, and when distinct crystals are not available the two species cannot always be easily distinguished.

About 15% of a volatile oil is obtained by distilling cubebs with water; after rectification with water, or on keeping, this deposits rhombic crystals of camphor of cubebs, C 15 H 26 O; cubebene, the liquid portion, has the formula C15HV4.

Subsequently he studied the expansion of solids by heat, and applied the phenomena of interference of light to the measurement of the dilatations of crystals.

Aqueous solutions deposit crystals containing 2, 4 or 6 molecules of water.

Hot or dilute cold solutions deposit minute orthorhombic crystals of aragonite, cold saturated or moderately strong solutions, hexagonal (rhombohedral) crystals of calcite.

Aragonite is the least stable form; crystals have been found altered to calcite.

Crystals may be obtained by heating di-calcium pyrophosphate, Ca2P207, with water under pressure.

The sulphydrate or hydrosulphide, Ca(SH)2, is obtained as colourless, prismatic crystals of the composition Ca(SH) 2.6H 2 O, by passing sulphuretted hydrogen into milk of lime.

Calcium metasilicate, CaSiO 3, occurs in nature as monoclinic crystals known as tabular spar or wollastonite; it may be prepared artificially from solutions of calcium chloride and sodium silicate.

Ammonia is found in small quantities as the carbonate in the atmosphere, being produced from the putrefaction of nitrogenous animal and vegetable matter; ammonium salts are also found in small quantities in rain-water, whilst ammonium chloride (sal-ammoniac) and ammonium sulphate are found in volcanic districts; and crystals of ammonium bicarbonate have been found in Patagonian guano.

It is easily liquefied and the liquid boils at-33-7° C., and solidifies at - 75° C. to a mass of white crystals.

It forms colourless crystals which are soluble in water and decompose on heating, with the formation of nitrogen.

Ammonium sulphide, (NH 4) 2 S, is obtained, in the form of micaceous crystals, by passing sulphuretted hydrogen mixed with a slight excess of ammonia through a well-cooled vessel; the hydrosulphide NH 4 �HS is formed at the same time.

It forms monosymmetric crystals which by boiling with water yield amidosulphonic acid.

With all the important work he accomplished in physics - the enunciation of Boyle's law, the discovery of the part taken by air in the propagation of sound, and investigations on the expansive force of freezing water, on specific gravities and refractive powers, on crystals, on electricity, on colour, on hydrostatics, &c. - chemistry was his peculiar and favourite study.

Several hydrates are known: 2NaOH 7H 2 O is obtained as large monoclinic crystals by' cooling a solution of specific gravity 1.365 to -8'; Pickering (Journ.

When dissolved in water it yields some NaOH and H202; on crystallizing a cold 'solution Na202.8H20 separates as large tabular hexagonal crystals, which on drying over sulphuric acid give Na 2 0 2.2H 2 0; the former is also obtained by precipitating a mixture of caustic soda and hydrogen peroxide solutions with alcohol.

Iooi), who obtained cubic crystals from a supersaturated solution of sodium and aluminium sulphates below 20°, higher temperatures giving monoclinic crystals.

Common washing soda or soda-crystals is the decahydrate, Na2C03 IoH 2 O, which appears as large clear monoclinic crystals.

quartz and felspar, which under ordinary conditions form more equidimensional crystals, would assume lenticular forms. In the necessary co-operation of these three causes, viz.

flattening of particles by compression, orientation of particles by flow and formation of laminar crystals, the fundamental explanation of slaty cleavage is found.

These crystals may be half an inch to several inches in length; they are usually more or less completely weathered to white mica and kaolin.

Further, unlike diamond, it never occurs as distinctly developed crystals, but only as imperfect six-sided plates and scales.

A deep red solution was obtained, but the free quinone was not isolated since the solution on standing deposits nearly black crystals of dihydroxyphenylhydroxybenzoquinone (HO)2C6H3 C6H202.OH.

The cadmium sulphate solution must be saturated and have free crystals of the salt in it.

For the zinc solution, take 55.5 parts by weight of crystals of zinc sulphate (ZnS0470H2) and dissolve in 44.5 p arts by weight of distilled water; the resulting FIG.

For the sulphate of copper solution, take 16.5 parts by weight of pure crystals of copper sulphate (CuSO 4 50H 2) and dissolve in 83.5 parts by weight of water; the resulting solution should have a specific gravity of 1.

These deposits, in addition to common salt, include the following minerals: sylvine, KC1; carnallite, KC1 MgC12.6H20 (transparent, deliquescent crystals, often red with diffused oxide of iron); kainite, K 2 SO 4 MgSO 4 MgC1 2 6H 2 O (hard crystalline masses, permanent in the air); kieserite MgS04 H20 (only very slowly dissolved by water); besides polyhalite, MgSO 4 K 2 SO 4.2CaSO 4.2H20anhydrite, CaSO 4; salt, NaC1, and some minor components.

It is a dark yellow powder, which fuses at a high temperature, the liquid on cooling depositing shining tabular crystals; at a white heat it loses oxygen and yields the monoxide.

Iodine dissolves in an aqueous solution of the salt to form a dark brown liquid, which on evaporation over sulphuric acid gives black acicular crystals of the tri-iodide, K1 3.

The filtrate is evaporated at a temperature not exceeding 60° or at most 70° C.; after sufficient concentration it deposits on cooling anhydrous crystals of the salt, while the potassium chloride, which may be present as an impurity, remains mostly in the motherliquor; the rest is easily removed by repeated recrystallization.

Potassium sulphide, K 2 S, was obtained by Berzelius in pale red crystals by passing hydrogen over potassium sulphate, and by Berthier as a flesh-coloured mass by heating the sulphate with carbon.

On saturating a solution of caustic potash with sulphuretted hydrogen and adding a second equivalent of alkali, a solution is obtained which on evaporation in a vacuum deposits crystals of K 2 S.5H 2 O.

It is readily soluble in water, and on evaporation in a vacuum over caustic lime it deposits colourless, rhombohedral crystals of 2KHS.H 2 0.

Potassium sulphite, K 2 S0 3, is prepared by saturating a potash solution with sulphur dioxide, adding a second equivalent of potash, and crystallizing in a vacuum, when the salt separates as small deliquescent, hexagonal crystals.

The very beautiful (anhydrous) crystals have the habit of a double six-sided pyramid, but really belong to the rhombic system.

Arecaidine forms white crystals easily soluble in water, and difficultly soluble in alcohol.

Guvacine, named from "guvaca," an Indian designation of the betel palm, forms white crystals.

Twinned crystals are not common, but the presence of polysynthetic twinning is sometimes shown by fine striations running diagonally or obliquely across the cleavage surfaces.

Galena is met with at all places where lead is mined; of localities which have yielded finely crystallized specimens the following may be selected for mention: Derbyshire, Alston in Cumberland, Laxey in the Isle of Man (where crystals measuring almost a foot across have been found), Neudorf in the Harz, Rossie in New York and Joplin in Missouri.

Good crystals have also been obtained as a furnace product.

Wood has studied the iridescent colours seen when a precipitate of potassium silicofluoride is produced by adding silicofluoric acid to a solution of potassium chloride, and found that they are due to the same cause, the refractive index of the minute crystals precipitated being about the same as that of the solution, which latter can be varied by dilution.

The free acid forms dark red deliquescent crystals and is obtained by decomposing the silver salt with hydrochloric acid, or the barium salt with dilute sulphuric acid.

It is obtained by hydrolysing cocaine with acids or alkalis, and crystallizes with one molecule of water, the crystals melting at 198° to 199° C. It is laevo-rotatory, and on warming with alkalis gives iso-ecgonine, which is dextro-rotatory.

They are composed of crystals of bile-fat, cholesterine.

Many of the crystals are parti-coloured, the blue being distributed in patches in a colourless or yellow stone; but by skilful cutting, the deep-coloured portion may be caused to impart colour to the entire gem.

They occur, with many other gem-stones, as pebbles or rolled crystals in alluvial deposits of sand and gravel; the gem-gravel being known locally as illam.

Madagascar yields sapphires generally of very deep colour, occurring as rolled crystals.

The rolled crystals of sapphire occur, with garnet and other minerals, in glacial deposits, and have probably been derived from dykes of igneous rocks, like andesite and lamprophyre.

The Helena crystals are of tabular habit, being composed of the basal pinacoid with a very short hexagonal prism, whilst at Yogo Gulch many of the crystals affect a rhombohedral habit.

Occasionally monoclinic crystals are obtained by crystallizing from a strong solution.

It contains, in addition to tannin, a peculiar principle called larixin, which may be obtained in a pure state by distillation from a concentrated infusion of the bark; it is a colourless substance in long crystals, with a bitter and astringent taste, and a faint acid reaction; hence some term it larixinic acid.

In the amorphous state it is a dull green, almost infusible powder, but as obtained from chromium oxychloride it is deposited in the form of dark green hexagonal crystals of specific gravity 5 2.

Chromium trioxide, Cr03, is obtained by adding concentrated sulphuric acid to a cold saturated solution of potassium bichromate, when it separates in long red needles; the mother liquor is drained off and the crystals are washed with concentrated nitric acid, the excess of which is removed by means of a current of dry air.

Chromous sulphate, CrS04 7H 2 0, isomorphous with ferrous sulphate, results on dissolving the metal in dilute sulphuric acid or, better, by dissolving chromous acetate in dilute sulphuric acid, when it separates in blue crystals on cooling the solution.

Chromic sulphate, Cr2(S04)3, is prepared by mixing the hydroxide with concentrated sulphuric acid and allowing the mixture to stand, a green solution is first formed which gradually changes to blue, and deposits violet-blue crystals, which are purified by dissolving in water and then precipitating with alcohol.

It forms brown crystals.

It occurs in small yellowish crystals, which are turned red by exposure to light or air.

The crystals are purified by recrystallization from water.

The four phases are (I) crystals of salt, (2) crystals of ice, (3) a saturated solution of the salt in water, and (4) the vapour, which is that practically of water alone, since the salt is non-volatile at the temperature in question.

At that temperature crystals of the anhydrous Na 2 SO 4 appear, and a new fixed equilibrium exists between the four phases - hydrate, anhydrous salt, solution and vapour.

When this process is complete the temperature rises, and we pass along a new curve giving the equilibrium between anhydrous crystals, solution and vapour.

In one case (represented by the point A in the figure) the solid which freezes out is a conglomerate of crystals of the compound with those of antimony, in the other case C with those of copper.

Still further evaporation causes these crystals to effloresce and pass into the anhydrous salt.

Crystals of ice may lie side by side with crystals of common salt, but each crystalline individual is either ice or salt; no one crystal contains both components in proportions which can be varied continuously.

But, in other cases, crystals are known in which both components may enter.

Such structures are known as mixed crystals or solid solutions.

Hence the conditions necessary to secure equilibrium when the solid phase is present are not the same as those necessary to cause crystallization to start in a number of crystals at first excessively minute in size.

If a solution of a salt be stirred as it cools in an open vessel, a thin shower of crystals appears at or about the saturation temperature.

These crystals grow steadily, but do not increase in number.

When the temperature has fallen about 10° C. below this point of saturation, a dense shower of new crystals appear suddenly.

From this and other evidence it has been shown that the first thin shower in open vessels is produced by the accidental presence of tiny crystals obtained from the dust of the air, while the second dense shower marks the point of spontaneous crystallization, where the decrease in total available energy caused by solidification becomes greater than the increase due to the large surface of contact between the liquid and the potentially existing multitudinous small crystals of the shower.

If the temperature at which this dense spontaneous shower of crystals is found be determined for different concentrations of solution, we can plot a "supersolubility curve," which is found generally to run roughly parallel to the "solubility curve" of steady equilibrium between liquid and already existing solid.

12) were inocu lated with crystals of A when its composition was that represented so by x, cooled very slowly and stirred, the conditions would be hose of equilibrium throughout.

6 When the temperature sank to a, on the freezing point curve, E40 crystals of pure A would appear.

The 20 40 60 80 100 liquid then becomes saturated with B also, and, if inoculated with B crystals, will deposit B alongside of A, till the whole mass is solid.

But, if no solid be present initially, or if the cooling be rapid, the liquid of composition x becomes supersaturated and may cool till the supersaturation curve is reached at b, and a cloud of A crystals comes down.

The conditions may then remain those of equilibrium along the curve f E, but before reaching f the solution may become supersaturated with B and deposit B crystals spontaneously.

of crystals of the solute, crystals will dissolve as solvent enters, and the solution remains saturated throughout.

Many deposits of limonite have been found, on being worked, to pass downwards into ferrous carbonate; and crystals of chalybite converted superficially into limonite are well known.

But it is obvious that certain distributions will predominate, for the crystals will tend to fall so as to offer the least resistance to their motion; a needle-shaped crystal tending to keep its axis vertical, a plate-shaped crystal to keep its axis horizontal.

Potassium aluminate, K 2 Al 2 0 4, is obtained in solution by dissolving aluminium hydrate in caustic potash; it is also obtained, as crystals containing three molecules of water, by fusing alumina with potash, exhausting with water, and crystallizing the solution in vacuo.

It forms colourless crystals, melting at 90°, and boiling at 265°-270°.

It forms colourless crystals, melting at 185°, and boiling at 360°.

On heating, the crystals lose water, swell up, and give the anhydrous sulphate, which, on further heating, gives alumina.

Aluminium nitride (A1N) is obtained as small yellow crystals when aluminium is strongly heated in nitrogen.

The nitrate, Al(N03)3, is obtained as deliquescent crystals (with 81120) by evaporating a solution of the hydroxide in nitric acid.

Chemie, 1886, 25, p. 118); it forms hexagonal crystals which melt at 1.6° C.

It forms small crystals, showing a brilliant green reflex, and is soluble in water and alcohol with formation of a deep red solution.

CH:C(CH 3) 2, forms yellow crystals which melt at 28° C. and boil at 197.2° C. When heated with phosphorus pentoxide it yields acetone, water and some pseudocumene.

Among those directly visible to the microscope are oil drops, often coloured (Uredineae) crystals of calcium oxalate (Phallus, Russula), proteid crystals (Mucor, Pilobolus, &c.) and resin (Polyporei).

The solid variety prepared by Staedel forms colourless, prismatic crystals which melt at -2° C.; it is decomposed with explosive violence by platinum sponge, and traces of manganese dioxide.

The majority of minerals are found commonly in masses which can with difficulty be recognized as aggregates of crystalline grains, and occur comparatively seldom as distinct crystals; but the diamond is almost always found in single crystals, which show no signs of previous attachment to any matrix; the stones were, until the discovery of the South African mines, almost entirely derived from sands or gravels, but owing to the hardness of the mineral it is rarely, if ever, water-worn, and the crystals are often very perfect.

o The crystals often display triangular markings, either elevations or pits, upon - ' g ?

the rounded crystals somewhat the appearance of drops of gum.

Diamond may break with a conchoidal fracture, but the crystals always cleave readily along planes parallel to the octahedron faces: of this property the diamond cutters avail themselves when reducing the stone to the most convenient form for cutting; a sawing process, has, however, now been introduced, which is preferable to that of cleavage.

Unlike other cubic crystals, diamond experiences a diminution of refractive index with increase of temperature.

Crystals belonging to the cubic system should not be birefringent unless strained; diamond often displays double refraction particularly in the neighbourhood of inclusions, both liquid and solid; this is probably due to strain, and the spontaneous explosion of diamonds has often been observed.

Bort (or Boart) is the name given to impure crystals or fragments useless for jewels; it is also applied to the rounded crystalline aggregates, which generally have a grey colour, a rough surface, often a radial structure, and are devoid of good cleavage.

The best glaziers' diamonds are chosen from crystals such that a natural curved edge can be used.

African mines the diamonds are not only crystals of various weights from fractions of a carat to 150 carats, but also occur as microscopic crystals disseminated through the blue ground.

The stones, however, are good; since they differ somewhat from the Kimberley crystals it is probable that they were not derived from the present pipes.

At Sao Joao da Chapada, in Minas Geraes, diamonds occur in a clay interstratified with the itacolumite, and are accompanied by sharp crystals of rutile and haematite in the neighbourhood of decomposed quartz veins which intersect the itacolumite.

The boulder is a crystalline rock consisting of pyroxene (chrome-diopside), garnet, and a little olivine, and is studded with diamond crystals; a portion of it is preserved in the British Museum (Natural History).

C: (NH) NH 2, forms colourless crystals which melt at 75-80° C. When warmed it breaks down into ammonia and cyanphenine (s-triphenyl triazine).

The felspathoid minerals, sodalite, haiiyne and nosean, which crystallize in isometric dodecahedra, are very frequent components of the phonolites; their crystals are often corroded or partly dissolved and their outlines may then be very irregular.

The conductivities of thin slices of crystals have been measured by C. H.

Crystals of blende belong to that subclass of the cubic system in which there are six planes of symmetry parallel to the faces of the rhombic dodecahedron and none parallel to the cubic faces; in other words, the crystals are cubic with inclined hemihedrism, and have no centre of symmetry.

Crystals exhibit pyroelectrical characters, since they possess four uniterminal triad axes of symmetry.

Crystals of blende are of very common occurrence, but owing to twinning and distortion and curvature of the faces, they are often rather complex and difficult to decipher.

A pure white blende from Franklin in New Jersey is known as cleiophane; snow-white crystals are also found at Nordmark in Vermland, Sweden.

Mention may be made of the brilliant black crystals from Alston Moor in Cumberland, St Agnes in Cornwall and Derbyshire.

Yellow crystals are found at Kapnik-Banya, near Nagy-Bánya in Hungary.

By evaporation of a solution of lanthanum oxide in hydrochloric acid to the consistency of a syrup, and allowing the solution to stand, large colourless crystals of a hydrated chloride of the composition 2LaC1 3.15H 2 O are obtained.

120-127) has obtained it in lustrous hexagonal crystals by electrolysing the double fluoride of beryllium and sodium or potassium with an excess of Crystal of beryl.

Beryllium oxide, beryllia or glucina, BeO, is a very hard white powder which can be melted and distilled in the electric furnace, when it condenses in the form of minute hexagonal crystals.

It is deliquescent, and readily soluble in water, from which it separates on concentration in crystals of composition BeC1 2.4H 2 0.

The sulphate is obtained by dissolving the oxide in sulphuric acid; if the solution be not acid, it separates in pyramidal crystals of composition BeSO 4.4H 2 0, while from an acid solution of this salt, crystals of composition BeS04.7H 2 O are obtained.

The crystals so obtained are very unstable and decompose rapidly with evolution of carbon dioxide.

By modern mineralogists the name chalcedony is restricted to those kinds of silica which occur not in distinct crystals like ordinary quartz, but in concretionary, mammillated or stalactitic forms, which break with a fine splintery fracture, and display a delicate fibrous structure.

Certain flat oval nodules from a decomposed lava (augite-andesite) in Uruguay present a cavity lined with quartz crystals and enclosing liquid (a weak saline solution), with a movable air-bubble, whence they are called "enhydros" or water-stones.

It occurs in all degrees of purity, from that of mere salty clay to that of the most transparent crystals.

All these names are derived from the size and appearance of the crystals, their uses and the modes of their production.

The boiled salts, the crystals of which are small, are formed in a medium constantly agitated by boiling.

The time varies for the unboiled salts from twelve hours to three or four weeks, the larger crystals being allowed a longer time to form, and the smaller ones being formed more quickly.

In Britain the brine is so pure that, keeping a small stream of it running into the pan to replace the losses by evaporation and the removal of the salt, it is only necessary occasionally (not often) to reject the mother-liquor when at last it becomes too impure with magnesium chloride; but in some works the mother-liquor not only contains more of this impurity but becomes quite brown from organic matter on concentration, and totally unfit for further service after yielding but two or three crops of salt crystals.

A slight degree of acidity seems more favourable to the crystallization of salt than alkalinity; thus it is a practice to add a certain amount of alum, 2 to 12 lb per pan of brine, especially when, as in fishery salt, fine crystals are required.

In most European countries a tax is laid on salt; and the coarser as well as the finer crystals are therefore often dried so as not to pay duty on more water than can be helped.

On extending his inquiry to other aelotropic crystals he observed a similar variation, and was thus led, in 1825, to the discovery that aelotropic crystals, when heated, expand unequally in the direction of dissimilar axes.

The excess held temporarily in solution is then deposited in crystals of CaS04.2H20.

The process goes on until a relatively small quantity of water has by instalments dissolved and hydrated the 2CaSO 4 H 2 O, and has deposited CaSO 4.2H 2 O in felted crystals forming a solid mass well cemented together.

There is reason to suppose that the change described takes place in two stages, the gypsum first forming orthorhombic crystals and then crystallizing in the monosymmetric system.

The yellow crystals melt at 190°, and when cooled down assume a red colour, which changes to the original yellow on standing.

Thallic chloride, T1C1 3, is obtained by treating the monochloride with chlorine under water; evaporation in a vacuum gives colourless deliquescent crystals of T1C1,.H20.

Thallic sulphate, T1 2 (SO 4) 3.7H 2 O, and thallic nitrate, Tl(NO 3) 3.8H 2 0, are obtained as colourless crystals on the evaporation of a solution of the oxide in the corresponding acid.