It may be proper to subjoin the results of others, who have investigated the oxides of manganese. Bergman finds 3 oxides, containing 100 metal + 25, 35, and 66.6 oxygen; Dr. John finds 3 oxides, containing 100 metal + 15, 25, and 40 oxygen: Berzelius finds 5 oxides, containing 100 metal + 7, 14, 28, 42, and 56 oxygen; and Davy finds 2 oxides, containing 100 metal + 26.6, and 39.9 oxygen, respectively.
23. Oxides of chromium.
There appear to be at least two oxides of chromium, one or other of which is found in combination with the oxides of lead or iron, but hitherto so very sparingly that few chemists have had an opportunity of investigating the proportions of chrome and oxygen, in the oxides of chromium. The chief sources for information on this subject, are essays by Vauquelin, An. de Chimie, Vol. 25 and 70; by Tassaert, ibid. 31; by Mussin Puschin, ibid. 32; by Godon, ibid. 53; by Laugier ibid. 78, and by Berzelius, Annal. of Philosophy, 3.
The oxides of chromium, as might be supposed, are distinguished for the colours which they possess and impart to the compounds into which they enter. One of the oxides is green; it gives colour to the emerald. The other is yellow, dissolved in water, but deep red when crystallized, and possesses the characters of an acid; it unites with alkalies, earths, and metallic oxides; it was first found in Siberia, in combination with the oxide of lead, a salt now denominated chromate of lead, of a splendid yellow colour, inclining to orange or red. Since then, the chromate of iron, has been found in France, America, and Siberia, with a prospect of greater abundance.
In order to investigate the weight of the atom of chromic acid, it is necessary to attend to such of the chromates as have been carefully examined. The chromates of potash, barytes, lead, iron, and mercury, are those with which we are best acquainted.
Vauquelin has given us the components of the native chromate of lead by analysis, and those of the artificial chromate by synthesis; the results do not accord very nearly: for, according to the analysis corrected by the modern science,
| Chromate of lead | = | 62 | acid | + 97 oxide |
| By synth. chromate of lead | = | 57½ | — | + 97 — |
Berzelius however, has more lately given us the results of his experience, both analytical, and synthetical; and he finds both to give chromate of lead nearly = 44 acid + 97 oxide.
| Chromate of barytes | (Vauq.) | = | 47.8 | acid | + | 68 | barytes |
| Ditto | (Berz.) | = | 44 | — | + | 68 | — |
| Native chromate of iron | (Vauq.) | = | 45 | acid | + | 35½ | oxide |
| Ditto | (Laugier) | = | 55 | — | + | 35½ | — |
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,