chemical purposes. Its specific gravity is in general not so high as our London platinum, though I once had a crucible made in Paris above 21 in specific gravity. M. Leithner, who has the charge of the porcelain manufactory at Vienna, has lately proposed a new method of rendering platinum malleable. It is exceedingly simple, and appears to answer well enough in a small scale, though it is not adapted for the construction of large vessels. It consists in making up the fine powder of pure platinum into a paste with oil of turpentine, and laying it in coats upon paper, allowing one coat to dry before another is applied, and continuing to add coats till the layer of platinum is of sufficient thickness. When this is done upon porcelain, and the vessel afterwards exposed to the temperature of from 14° to 18° Wedgwood, the platinum adheres, and may be burnished. When laid upon paper, and then exposed to a strong heat gradually raised, a sheet of platinum remains, which may be hammered, and converted into any shape that is wanted.

7. Palladium and Rhodium.-Vauquelin's method of separating these metals from crude platina, and obtaining them in a state of purity, has been given so lately in the Annals of Philosophy, that I do not think it necessary to repeat it here. It is sufficiently complicated; and, as far at least as palladium is concerned, does not seem nearly so easy as the method previously given by Dr. Wollaston by means of prussiate of mercury, though it is possible that Vauquelin's process may yield a greater quantity.

8. Gilding on Steel.-Gehlen has tried the following method of gilding on steel, and found it to answer. The steel is to be in the first place polished; the part to be gilt is to be rendered rough by means of nitric acid; the steel is then to be dipped into the solution containing the gold; the gold adheres to the rough part of the steel, and may be burnished.

9. Phosphuret of Copper.-If we believe Dobereiner, phosphuret of copper, prepared by Sage's method, contains not only copper and phosphorus, but likewise calcium. To this last metal, in his opinion, the analogy of the phosphuret to steel is owing.

10. Separation of Gold and Silver.-Professor Schnaubert, of Moscow, has lately made several attempts to separate silver from gold by boiling the alloy in sulphuric acid; this acid dissolves the silver, and leaves the gold. The process, though by no means brought to a state of perfection, promises at present to be attended with success. The great difference between the price of sulphuric acid and nitric acid, which is usually employed for the purpose, renders it desirable that this process, which I conceive originated with Mr. Keir, should be subjected to farther trials.

11. Zinc.-From my analysis of blende, published in the Annals of Philosophy, iv. 89, we may conclude that oxide of zinc is com posed of 100 metal + 24:42 oxygen; and sulphuret of zinc of 100 metal +48.81 sulphur; and an atom of zinc weighs 4:095.

12. Antimony.-From my analysis of sulphuret of antimony, (Ibid. p. 95,) it follows that it is composed of 100 metal + 35·556

sulphur. If we suppose it a compound of one atom metal + two atoms sulphur, then an atom of antimony will weigh 11-249.

V. Re-agents.

I shall state under this head the result of some experiments undertaken by different persons to determine the best re-agents for detecting the presence of different bodies in solution.

1. Mercury.-Professor Pfaff, of Kiel, has made a set of experiments on the best means of detecting mercury in solution, especially when in the state of corrosive sublimate. The following are the general conclusions which he considers himself as warranted to draw from these experiments :

The experiments hitherto made on the action of sulphureted hydrogen on solutions of mercury, are in contradiction with each other, and of course insufficient to answer the purpose for which they were intended.

Water impregnated with sulphureted hydrogen is the most delicate test of the presence of corrosive sublimate and pernitrate of mercury; for it discovers these salts, though diluted with 40,000 times their bulk of water, and though they do not exceed the quantity of or part of a grain.

The action of this liquid upon solutions of mercury is distinguished from its action on all other metals by this circumstance-if there be present in the solution any peroxide of mercury, the precipitate, which is at first in brownish or blackish flocks, becomes very speedily white. The addition of the smallest quantity of peroxide of mercury will render the black precipitate white, provided it be agitated.

Protoxide of mercury in all cases produces a black precipitate with sulphureted hydrogen.

If a small piece of copper coin be put into the solution suspected to contain mercury, it will be covered with a white coating, or at least with white streaks; which, when rubbed, acquire the metallic lustre. By this method Mr. Pfaff was able to detect the presence of of a grain of corrosive sublimate when dissolved in 20,000 times its weight of water.

2. Muriatic Acid.-Mr. Meyer, of Stettin, has made some curious observations on the delicacy of nitrate of silver, pronitrate of mercury, pernitrate of mercury, and the solution of subpernitrate of mercury in water, as tests for the discovery of muriatic acid. He found nitrate of silver the most delicate of these four salts. It detected one part of muriatic acid dissolved (in the state of common salt) in 113,664,000 parts of water; but upon this very dilute solution the other three salts had no effect. A solution of one part acid in 56,832,000 parts of water was not affected by the mercurial salts. A solution of one part muriatic acid in 28,416,000 parts of water was rendered slightly opalescent by the pronitrate of mercury, but not altered by the two other mercurial salts. A solution of one part of muriatic acid in 14,208,000 parts of water

was rendered opalescent, both by the pronitrate and pernitrate of mercury, but not by the third mercurial salt; but this third salt produced a slight opalescence in a solution of one part of muriatic acid in 3,552,000 parts of water.

3. Arsenic. Some discussions have taken place in Germany respecting the best test for white arsenic. Gärtner observed that the formation of Scheele's green, by pouring cuprated ammonia into the liquid containing the white arsenic, does not in certain circumstances take place. Schweigger recommends sulphureted hydrogen, which is certainly a most delicate test of arsenic, in consequence of the fine yellow precipitate which it forms. The employment of nitrate of silver as a test for arsenic does not seem to be known in Germany. This test, first pointed out by Mr. Hume, but much simplified and improved by Dr. Marcet, is certainly very delicate; and, when the precautions suggested by Dr. Marcet are attended to, does not seem liable to ambiguity.

4. Manganese.-Pfaff has published a set of experiments on the method of separating manganese from iron, and has shown that all the methods hitherto proposed on the Continent are imperfect. Bergman's process has been long given up by all chemists. Vauquelin's, by means of bicarbonate of potash, he found likewise unsuccessful. The method by means of tartrate of potash is incomplete, because the tartrate of potash-and-manganese is soluble in water. Dr. John's method, by oxalate of ammonia, was like. wise unsuccessful. Nor did he succeed better by means of the succinates, benzoates, or phosphates. Mr. Hatchett's method of separating the iron, by means of ammonia, was not tried. I find that by means of it I can very easily procure perfectly pure oxide of manganese. Whether it would succeed equally in forming an accurate separation of manganese and iron for the purposes of analysis, I have not tried; though I think it probable that it might be used for that purpose with advantage, supposing iron and manganese to be the only substances in the solution upon which we operate.

5. Iron. Mr. Porrett has recommended triple prussiate of potash, or ferrureted chyazate of potash, as he calls it, as the best method of throwing down iron, and ascertaining its quantity. The precautions necessary to be attended to are the following. The ferrureted chyazite must be pure. There must be no excess of acid in the solution, or as little as possible. All other substances precipitated by the ferrureted chyazate must be previously removed. The ferrureted chyazate must not be added in excess, or as little so as possible. The solution being boiled, and the Prussian blue separated and weighed, every hundred parts of it must be considered as equivalent to 34 235 of peroxide of iron in the solution.

I have no doubt that when no manganese is present the ferrureted chyazate may be employed with considerable accuracy to detect the quantity of iron in any substance under analysis; but as it most frequently happens in mineral analysis that iron and manganese are

mixed together in unknown proportions, ferrureted chyazate of potash cannot be employed in such cases till a good method is discovered of separating manganese from iron. Gehlen's method is the best hitherto proposed; though it only answers when the whole of the iron is in the state of peroxide.

I may mention here, for the sake of our British manufacturers of sulphuric acid, that E. W. Martius announced in 1811, in a German journal, that he had found white arsenic in a glass carboy of English sulphuric acid. The arsenic had separated from the acid, and formed a crust in the inside of the glass. As the notice merely states the fact of the separation of white arsenic, I conceive it possible that Martius might have been mistaken. If his statement be accurate, the arsenic must have made its way into the carboy by some odd accident or other; for I think it hardly possible that it should have been mixed with the sulphur before its combustion.

VI. Acids.

1. Formic Acid.-The reader is probably aware that this acid, which exists ready formed in red ants, was originally discovered by Ray and Fisher; that it was first accurately examined by Margraaf; that Arvidson and Oern published a very complete set of experi ments on it in 1777 It continued to be considered as a peculiar acid till Fourcroy and Vauquelin published a set of experiments on it in 1803, and drew as a conclusion from them that it is not a peculiar acid, but a mixture of the acetic and malic acids. This dissertation convinced all the French chemists; and induced me in the second edition of my System of Chemistry to expunge. it from the list of acids. But Suerzon having published a new set of experiments on it, in 1805, showed that the premises of the French chemists were insufficient to warrant their conclusions, and that formic acid possessed striking and essential properties which distinguished it from acetic acid. I suggested in my System the propriety of a more rigid examination of the formates than had hitherto taken place. This seems to have induced Gehlen to undertake a laborious set of experiments on the subject. He observes in the outset, that if I had been acquainted with the experiments of Arvidson and Oern, and of Richter, on the formales, I should probably have been satisfied, without requiring any farther proofs. I regret that it has never been in my power to peruse either of the works alluded to by Gehlen. My knowledge of the experiments of Arvidson and Oern is derived from the account of them given by Keir in his Dictionary, and by Bergman in his Treatise on Elective Attractions. Gehlen's experiments are quite decisive; but they are, unfortunately, too long to be detailed here. He prepared, in the first place, formate of copper, from which he separated the formic acid by distilling it with sulphuric acid in a retort. He compared the pure formic acid thus obtained with acetic acid, procured from acetate of lead by a similar process.

Thus prepared, it has an acid, and peculiar taste and smell, quite different from that of acetic acid. When cooled down sufficiently, it becomes solid, but does not crystallize. Its specific gravity was 11168; and, when diluted with its own weight of water, the specific gravity becomes 1·060; and when with twice its weight of water, it becomes 1·0296. In all these respects acetic acid is very different. It likewise requires different proportions of bases to neutralize it. Gehlen describes minutely the formates of copper and barytes, and compares them with the acetates of the same bases. They differ in colour, solubility, form of crystals, and all their other properties, from each other.

2. Ferrureted Chyazic Acid.-Mr. Porrett has discovered two new acids, and rendered it probable that many more exist. Ferrureted chyazic acid is obtained from the salt formerly called triple prussiate of barytes. This salt is dissolved in water, and as much sulphuric acid added as is just sufficient to neutralize the barytes present. The mixture, being agitated in a phial, is set aside for some time. Sulphate of barytes precipitates, and the ferrureted chyazic acid remains in solution in the liquid. Its properties are as follows:

It has a pale lemon colour; but no smell. It is decomposed by a gentle heat, or by exposure to a strong light. Prussic acid is then formed, and white triple prussiate of iron, which is soon changed into Prussian blue. It separates acetic acid from all its combinations. It combines with the different bases, and forms the salts formerly called triple prussiates. This acid is composed of four constituents; namely, black oxide of iron, carbon, hydrogen, and azote; or perhaps it would be as well to consider it as composed of five constituents, oxygen, iron, carbon, hydrogen, and azote. It would be a curious, but very difficult problem, to determine the proportions in which these different constituents are united in this complicated acid. How many atoms of each enters into it. From the great permanency of this acid when compared with some of the vegetable and animal acids, one would be disposed to suspect that its composition is very simple. Perhaps an atom of each constituent would not be very far from the truth.

According to Mr. Porrett, ferrureted chyazate of potash is composed of

Black oxide of iron..17.26 Ferrureted chyazic acid.. 47.66 Prussic acid.... ..30.10 S

Potash

Water

39.34

13.00

100.00

This analysis cannot be reconciled with the supposition of ferrureted chyazic acid being a compound of an atom of each of its constituents. If we suppose the salt composed of an atom of acid and an atom of base, as is usual with the salts of potash, then an