composed of an atom of sulphate of lead and an atom of hydrated peroxide of copper (C Aq2 + Pb S2). Is it not equally possible that hydrated peroxide of copper may combine, under favourable circumstances, with acetate of copper? It may be objected that the quantity of water is greater than is required to form a hydrate; but such also is the constitution of the combinations of oxide of zinc and of magnesia already alluded to, and it is surely not assuming too much to admit an excess of water which is only double the water of crystallization contained by the two compounds when separate. On this supposition, the formula for the constitution of verdigris would be Cu Ã2 + Cu Aq1o, instead of Cu A + 6 Aq.* We may add, that if the constitution of verdigris were correctly represented by the latter simple formula, it would be difficult to expect so remarkable a mobility among its constituents, that the weakest chemical force disunites then, and causes them to combine in different proportions 4. Black Sub-acetate of Copper. When the soluble sub-salt is heated in a dilute solution, it deposits a flocky liver-brown coloured substance, which, when received upon a filter, washed, and dried, appears black, and soils strongly every thing with which it comes in contact. This substance passes readily through the filter, and renders the water turbid whenever we begin to wash it. If it be washed so long as the water continues to dissolve out any copper, and if the filtered liquid be evaporated to dryness, there is left upon the glass a thin, transparent, colourless film, resembling a coating of varnish. This proceeds from the brown salt, which had been dissolved by the water. If it be prepared by boiling verdigris or the insoluble subsalt in water, the filtered liquid is more easily obtained transparent; but, in this case, a portion of the insoluble green salt always escapes decomposition, and remains, therefore, intermixed with the precipitate. 100 parts of this black subsalt dried in a temperature of 150°, on being analyzed by hydrate of barytes, and by precipitating the copper with a plate of iron, yielded from 5-6 to 5-7 parts of sulphate of barytes, and from 91.6 to 92.5 parts of peroxide of copper. In another experiment, in which the salt was decomposed with sulphuric acid, I obtained 183.95 parts of sulphate of copper 91.46 peroxide of copper. The mean of these analyses indicates 92 per cent. of peroxide of copper, whose oxygen * I think it probable that compounds may hereafter be formed containing a still larger proportion of hydrated oxide of copper; for in the verdigris which I prepared, I observed portions of an intense and pure dark blue colour, whose quantity, however, was too inconsiderable for purposes of an analytical examination. is 18.55. 5-6 parts of sulphate of barytes are equivalent to 2.45 parts of acetic acid, whose oxygen is 1.151; but 1.151 x 16 = 18-416. For the water there remains 5.55, whose oxygen is 4.934: this again is only a very little more than four times the oxygen of the acetic acid, or one-fourth of that of the peroxide of copper. This salt is therefore composed of The following is a summary of the results to which I have been conducted by the experiments detailed in this memoir. 1. Acetic acid is capable of combining with peroxide of copper in the following proportions: 1. Neutral acetate of peroxide of copper Cu A2 + 2 Aq 2. Blue verdigris. 3. Soluble subsalt 4. Insoluble subsalt = 5. Black or brown subsalt.. Cu24 A + 12 Aq If the quantity of base in the neutral salt be regarded as unity, its quantity in the others, when compared with the same quantity of acid, will be found to constitute multiples of the unit by the numbers 1, 2, 3, and 24 (48 ?). In the first salt, the base is combined with twice as much acid as in the second; and in the third, with twice as much as in the fourth. 2. Of all these salts the second has the simplest composition, and consists, if the calculation be made directly from the weight of its component parts, of the simplest number of atoms; but it possesses a property which is directly contradictory of this supposed simplicity of constitution, for its ingredients are retained in union by weaker affinities than in any of the other combinations of acetic acid and peroxide of copper, and have a greater tendency to separate, and to recombine in other proportions. A temperature of 140° decomposes it, with the loss of a portion of its chemically combined water, into an atom of the first and an atom of the fourth salt. A sufficient quantity of cold water decomposes it into an atom of the first, an atom of the third, and two atoms of the fourth salt; and a sufficient quantity of boiling water decomposes it into a large number of atoms of the first salt, and a very few of the fifth. From all these circumstances, together with this, that in the salt the oxygen of the acid is not a multiple by a whole number, but by 1 of the oxygen of ' the base, it appears probable that the blue variety of verdigris does not possess so simple a constitution as is indicated by the foregoing formula, but that it may be a compound of the first salt with hydrated peroxide of copper and water of crystallization; on these grounds, its composition would, perhaps, be more accurately represented by the formula Cu A+ Cu Aq2 + 10 Aq, in the last term of which, the water of crystallization is distinguished from the portion which acts as an acid when in combination with the peroxide of copper. ARTICLE VII. Reply to M. Vauquelin's Remark on a supposed Contradiction in Dr. Thomson's System of Chemistry. (To the Editors of the Annals of Philosophy.) GENTLEMEN, Glasgow, Aug. 10, 1824. ON my return home yesterday from Berwickshire, I found the number of your journal for the present month lying on my table. My attention was naturally attracted to the notice in p. 147 translated from the Ann. de Chim. and entitled "Note on a Contradiction in Thomson's System of Chemistry respecting Phosphuretted Hydrogen Gas. By M. Vauquelin.' M. V. observes, that I state in the first place that phosphuretted hydrogen contains its own volume of hydrogen united to a volume of phosphorus vapour; that when it is exposed to the direct rays of the sun, a quantity of phosphorus is deposited, and bihydroguret of phosphorus obtained; and that when sulphur is heated in bihydroguret of phosphorus, the bulk is doubled, and two volumes of sulphuretted hydrogen obtained. M. Vauquelin theu goes on to show, that these two statements are inconsistent with each other, and that when sulphur is heated in phosphuretted hydrogen gas, only a very slight increase of bulk takes place. He mentions also that the deposition of phosphorus takes place without any exposure to the sun's rays, and more rapidly during the night and in a dark place than during the day. Had M. Vauquelin paid attention to the account which I have given of bihydroguret of phosphorus in the passage of my System of Chemistry which he quotes, he would have seen the cause of the apparent contradiction which he notices. It is owing to my having supposed that phosphuretted hydrogen gas, when altered by keeping, is converted into the gas which Sir H. Davy obtained by heating hydrated phosphorous acid, and which he described in Phil. Trans. for 1812, p. 408. To this account I referred in my System, thus pointing out the source whence I derived my knowledge of the properties of bihydroguret of phos phorus. Davy found that the bulk of this gas was doubled when potassium was heated in it, or when sulphur was sublimed in it. He states that three volumes of it require for complete combustion more than five volumes of oxygen gas; and that it is a compound of one part by weight of hydrogen and five parts of phosphorus. Now this (when the requisite corrections are made) is the same as if he had said that it is a compound of two atoms hydrogen and one atom phosphorus. In consequence of these statements of Davy, I thought myself entitled to conclude that the gas which he described was a compound of two atoms hydrogen and one atom phosphorus, and I called it in consequence bihydroguret of phosphorus. I had myself determined by experiment that when phosphuretted hydrogen gas is left for some time over water or mercury, it deposits phosphorus without any perceptible alteration in its bulk, loses the property of burning spontaneously when mixed with atmospheric air, and yet still continues a compound of phosphorus and hydrogen. Hence I inferred that it had become the identical gas described by Davy. But I made no experiments on the effect produced on it by potassium and sulphur, relying on the accuracy of Davy's statements. But I still considered that it would be necessary to determine the point by direct experiments; and more than two years have elapsed since I set about examining the subject. I left a quantity of pure phosphuretted hydrogen in a graduated glass jar over mercury for six months; namely, from January to August. The mercurial trough was placed nearly in the middle of my laboratory, which is a large room, and so that the sun never shone on the gas. Another jar filled with the same gas was placed over mercury in the dark, and left for the same length of time. But it must have been accidentally overturned, and again replaced by some person; for when I examined the gas, I found it to be common air. The gas standing in the middle of the laboratory had not sensibly altered its bulk; but a portion of phosphorus had been deposited on the inside of the jar. It did not burn when mixed with common air or oxygen gas; but still had the peculiar smell which characterizes phosphuretted hydrogen gas. Its bulk was not in the least altered by subliming sulphur in it, so that in this respect (as Vauquelin states) it resembles phosphuretted hydrogen, and differs from Davy's gas. One volume of it required for complete combustion 1 volume of oxygen gas. When a volume of it is mixed with 0.75 volume of oxygen, and an electric spark is passed through the mixture, detonation takes place, and the oxygen disappears; but the residual gas is within one-seventh of a volume, and on adding another half volume of oxygen gas, it may be detonated again, and the whole disappears. Thus it cannot be consumed completely by two different proportions of oxygen gas, which distinguishes it from phosphuretted hydrogen gas. The effect produced by subliming sulphur in this gas shows that it contains its own volume of hydrogen gas. Hence the hydrogen in a volume of it will require for combustion half a volume of oxygen gas. The remaining 0.75 volume of oxygen gas must have combined with the phosphorus vapour, and converted it into phosphoric acid. Now phosphorus vapour requires for this its own volume of oxygen gas. Thus it is evident that phosphuretted hydrogen gas when left standing over mercury loses one-fourth of its phosphorus, and becomes a compound of ... Sp. gr. 0.0625 1 volume bydrogen gas. 0.6875 So that its specific gravity is reduced from 0.9027 to 0.6875, and it contains just ten times as much phosphorus by weight as of hydrogen. It is a compound of 4 atoms hydrogen and 3 atoms phosphorus. M. Vauquelin will see from the above statement that the gas in question is not the same as Davy's gas to which I gave the name of bihydroguret of phosphorus (a harsh term, but expressive of the composition of the gas). We may call it, for the sake of distinction, subphosphuretted hydrogen gas. Thus phosphorus and hydrogen gas unite in at least three proportions; viz. Hydrogen. Phosphorus. 1. Phosphuretted hydrogen composed of... 1 atom + 1 atom 2. Subphosphuretted hydrogen. +3 4 On an Anomaly presented by the Combination of Potassium and Oxygen; with some general Observations on Combination. By the Rev. J. B. Emmett. (To the Editors of the Annals of Philosophy.) GENTLEMEN, Great Ouseburn, Aug. 6, 1824. IN estimating the specific gravity of oxygen as it exists in different solid compounds, potash presents a remarkable pheno |