light, and is converted into cyanide of potassium. It unites with other bases and forms salts destitute of water. 100 c.i=55.99 grs. Cyanic Acid (Cy O, 4·25).- Obtained by heating yellow prussiate of potash with black oxide of manganese on an iron plate over a fire or lamp, until the whole becomes a black mass: by digesting the mass in water, and evaporating the solution, cyanate of potash is left in white scales (K O Cy O); monobasic acid.

Urea or Cyanate of Ammonia (C, O, N, H, 7·5). — If we take a solution of the preceding salt, mix it with sulphate of ammonia and evaporate, sulphate of potash crystallizes out first, and then 4 sided prisms of urea. It is also obtained from urine by evaporating that fluid down in a bason at the temperature of boiling water, and boiling the residue in spirit. The urea crystallizes out, and may be deprived of colour by means of animal charcoal. By uniting with 2 atoms of water, urea is rapidly changed into 2 atoms of carbonate of ammonia (C2 O2 N2 H, 2 HO becoming NH, CO, NH, CO2). It is the odour of the ammonia thus disengaged which is so perceptible in those parts of towns where this fluid is deposited. To preserve it from flying away, the urine should be mixed with sulphuric acid. For every 100 lbs. of cows' urine, 6 lbs. of sulphuric acid should be added to the tank containing it, and for horses' urine, a little more than 1 lb. for every 100 lbs. of fluid. Urea unites with acids and forms a series of salts. The nitrate may be formed by evaporating urine down to the consistence of a syrup and mixing it with an equal measure of nitric acid spec. grav. 1·42. The whole becomes a mass of scaly or needle crystals, consisting of one atom of urea, one of acid, and one of water.

Fulminic Acid (Cy2 O2 9.5). This is the active principle in fulminating mercury employed in percussion caps, and is prepared by mixing 1 part of mercury, 12 of nitric acid, (spec. grav. 1·36) and 11 of alcohol (spec. grav. 848), and heating in a flask in a water bath; the fulminate of mercury precipitates. It may be separated from the globules of mercury, by dissolving it in hot water, and crystallizing it out of the solution in fine silky needles. It explodes with great violence when the smallest quantity of it is rolled up in paper and struck with a hammer. It is, therefore, a dangerous substance to prepare, and none but chemists should attempt to make it. Fulminate of silver, prepared also in a similar manner, is an explosive compound. Percussion caps are filled by rubbing 10 parts of fulminate of mercury cautiously with a wooden pestle on a marble slab, with 30 parts of water; to this paste are added 6 parts of saltpetre, and the mixture introduced in proper proportion into the copper caps. Cyanic acid and fulminic acid present us with examples of isomerism, or bodies which have the same composition in 100 parts, but have totally different chemical characters. Cyanuric acid (Cy ̧ O ̧) is also isomeric.

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CYANOHYDRIC OR PRUSSIC ACID.

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Cyanohydric, Hydrocyanic, or Prussic Acid (HCy 3·375).—The method of preparing this acid is to distil in a retort 15 parts of pounded yellow prussiate of potash (ferrocyanide of potassium) with 9 parts of water and 9 parts of sulphuric acid. The distilled fluid is to be passed into a receiver surrounded with ice. But in this state it is too strong for safety. The hydrous acid is made by distilling 4 parts of prussiate, 18 of water, and 2 of oil of vitriol, into a receiver containing 20 parts of water. The process is carried on with the careful application of heat until the fluid in the receiver amounts to 38 parts.

Characters. It is a colourless acid, having a powerful odour similar to that of peach blossoms. Taste sharp, at first cooling, then burning. It scarcely reddens litmus paper. When very

strong it speedily decomposes, depositing a brown matter, which may be prevented by the addition of a drop or two of sulphuric acid, or of a small portion of alcohol. It forms, with nitrate of silver, a curdy precipitate, which disappears in nitric acid by boiling, and the smell of prussic acid is evolved. When freshly prepared a few drops of this acid speedily destroy animal life. It should not therefore be placed in the hands of inexperienced persons. Even during its preparation the fumes sometimes produce faintness. The best antidote in this case is to smell the vapour of strong caustic ammonia, which neutralizes the acid, and restores consciousness. The best tests for this acid are 1st, its smell; 2d, its action with nitrate of silver; 3d, when the fluid containing it is poured into a solution of a mixture of sulphates of peroxide and protoxide of iron (a decomposing specimen of copperas answers well), the fluid neutralized with ammonia, and then a few drops of chlorohydric acid added, a fine precipitate of Prussian blue falls down, which is characteristic. But the most beautiful test is the following (Liebig). 4. Pour into a test tube half a drachm of the suspected fluid, an equal bulk of sulphohydret of ammonia, and 4 grains of flowers of sulphur. Boil over a lamp until the smell of SH disappears. Filter, and add a drop of the liquid to a solution of pernitrate or perchloride of iron. A blood red sulphocyanide of iron falls. Cyanide of Potassium (KCy 8.25). A salt crystallizing in white cubes; may be prepared by calcining the yellow prussiate of potash in a close vessel, digesting the residue in cold water, filtering, evaporating to dryness, and boiling the white residue with alcohol, Sp. grav. 896. The cyanide separates on cooling. It is sometimes used for photographic purposes, and then its purity is of less consequence. When 8 parts of dried yellow prussiate are fused in a covered clay crucible, with 3 parts of dry carbonate of potash, the mixture becomes black, the portion on the surface being a clear fluid. It is to be poured off from the

dark matter at the bottom into a porcelain bason or upon a clean slab. It contains some cyanate and carbonate of potash.

Ferrocyanide of Potassium (Cy Fe, K4, or Cy, Fe K2). Iron Cyanide of Potash, or Yellow Prussiate of Potash.-This salt crystallizes in truncated octahedrons, and is made by heating carbonate of potash in an iron pot, and stirring into the fused mass animal matters, such as hoofs, horns, woollen rags, or any substances containing nitrogen. The salt is then removed from the pot, and digested in water. This liquor when evaporated yields the yellow prussiate in large beautiful yellow crystals. It can also be formed by passing the nitrogen of the air over potash and charcoal intensely heated. It is soluble in water, and affords the best test for peroxide of iron, and oxide of copper, which we possess. If we add a drop of it to a weak solution of perchloride of iron, Prussian blue immediately falls, and when mixed in a similar manner with a solution of copper, a brownish red precipitate makes its appearance.

Prussian Blue (Fe 7 Cy,) is the fine blue colour used for dyeing woollen dresses, and is made as above described. It pos sesses a fine soft dark blue colour, and is often used under the name of blue by washerwomen to hide the yellow colour of linen. Blue ink is prepared by triturating Paris Prussian blue with of its weight of oxalic acid in water. Ferridcyanide of potassium, or Red Prussiate of Potash, Cy Fe, K,, is a fine red prismatic salt, and is obtained by exposing the yellow prussiate in powder to the action of an atmosphere of chlorine. This gas removes one atom of potassium, and forms chloride of potassium (Cy。 Fe, K and Cl becoming Cy, Fe, K, and K CI). This is the best test which we possess for the protoxide of iron, thus forming a fine Prussian blue, having the composition above described. The manufacture of the preceding substances is one of great importance in the arts, as from them proceed some of the finest colours in the whole range of chemistry. It is believed that by heating animal matter and potash together, a cyanide of potassium is formed (K Cy), while iron is removed from the pots, and when the contents of the pots are digested in water the cyanide dissolves up the iron, and forms the yellow prussiate. Similar compounds are formed by means of cobalt and cyanogen. The iron is believed to unite with the cyanogen, in the form of what is termed an organic radical (Cy, Fe), and this again with potassium. In the red prussiate this radical is supposed to be doubled (Cy Fe,).

Sulphocyanide of Potassium (K Cy S2) is obtained by heating 1 part of flowers of sulphur with 2 parts of powdered yellow prussiate previously dried at 212°. Dissolve the fused mass in water, and add a solution of carbonate of potash as long as a precipitate of iron falls; boil the mixture, filter and evaporate. Long prisms and needles separate, which are poisonous. This salt

COMPOUNDS FROM URIC ACID.

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affords a beautiful test for peroxide of iron. A quantity of iron present in a dilute solution is made apparent on the addition of a few drops of a solution of this salt in the form of a fine blood red colour.

Platinocyanide of Potassium (Pt Cy, K), in fine bluish yellow needles, is formed by fusing in a porcelain bason over a lamp 2 parts of dry yellow prussiate with 1 part of spongy platinum, dissolving the fused mass in water, filtering and crystallizing. If Cl be passed through a solution of this salt, a brilliant golden salt is formed, containing half the amount of potassium. Palladium, iridium, chromium, and manganese form similar salt radicals.

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Cyanogen unites with chlorine in two proportions, forming a gaseous and solid chloride; it also unites with barium. Mellon, C6 N4, yellow powder, an organic base obtained by heating in a retort, to redness sulphocyanogen; it decomposes into CS2, sulphur and mellon; with potassium forms mellonide of K, from which hydromellonic acid may be obtained by HCl. When mellon is boiled with NO, octahedral crystals appear of cyanilic acid, having the same composition as cyanuric acid. Melam, C12 N11 H9, white powder, obtained by heating sulphocyanide of ammonium to the point of fusion; the products are NH3, SH, CS2, and melam. Melamine, C6 N6 H6, yellow rhombic octahedrons, obtained by boiling crude melam, after removing KCl, with weak caustic potash. Ammeline, C6 N5 H5 O2, silky needles insoluble in alcohol and ether, obtained from the caustic solution after the preparation of the preceding body; it exists in the liquid, and is precipitated by acetic acid. This is treated with NO5, converted into nitrate of ammeline, 4-sided square prisms, and is precipitated pure by carbonate of ammonia. Ammelide, C12 Ng H, 06, white powder, insoluble in water, alcohol, and ether, but soluble in acids and alkalies obtained by treating melam, melamine, or ammeline, by solution in SO3, mixing with alcohol, and washing the precipitate with water. Sulphomellone, C6NH3 S4? Hydrosulphomellonic acid, obtained by treating sulphocyanogen with KS, HS, and adding acetic acid. Uric acid, C10 N4 H4 O6, or 2Cy+4CO (Urile)+Urea, brilliant scales and needles; contained abundantly in the urine of fowls and boa constrictors, and frequently in guano, if not too much decomposed. The acid may be obtained by boiling the dung of the boa with a dilute solution of caustic potash till NH, ceases to be expelled and filtering. On the addition of HCl to the filtered liquor uric acid precipitates, and is to be well washed. It unites with bases forming with soda, urate of soda: often found in the joints of gouty persons, and known as chalk stones. Uric acid is the most common constituent of calculi; it may be distinguished by its dissolving in NO5, and giving a purple colour when carefully evaporated in a white basin, or by adding fuming acid, and then NH3. Allantoin, C4 H3 N2 O3, colourless rhombic prisms, obtained by boiling 1 uric acid, 20 water; brown oxide of lead is to be added as long as its colour changes. The allantoin is obtained by filtration and evaporation; this substance occurs in the allantoic fluid of the cow. Alloxan, Cg N2 H4O10, colourless right prisms, efflo rescent, obtained by dissolving uric acid in NO5 (145), and allowing the mother liquid to drain off. Alloranic acid, Cg N2 H2 Og 2HO, radiated needles, obtained by treating alloxan with alkalies. Leucoturic acid, C6 N2 H3 06, white powder, obtained by evaporating a strong solution of alloxanic acid at a certain temperature. Difluan is found in the liquid which deposites the preceding acid. Mesoxalic acid, formed by heating alloxanate of barytes to the boiling point. Mycomelinic acid, prepared by heating alloxan with an excess of ammonia. Parabanic acid, formed by heating alloxan or uric acid with NO5, and evaporating. Oxaluric acid, obtained by heating parabanic acid with NH3; the acid may be separated by SO3. Thionuric acid, formed by causing sulphite of NH3 to act on alloxan. Üramile is prepared by treating thionurate of NH3 with HCI. Uramil c acid, prepared from the preceding by treating with SO3. Alloxantine, Cg N2 H5 O10, oblique 4-sided prisms, formed by adding dilute NO, to uric acid, and evaporating down one third; or by

passing SH through alloxan. Dialuric acid, obtained by passing SH through a boiling solution of alloxantine and adding NH3; dialurate of NH3 separates in silky crystals. Allituric acid, prepared by boiling alloxantin with HCINO5. Dilituric acid, obtained from the mother liquor of the preceding body by SH. Murexide, C12 N5 H6 Og, purpurate of NH3 of Prout, 4-sided prisms, with a beautiful green metallic lustre, obtained by dissolving uric acid in dilute NO5, and evaporating till it acquires a flesh colour; it is treated with NH3 in slight excess; it is then diluted with half its weight of boiling water, and allowed to cool. It may also be obtained by mixing 7 grs. alloxan, 5 alloxantine, dissolved in 240 grs. water, with 80 grs. of a cold strong solution of carbonate of ammonia. Murexan, C6 N2 H4 05, purpuric acid of Prout, silky scales, insoluble in water; prepared by dissolving murexide in caustic potash, and adding SO3 in excess. Xanthic oxide, C5 N2 H2O2, a rare calculus, dissolves in NO5, leav ing a yellow residue, which is not redissolved by NH3; somewhat soluble in water. Cystic oxide, an organic base, C6 NH604 S2, yellowish white crystals; a rare calculus, soluble in alkalies, decomposed by heat, with evolution of SÓ2, and NH3. Guanine, C10 H5 N5 O2, white crystalline powder, extracted from guano by HCl, and precipitated by alkalies; it is a base uniting with acids and forming salts. Hyperuric acid (C10 N4 H3O7 2 H C) by oxidating guanine.

BORON.

B, 1.25, a brown powder obtained by heating, in a tube, calcined boracic acid with potassium (BO, and 3K become B and 3KO); the oxygen is removed by the potassium and forms caustic potash, while the boron is set free; the potash may be washed out with water, and the boron remains. Boracic acid, BO3, 4.25, white 6-sided pearly scales, which are obtained in an impure state in the hot springs of Tuscany. It may be purified by uniting it with soda, and decomposing the borax thus formed by sulphuric acid. It dissolves in sulphuric acid, water, and alcohol. Its presence can be easily distinguished when it is in solution in alcohol. If we place the solution in a bason, and set fire to it, the edges of the flame are tinged with a green colour. Test in combination. - Pour on it SO3, add alcohol, and burn it; if this acid is present the flame will be tinged green. Borax, NaO 2BO3 10HO 23.75. This salt may be prepared as already described. It occurs also native in Thibet, under the name of tincal. It crystallizes in 6-sided prisms, and con verts vegetable blues to green; a curious anomaly in the history of an acid salt. This salt is employed in certain diseases of the mouth in children, and is then given mixed with honey. It is used also as a flux for metals, and for detecting substances before the blowpipe (p. 17.). It enters as a constituent into the glazes employed for the finer kinds of porcelain.

SILICON. Si. 1.

This substance is the basis of flint, quartz, sand, &c., is a brown powder resembling boron,and may be procured by an analogous process.

Silica or Silicic Acid (Si O 2). This is one of the most common constituents of the globe, and is well known under various names. 1. Quartz, when pure, is milk-white, and is then known under the title of chucky stones; when violet coloured it is called amethyst; when red, rose quartz; cairngorum when yellowish; when crystallized and transparent in 6 sided prisms terminated by 6 sided pyramids, it is called rock crystal. Brazil, these crystals occur of such large size, that the eyes of spectacles are usually made from them; their advantage over glass

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