with much manual labour and dexterity. When the conversion into a chemical compound is seen to be completed by the cessation of the fetid animal vapours, remove the pasty mass with an iron ladle. If this be thrown, while hot, into water, some of the prussic acid will be converted into ammonia, and of course the usual product diminished. Allow it to cool, dissolve it in water, clarify the solution by filtration or subsidence, evaporate, and, on cooling, yellow crystals of the ferroprussiate of potash will form. Separate these, redissolve them in hot water, and by allowing the solution to cool very slowly, larger and very regular crystals may be had. This salt is now manufactured in several parts of Great Britain, on the large scale; and therefore the experimental chemist need not incur the trouble and nuisance of its preparation. Nothing can exceed in beauty, purity, and perfection, the crystals of it prepared at Campsie, by Messrs Mackintosh and Wilson. An extemporaneous ferroprussiate of potash may at any time be made, by acting on prussian blue, with pure carbonate of potash, prepared from the ignited bicarpreviously digested, at a moderate heat, for an hour or two in its own weight of or bitartrate. The blue should be sulphuric acid diluted with five times its weight of water; then filtered, and thoroughly edulcorated by hot water, from the sulphuric acid. Of this purified prussian blue, add successive portions to the alkaline solution, as long as its colour is destroyed, or while it continues to change from blue to brown. Filter the liquid, saturate the slight alkaline excess with acetic acid, concentrate by evaporation, and allow it slowly to cool. Quadrangular bevelled crystals of the ferroprussiate of potash will form. This salt is transparent, and of a beautiful lemon or topaz yellow. Its specific gravity is 1.830. It has a saline, cooling, but not unpleasant taste. In large crystals it possesses a certain kind of toughness, and, in thin scales, of elasticity. The inclination of the bevelled side to the plane of the crystal is about 135°. It loses about 13 per cent of water, when moderately heated; and then appears of a white colour, as happens to the green copperas: but it does not melt like this salt. The crystals retain their figure till the heat verges on ignition. At a red heat it blackens, but, from the mode of its formation, we see that even that temperature is compatible with the existence of the acid, provided it be not too long continued. Water at 60° dissolves nearly onethird of its weight of the crystals; and at the boiling point, almost its own weight. It is not soluble in alcohol; and hence, chemical compilers, with needless scrupulosity have assigned to that liquid the hereditary sinecure of screening the salt from the imaginary danger of atmospherical action. It is not altered by the air. Exposed in a retort to a strong red heat, it yields prussic acid, ammonia, carbonic acid, and a coaly residue consisting of charcoal, metallic iron, and potash. When dilute sulphuric or muriatic acid is boiled on it, prussic acid is evolved, and a very abundant white precipitate of protoprussiate of iron and potash falls, which afterwards, treated with liquid chlorine, yields a prussian blue, equivalent to fully one-third of the salt employed. Neither sulphuretted hydrogen, the hydrosulphurets, nor infusion of galls, produce any change on this salt. Red oxide of mercury acts powerfully on its solution at a moderate heat. Prussiate of mercury is formed, which remains in solution; while peroxide of iron and metallic mercury precipitate. Thus we see that a portion of the mercurial oxide is reduced, to carry the iron to the maximum of oxidizement. The solution of ferroprussiate of potash is not affected by alkalis; but it is decomposed by almost all the salts of the permanent metals. The following table presents a view of the colours of the metallic precipitates thus obtained. Solutions of Give a Protoxide of copper, White. Deutoxide of copper, Crimson brown. Deutoxide of mercury, White. If some of these precipitates, for example those of manganese or copper, be digested in a solution of potash, we obtain a ferroprussiate of potash and iron exactly similar to what is formed by the action of the alkaline solution on prussian blue. Those precipitates, therefore, contain a quantity of iron. I think this fact is very favourable to the theory of Mr. Porrett; and scarcely explicable on any other supposition. This salt is composed of the following constituents, by the latest analyses. Mr. Porrett. Dr. Thomson. Potash, Ferrochyazic acid, 44.53 Water, 40.34 15.13 100.00 41.64 45.90 13.00 100.54 We have seen the enormous discrepan cies with regard to the estimates of the ultimate acid constituents by these two experimentalists; and if we consider the directness and simplicity of the methods by which the primary constituents of the salt may be ascertained, the above differences also seem too great. By a well regulated desiccation, the water of crystallization may be pretty nearly determined; and the concurring results of experiment give for its quantity 13 per cent. Now the action of nitric acid properly conjoined with that of heat, should decompose and dissipate the gaseous part of the acid, and convert the iron into an insoluble peroxide; the weight of potash may then be exactly determined, first by saturation with acid, and secondly, by the weight of resulting salt. In fact had Mr. Porrett adhered to his experimental numbers, and not modified them by his atomical notions, we should have had the following results, which are probably correct. Potash, Water, 41.68 13.00 Ferrochyazic acid, 45.32 100.00 And from this real analysis, we deduce directly from the proportion of potash = 41.68, the apparent prime equivalent of White, passing to this neutral salt to be = 14.29; or rather Nickel, Apple green. Lead, White. Silver, and Gold, None, 3.375 12.00 28.275 100.00 We have treated the subject of the ferroprussiate of potash at considerable detail, since it is one of the most valuable re-agents, which the chemist possesses, in metallic analysis. Ferroprussiate of soda may be prepared from prussian blue, and pure soda, by a similar process to that prescribed for the preceding salt. It crystallizes in four-sided prisms, terminated by dihedral sum mits. They are yellow, transparent, have a bitter taste, and effloresce, losing in a warm atmosphere 37 per cent. At 55° they are soluble in 4 parts of water, and in a much less quantity of boiling water. As the solution cools, crystals separate. Their specific gravity is 1.458. They are said by Dr. John to be soluble in alcohol. Ferroprussiate of lime may be easily formed from prussian blue and lime-water. Its solution yields crystalline grains by evaporation. Ferroprussiate of barytes may be formed in the same way as the preceding species; or much more elegantly by Mr. Porrett's process, described already in treating of the ferroprussic acid. Its crystals are rhomboidal prisms, of a yellow colour, and soluble in 2000 parts of cold water, and 100 of boiling water. By Mr. Porrett's second account of this salt, it is composed 84.84 of 41.49 1 atom 97.00 204.48 These results were given in the Annals of Philosophy for September 1818. In Dr. Thomson's System, published in October 1817, we have the following statement :"Mr. Porrett has analyzed this salt with much precision. According to his experiments, it is composed of substance so unalterable and so easily ascertained as barytes; for Dr. Thomson's quotation gives of this substance 49.1 per cent.; the second account makes it 47.5; and the last 52.22. The quantity of bary. tes may be determined absolutely, without being deduced from, or entangled with, the estimate of water or acid. Ferroprussiate of strontian and magnesia have also been made. Ferroprussiate of iron. With the protoxide of iron and this acid we have a white powder, which, on exposure to air, becomes blue, passing into deutoferroprussiate of iron, or prussian blue. We have already described the method of making the ferroprussiate of potash, which is the first step in the manufacture of this beautiful pigment. This is usually made by mixing together one part of the ferroprussiate of potash, one part of copperas, and four parts or more of alum, each previously dissolved in water. Prussian blue, consisting of the deutoferroprussiate of iron, mixed with more or less alumina, precipitates. It is afterwards dried on chalk stones, in a stove. Pure prussian blue is a mass of an extremely deep blue colour, insipid, inodorous, and considerably denser than water. Neither water nor alcohol has any action on it. Boiling solutions of potash, soda, lime, barytes, and strontites decompose it; forming on one hand soluble ferroprussiates with these bases, and on the other a residue of brown deutoxide of iron, and a yellowish brown subferroprussiate of iron. This last, by means of sulphuric, nitric, or muriatic acid, is brought back to the state of a ferroprussiate, by abstracting the excess of iron oxide. Aqueous chlorine changes the blue to a green in a few minutes, if the blue be recently precipitated. Aqueous sulphuretted hydrogen, reduces the blue ferroprussiate to the white protoferroprussiate. Its igneous decomposition in a retort has lately been executed by M. Vauquelin with minute attention. He regards it as a hydrocyanate or mere prussiate of iron; but the changes he describes are very complex, nor do they invalidate Mr. Porrett's opinion, that it is a combination of red oxide of iron, with a ferruretted acid. The general results of M. Vauquelin's analysis, were hydrocyanic acid, hydrocyanate of ammonia, an oil soluble in potash, crystalline needles, which contained no hydrocyanic acid, but were merely carbonate of ammonia; and finally, a ferreous residue slightly attracted by the magnet, and con12.12 taining a little undecomposed prussian blue. If we are to regard prussian blue as a deutoferroprussiate of iron, then by Mr. Porrett's latest considerations, it would Porrett gives as its true proportions, 1 atom ferrochyazic acid, 66.25 35.66 1 atom barytes, 97. 2 atoms water, 22.5 In the Annals for October 1819, Mr. 52.22 185.75 100.00 The discrepancies are singular, with a be composed of persulphate of copper, and protosulphate of iron, in the proportion of two of the former salt to three of the latter, until the Dr. Thomson, after reporting it from Mr. crimson colour disappears. Sulphuro Porrett to consist of prussiate of copper falls. Boil this with a solution of potash, which will separate the copper. 'Distil the liquid mixed with sulphuric acid in a glass retort, and the peculiar acid will come over. By saturation with carbonate of barytes, and then throw 6.75 5.00 of sulphuric acid, the sulphuroprussic acid is obtained pure. thinks it likely that the true composition is, ing down this by the equivalent quantity Ferrocyanic acid, Peroxide of iron, Proust, in the Annales de Chimie, vol. Ix. states, that 100 parts of prussian blue, without alum, yield 0.55 of red oxide of iron by combustion; and by nitric acid, 0.54. 100 of prussiate of potash and iron, he further says, afford, after digestion with sulphuric or nitric acid, 35 parts of prussian blue. If we compare with this, Mr. Porrett's earliest estimate of 34.23 per cent of ferreous peroxide, besides the third of the weight of the acid, = 17.79, which being metallic iron, is equivalent to 25.4 of peroxide, we shall have the sum 59.63, as the quantity of peroxide in 100 of prussian blue, calling the atom of iron 3.5, and of peroxide 5.0. Or if we take Dr. Thomson's correction, we have the following numbers, supposing it to consist of 1 atom acid, 6.75 4.8.2 2 * SULPHUROPRUSSIC ACID; the sulphuretted chyazic acid of Mr. Porrett. Dissolve in water one part of sulphuret of potash, and boil it for a considerable time with three or four parts of powdered prussian blue added at intervals. Sulphuret of iron is formed, and a colourless liquid containing the new acid combined with potash, mixed with hyposulphite and sulphate of potash. Render this liquid sensibly sour, by the addition of sulphuric acid. Continue the boiling for a little, and when it cools, add a little peroxide of manganese in fine powder, which will give [18] VOL. Is It is a transparent and colourless liquid, possessing a strong odour, somewhat resembling acetic acid. Its specific gravity is only 1.022. It dissolves a little sulphur at a boiling heat. It then blackens nitrate of silver; but the pure acid throws down the silver white. By repeated distillations, sulphur is separated and the acid is decomposed. Mr. Porrett, in the Annals of Phil. for May 1819, states the composition of this acid, as it exists in the sulphuretted chyazate of copper, to be 2 atoms sulphur, carbon, 2 4,000 1.508 -1.754 hydrogen, - 0.132 7.394 This is evidently an atom of the hydros cyanic acid of M. Gay-Lussac, combined with 2 of sulphur. If to the above we add 9. for an atom of protoxide of copper, we have 16.394 for the prime equivalent of the metallic salt. When cyanogen and sulphuretted hydrogen were mixed together by M. Gay Lussac in his researches on the prussic principle, he found them to condense into yellow acicular crystals. Mr. Porrett has since remarked, that these crystals are not formed when the two gases are quite dry, but that they are quickly produced if a drop of water is passed up into the mixture. He does not think their solution in water corresponds to liquid sulphuretted chyazic acid; it does not change the colour of litmus; it has no effect on solutions of iron; it contains neither prussic nor sulphuretted chyazic acid, yet this acid is formed in it when it is mixed first with an alkali and then with an acid. The same treatment does not form any prussic acid. The facility with which the atomic hypothesis may be twisted to any theoretical perversion, rversion, is well exemplified in the following passage: ---"The weight of an atom of hydrocyanic acid is 3.375, and that of an atom of sulphur 2. But 6.328" (Mr. Porrett's first proportion of sulphur) "not being a multiple of two, this statement does not accord well with the atomic ther ry. It agrees much better with that theory, if we suppose the acid to be a compound of sulphur and cyanogen. Its con stitution will then be, Sulphur, Cyanogen, Thus we see that it is a compound of 1 atom of cyanogen and 3 atoms of sulphur." Thomson's System, Vol. ii. p. 292. This procedure looks more like legerdemain than philosophical research. Had Dr. Thomson contented himself with say ing that the statement of Mr. Porrett did not accord with the atomic theory, he would have said right; and there he should have left the matter, or have instituted experiments to settle the point. But to create a new genus of compounds, sulphur and cyanogen, and erect it into a new acid, on such a frivolous conceit, throws an air of ridicule on the science. Nay further, the Doctor describing M. Gay-Lussac's crystalline compound of sulphuretted hydrogen and cyanogen, says, that " as far as its description goes, this substance agrees exactly with the sulphuretted chyazic acid of Mr. Porrett. If we abstract the hydrogen of the sulphuretted hydrogen, which probably did not enter into the composition of the compound, it will be a compound of 1 atom cyanogen, and 14 atom sulphur, or in whole numbers of 2 atoms cyanogen and 3 atoms sulphur. So that it will contain just half the quantity of sulphur which Mr. Porrett found." M. GayLussac expressly states that the yellow needles obtained from the joint action of cyanogen and sulphuretted hydrogen, are "composed of one volume of cyanogen, and 11⁄2 volume of sulphuretted hydrogen." So that instead of containing no hydrogen, this substance contains half a volume more than hydrocyanic acid. The sulphuroprussiates have been examined only by Mr. Porrett. That of the red oxide of iron is a deliquescent salt, of a beautiful crimson colour. It may be obtained in a solid form by an atmosphere artificially dried. A concise account of these sans is given in the 5th Vol. of the Annals of Philos.* * ACID (PURPURIC). The excrements of the serpent Boa Constrictor, consist of pure lithic acid. Dr. Prout found that on digesting this substance thus obtained, or from urinary calculi, in dilute nitric acid, an effervescence takes place, and the lithic acid is dissolved, forming a beautiful purple liquid. The excess of nitric acid being neutralized with ammonia, and the whole concentrated by slow evaporation, the colour of the solution becomes of a deeper purple, and dark red granular crystals, sometimes of a greenish hue externally, soon begin to separate in abundance. These crystals are a compound of ammo nia with the acid principle in question. The ammonia was displaced by digesting the salt in a solution of caustic potash, till the red colour entirely disappeared. This alkaline solution was then gradually dropped into dilute sulphuric acid, which, uniting with the potash, left the acid principle in a state of purity. This acid principle is likewise produced. from lithic acid by chlorine, and also, but with more difficulty, by iodine. Dr. Prout, the discoverer of this new acid has, at the suggestion of Dr. Wollaston, called it purpuric acid, because its saline compounds have for the most part a red or purple colour.. This acid, as obtained by the preceding process, usually exists in the form of a very fine powder, of a slightly yellowish or cream colour; and when examined with a magnifier, especially under water, appears to possess a pearly lustre. It has no smell, nor taste. Its spec. grav. is considerably above water. It is scarcely soluble in water. One-tenth of a grain, grain, boiled for a con-siderable time in 1000 grains of water, was not entirely dissolved. The water, however, assumed a purple tint, probably, Dr. Prout thinks, from the formation of a little purpurate of ammonia. Purpuric acid is insoluble in alcohol and ether. The mineral acids dissolve it only when they are concentrated. It does not affect litmus paper. By igniting it in contact with oxide of copper, he determined its composition to be, 2 atoms hydrogen, 0.250 2 carbon, 2 4.54 1.500 27.27 Purpuric acid combines with the alkalis, alkaline earths, and metallic oxides. It is capable of expelling carbonic acid from the alkaline carbonates by the assistance of heat, and does not combine with any other acid. These are circumstances sufficient, as Dr. Wollaston observed, to distinguish it from an oxide, and to establish its character as an acid. Purpurate of ammonia crystallizes in quadrangular prisms, of a deep garnet-red colour. It is soluble in 1500 parts of water at 60°, and in much less at the boiling temperature. The solution is of a beautiful deep carmine, or rose-red colour. It has a sl a slightly sweetish taste, but no smell. Purpurate of potash is much more soluble; of soda is less; that of lime is nearly insoluble; those of strontian and lime are slightly soluble. All the solutions have the characteristic colour. Purpurate of magnesia is very soluble; and in solution, of a very beautiful colour. A solution of acetate of zinc produces with purpurate |