_Protosulphuret._ This compound is obtained whenever a neutral solution of cobalt is treated with hydrosulphuret of lime, &c. or it may be obtained from any acid solution by first precipitating the blue oxide by an alkali, and then introducing sulphuretted hydrogen into the mixture. By this last method I found a solution previously known to contain 44 parts by weight of protoxide to absorb 15 parts of sulphuretted hydrogen; when filtered and dried in a heat of 100° it yielded 51 parts of protosulphuret. In appearance it resembles many of the other black sulphurets. It consists of 100 cobalt and 38 sulphur; Proust finds 40 sulphur, but he considers it only an approximation. The same sulphuret may be formed by heating the oxides of cobalt and sulphur together to a red heat; at least a combination is effected as Proust observed, but I have not investigated the proportions. Sulphur does not seem to combine with the metal in this way. _Deutosulphuret_ ... _dodecasulphuret_. When the recently precipitated and moist oxide of cobalt, the neutral muriate, or acid muriate of cobalt, as well as other salts of the same, are treated with dilute quadrisulphuret of lime, sulphurets of cobalt are formed in various proportions according to the ingredients, from the deutosulphuret to the dodecasulphuret: these precipitates are all black and not easily distinguished in appearance; but there is reason to believe they are true chemical compounds. 34. _Sulphurets of manganese._ Though sulphur and manganese do not unite directly, they can be brought into union by intermediate bodies, both in the dry and humid way. _Protosulphuret._ This compound may be formed by heating to a low red, a mixture of the oxide of manganese and sulphur, or of the white carbonate of manganese and sulphur; or it may be formed by treating a solution of manganese by a hydrosulphuret, (sulphuretted hydrogen not producing any precipitate); this last method seems to produce a dry hydrosulphuret of manganese, which being heated to red nearly, parts with water and a little sulphur and there remains the protosulphuret. The protosulphuret is of a snuff brown colour; but the hydrosulphuret, when recently precipitated is of a light drab colour, which grows deeper when exposed to the air, and when dried becomes brown like the protosulphuret; when heated, the colour is not much changed. The hydrosulphuret of manganese gives sulphuretted hydrogen by cold muriatic acid, and the protosulphuret gives the same by the acid heated. The proportion of the elements in the protosulphuret may be inferred from the fact that the black oxide yields its own weight of protosulphuret; that is, 156 grains, composed of 100 metal and 56 oxygen give 156 of sulphuret; hence the atom of metal, 25, unites with one of sulphur, 14. I found 32 of the protoxide in solution unite to 15 of sulphuretted hydrogen to form 47 hydrosulphuret dried in 100°. This lost about 8 parts or rather upwards by heat.