REMARKS. Sixth Month.-1-8. Fine: clear, and very warm. 9. A few drops of rain about six, p. m.: some lightning from 11 to 12, p. m. 10. Fine: a heavy thunder storm in the evening. 11-13. Fine: hot. 14. A shower at three, p. m. 15. Showery. 16. Fine. 17. Cloudy. 18-22. Fine. 23. A slight shower about nine, a. m. with some distant thunder. 24. Fine: a heavy shower about two, p.m. 25–27. Fine. 28. Cloudy. 29. Fine: cloudy: a heavy shower about 10, p. m. 30. Cloudy and fine. RESULTS. Winds: N, 7; NE, 4; E, 2; SE, 7; S, 2; SW, 4; W, 2; NW, 1; Var. 1. Barometer: Mean height For the month... For the lunar period, ending the 12th...... 30.119 inches. 30.167 For 14 days, ending the 12th (moon south) .......... 30-187 For 12 days, ending the 24th (moon north). ....... 30.087 Daniell's Hygrometer for Fifth Month (omitted last month).—1st, 20; 3d, 20; 4th, 13; 6th, 6; 7th, 3; 8th, 15; 10th, 3; 11th, 24; 13th, 6; 14th, 18; 15th, 13 16th, 15; 17th, 21; 18th, 15; 20th, 20; 21st, 22; 22d, 10. Laboratory, Stratford, Seventh Month, 12, 1822. R. HOWARD ANNALS. OF PHILOSOPHY. SEPTEMBER, 1822. ARTICLE I. On the Composition of Common Verdigris. IN the Annals of Philosophy, vol. i. p. 417 (New Series), I gave an analysis of crystallized verdigris, sometimes, but improperly, called distilled verdigris. From the experiments which I detailed, it appears to be a compound of two atoms of acetie acid, one of peroxide of copper, and three of water; or in other words, of one atom of binacetate of copper combined with three atoms of water of crystallization. Soon after I had completed that analysis, I began an examination of common verdigris, usually termed subacetate of copper, but some difficulties occurred which induced me to discontinue the experiments. It is well known that when a small quantity of water is added to a fragment of common, verdigris, it softens and swells by imbibing the water, and if more be added, a blue solution is obtained, while a portion of the verdigris remains undissolved. It appeared to me at first probable that common verdigris might be a mixture of binacetate and subacetate of copper; the former dissolving and forming the blue solution, and the latter remaining undissolved. Upon examination, however, I could not find this to be the case, and one circumstance appeared unfavourable to such a supposition. When the verdigris in question is closely examined, it is found to contain small crystals, which, instead of being distinctly formed, and of a green colour, as is the case with the binacetate, are acicular, of a light. blue colour and silky lustre. New Series, VOL. IV. M In the state in which this compound is usually met with, it is very difficult, on account of its extreme compactness, to determine whether it consists principally of these blue crystals, or whether they are merely mixed with some other acetate, or with hydrate of copper. During a visit to Birmingham in the latter part of last year, Mr. Badams, a manufacturer of both kinds of verdigris, showed me some light blue crystals of acetate of copper, which, he informed me, were common verdigris that had not been subjected to pressure by putting it into bags. Being desirous to ascertain the composition of these crystals, Mr. Badams was good enough to supply me with a quantity for analysis, and I shall now state the results of the experiments which I made upon them, and also upon common verdigris. Although these blue crystals appeared to be unbroken, their size was too minute to allow of their form being determined; they are unalterable by exposure to the air, and so very light that 100 grains, when not pressed together, occupy the space of an ounce of water. When a small quantity of water is added to these crystals, they absorb it, precisely as common verdigris does; to determine the action of a large quantity of water, I put 100 grains of the crystals into a pint of it, and after occasionally agitating the mixture, the clear solution was poured off. To the insoluble residuum, half a pint of water was added; it gradually became brown, and at the expiration of three days, it had the appearance of being completely decomposed. It appears then that the blue crystals are separable by water into a soluble acetate, and one which is insoluble, and that the latter is decomposed even by cold water. I now attempted by direct experiment to ascertain the quantity of water which these crystals contain. With this view, 100 parts were heated in a platina crucible to the temperature of boiling water. They became of a green colour, and lost 24 parts: as, however, a portion of this loss was evidently derived from the expulsion of acetic acid, it was impossible to determine the quantity of water by direct means. To find the quantity of acetic acid, 100 parts of the crystals were boiled in water with lime. Carbonic acid gas which had been previously sent through water, was passed into the filtered solution to precipitate the excess of lime; the solution, after being heated to expel the superfluous carbonic acid, became neutral acetate of lime, and was decomposed by carbonate of soda; the carbonate of lime precipitated, being washed and dried, weighed 28.3 parts. This experiment was repeated with but little variation in the result. To ascertain the proportion of peroxide of copper, 100 parts of the blue crystals were heated in a platina crucible with dilute nitric acid; when the nitrate of copper formed was decomposed by a red heat, the peroxide left, weighed 43.2 parts. This experiment being repeated, using a flask instead of the crucible, 43.3 parts were obtained, giving a mean of 43.25 of peroxide of copper. According to Dr. Thomson's latest experiments, the number representing hydrogen being 1, that of acetic acid is 50, and carbonate of lime being also 50, the quantity obtained in the experiments above detailed will indicate that of the acetic acid in 100 parts of the blue crystals, or 28-3 per cent. which, being added to 43-25 of peroxide of copper, will give as the composition of these crystals, Now an atom of acetic acid being 50, that of peroxide of copper 80, and of water 9, it will appear that these blue crystals of acetate of copper are by theory composed of I have already observed that these crystals are readily decomposed by water, and its effects upon the salt are sufficiently marked to merit particular notice; a small quantity of water being added to 100 grains of the crystals, the whole became a pulpy mass. When the water was increased to a pint, a blue solution was obtained, and a greenish precipitate thrown down. Upon examining this blue solution, it was found to consist of binacetate of copper, and the green precipitate of subacetate, composed of one atom of acid and two atoms of oxide. It is, therefore, evident, that in addition to the acetate and binacetate of copper already described, there exists a subacetate composed of One atom of acetic acid. . 50 Two atoms of peroxide of copper 80 × 2 160 210 When this subacetate was diluted with a further quantity of water, it became, as I have already noticed, quite brown in a few days; but whether it was totally decomposed into peroxide, or was another subsalt, I have not examined. Having now ascertained that a compound of one atom of acetic acid and oxide of copper actually existed, I proceeded to examine whether common verdigris consists entirely of it, or is a mixture of different compounds. For this purpose, I reduced 100 parts of French common verdigris to powder, and boiled it with excess of lime, filtered the solution, passed carbonic acid through it, decomposed it by carbonate of soda, and collected the carbonate of lime in the mode already described. The mean of two experiments carefully performed gave 29.3 of carbonate of lime, equivalent to a like quantity of acetic acid. The quantity of oxide of copper was ascertained by boiling 100 parts of the verdigris in dilute sulphuric acid. Two parts of insoluble impurity were left, and the sulphate of copper being decomposed by heating with excess of potash, gave 43.5 of peroxide of copper. This experiment was repeated without any variation. The composition of French verdigris is, therefore, as follows: That this is the true composition of common verdigris, and that it is essentially composed of the crystals which I have already described, was further proved by subjecting the verdigris manufactured by Mr. Badams, and in its compressed state, to a similar examination. This I found to consist of The action of water upon both these specimens of verdigris is perfectly similar to that upon the blue crystals of acetate of copper; indeed, from the following comparative statement, it will appear, except in containing less water, occasioned by artificial drying, that when deprived of insoluble matter, the three substances resemble each other as perfectly as could be expected. |