Having received a small portion of chromate of potash in solution, from a chemical friend (J. Sims), I endeavoured to satisfy myself, as far as my materials would go, as to the nature and proportions of the chromates. The solution was of the sp. gr. 1.061, and consequently in 100 measures contained nearly 6.7 grains of chromic acid and potash, &c.--The liquid was a beautiful yellow; it was alkaline by the colour test. By the usual tests, I had reason to believe, that the solution contained as under per cent.--namely, 2.2 gr. chromic acid 2. potash .8 uncomb. potash 1.4 carb. potash .3 sulphate of potash --- 6.7 With this liquid neutralized by nitric acid, I formed the chromates of lead, barytes, iron, and mercury; and I am inclined to believe these salts are nearly constituted as under: Neutral chromate of potash 46 acid + 42 potash -- -- of barytes 46 -- + 68 barytes -- -- of lead 46 -- + 97 oxide -- -- of iron 46 -- + 32 oxide (black) -- -- of mercury 46 -- + 174 oxide (black) According to these results, the atom of chromic acid weighs 46; it is made 44 by the results of Berzelius, and from 45 to 62 by those of Vauquelin; I would not be understood to place great confidence in the above results of mine, though I am persuaded they will be found good approximations. Is the chromic acid the deutoxide, or the tritoxide of chromium? The determination will evidently be affected by the question, how much oxygen must be abstracted from the chromic acid to reduce it to the green oxide. Vauquelin finds 46 acid to lose 6½ oxygen, and Berzelius 10½, when converted into green oxide by heat. From the former of these, one would infer chrome to be 32, the green or protoxide of chrome to be 39, and the acid or deutoxide 46: from the latter, chrome = 25, protoxide = 32 (unknown), the green oxide = 1 protoxide and 1 deutoxide united [= 71 = 50 chrome + 21 oxygen = (25 chrome + 10½ oxygen) × 2 = 35½ × 2] the deutoxide = 39, and the tritoxide or chromic acid = 46. I have not had an opportunity to perform any experiment that appears to me decisive as to the accuracy of one or other of these views; but shall make a few remarks relative to them.