If 24,1 grains of this precipitate correspond to 10 grains of sulphate of potash, 17,2 grains of it correspond to 7,14 grains of this salt. It has been seen (n) that 10 grains of the saline part of this volcanic salt would have afforded 12,55 grains of sulphate of barytes. But 7,14 grains of sulphate of potash form only 9,42 grains of sulphate of barytes,* and therefore the remaining 3,13 grains of sulphate of barytes would be produced by the sulphate of soda, and correspond to 1,86 grains of it in an arid state, or uncombined with ice.† 10 grains of the saline part of this native salt would have produced 1,12 grains of ignited muriate of silver (k). By accurate experiments 241 grains of ignited muriate of silver have been found to correspond to 100 grains of ignited muriate of soda. ‡ Consequently the soluble portion of the present Vesuvian salt consists of t. The insoluble sandy residue (g) having been thoroughly * Dr. MARCET on Dropsical Fluids. + Prof. KLAPROTH's Essays, Vol. I. p. 282. Dr. HENRY, Phil. Trans. 1810. edulcorated, dilute nitric acid was put to it. A green solution formed without any effervescence. Acetate of barytes scarcely rendered this solution turbid; but nitrate of silver produced a copious curd-like precipitate, and iron abundantly threw down copper from it. The green grains enclosed in this native sulphate of potash, appear, therefore, to be a submuriate of copper, of the same species as that of the green sands of Peru and Chili. Muriatic acid dissolved the yellow ochraceous powder, and prussiate of soda-and-iron produced Prussian blue. I am inclined to believe this yellow powder to be a submuriate of iron, but its small quantity, and the admixture of the submuriate of copper, were impediments to entirely satisfactory results. Such a submuriate of iron, though, if I mistake not, overlooked by chemists, exists, for the precipitate which oxygen occasions in solution of green muriate of iron, contains marine acid.. Possibly this yellow powder, and the crystals of speculary iron which exist in this Vesuvian salt, have been produced by a natural sublimation of muriate of iron, similar to that of the experiment of the Duke d'AYEN, recorded by MACQUER,* and which was known long before to Mr. BOYLE and Dr. LEWIS.+ This Vesuvian salt, considered in its totality, has presented. no less than nine distinct species of matters, and a more rigorous investigation, than I was willing to bestow on it, would probably add to their number. July 3, 1813. Dict. de Chemie, Art. Fer. ↑ A course of practical chemistry by WILLIAM LEWIs, 1746, page 63, note:ƒ.. XXXI. Some Experiments and Observations on the Substances produced in different chemical Processes on Fluor Spar. By Sir Humphry Davy, LL.D. F. R. S. V. P. R. I. N Read July 8, 1813. In the Bakerian Lecture, for 1808, I have given an account of an experiment on the combustion of potassium in silicated fluoric acid gas, in which the gas was absorbed, and a fawn. coloured substance formed, which effervesced with water, and left, after its action on that fluid, a residuum which burnt when heated in oxygen, reproducing silicated fluoric acid gas; and I concluded from the phenomena, that the acid gas was decomposed in the process, that oxygen was probably separated from it by the potassium, and that the combustible substance was a compound of the siliceous and fluoric bases. The experiment of burning potassium in silicated fluoric acid gas was made likewise by M. M. GAY LUSSAC and THENARD, before I published any account of my researches on this phenomenon. It was indeed one of the most obvious applications of potassium, and it occurred to many others, as well as to myself, that it might be made, immediately after I discovered that metal. M. M. GAY LUSSAC and THENARD drew the same conclu-sions as I did, namely, that the acid gas was probably decomposed during the action of potassium on silicated fluoric acid; but their general views differed from mine in this respect, as they supposed, that no part of the inflammable matter was derived from silica, and they likewise reasoned on the phenomena with more caution. At the time that my conclusions were drawn, I was ignorant of the true nature of the muriatic acid. After I had tried in vain to decompose oxymuriatic gas, and after I had found that the compounds of this substance with phosphorus, sulphur, and the metals combined with ammonia without any decomposition, and produced compounds in which no oxygen could be discovered; I was forcibly struck by the analogy between the oxymuriatic and the fluoric compounds, and led to doubt of the justness of my ideas respecting the nature of fluoric acid. I tried an experiment on the comparative quantities of fluate of lime, formed from equal volumes of silicated fluoric acid gas, one of which had been acted upon by potassium, and then exposed to solution of ammonia, the other had been absorbed by solution of ammonia: and I found the proportion of calcareous fluate nearly one-third larger in the latter case. This result at first seemed favourable to my early ideas, that the acid contained a peculiar inflammable basis, which was separated by the potassium, and existed in the combustible substance insoluble in water; but it could not be considered as decisive on the question, for, it occurred to me as possible, that this substance might be silicum, or the basis of silica united to a much smaller proportion of the fluoric principle, than that existing in silicated fluoric acid. During the period that I was engaged in these investigations, I received two letters from M. AMPERE, of Paris, con taining many ingenious and original arguments in favour of the analogy between the muriatic and fluoric compounds. M. AMPERE Communicated his views to me in the most liberal manner; they were formed in consequence of my ideas on chlorine, and supported by reasonings drawn from the experiments of M. M. GAY LUSSAC and THENARD. Before I enter upon the detail of the investigations which promise to elucidate the nature of the fluoric compounds, it will be right to describe those substances produced from fluor spar, which have been the principal objects of my experiments, and to mention the different hypothetical views that may be formed respecting them. The first of these substances is the silicated fluoric acid gas, which was discovered by SCHEELE, and examined in its pure state by PRIESTLEY. It is formed by heating a mixture of fluor spar, powdered glass, and sulphuric acid. It is a very heavy elastic fluid, its specific gravity being nearly forty-eight times as great as that of hydrogen. It produces, according to my brother Mr. JOHN DAVY, a quantity of silica equal to 15 of its own weight by its action upon water, and a quantity equal to 64 of its weight by its action upon solution of ammonia. It condenses twice its own volume of ammonia, and forms a solid salt, volatile when free from water without decomposition. 1000 Liquid fluoric acid, the second of these substances, was discovered by SCHEELE, but first obtained in its pure form by M. M. GAY LUSSAC and THENARD. It is procured by heating concentrated sulphuric acid and pure fluor spar, in retorts of silver or lead, and receiving the product in receivers of the same metals artificially cooled. It is a very active substance, and |