On the Combinations of Chromium. 137 



solve oxide of chromium, either when moist or dry ; — hydrate 

 of chromium may be suspended in ammonia, but after a few 

 days it precipitates, when the mixture is kept in closed ves- 

 sels. It is readily obtained by washing the orange colored 

 chromate of lead of commerce, in a large quantity of distilled 

 water ; collecting and drying the powder, and mixing it with 

 oil, so as to form a paste ; placing the paste in a covered cru- 

 cible, and exposing it to a red heat for twenty minutes ; — 

 agitating it occasionally, to collect the reduced lead into a 

 globule. On withdrawing and cooling the crucible, a dark 

 green oxide, mixed with small globules of lead, and a button 

 of reduced lead are obtained. The former separated from 

 the lead by washing, and mixed with three parts of nitre, 

 and exposed in a crucible for half an hour to a full red heat, 

 gives on cooling, a yelloAv salt — which is to be dissolved in 

 water, and neutralized by adding sulphuric acid, until turme- 

 ric paper browned by ammonia, is restored to its former color, 

 by the solution — a small quantity of ammonia added will 

 precipitate any alumina, and the filtered solution, mixed with 

 a quantity of sulphuric acid, equivalent to one half the nitre 

 employed, and heated to 212° F., will afford a rich green pre- 

 cipitate, on adding pure ammonia, containing, after washino- 

 with water, nothing but protoxide of chromium and water. 

 It is essential to the perfection of this process, that the nitre 

 should be decomposed into a nitrite, and chromate, by the 

 temperature to which it is exposed ; but the native mixture 

 of oxides of chromium, and iron, may be employed as a sub- 

 stitute, for the bichromate of lead. 



Dcutoxide of Chromium. — Its color is brownish black, in 

 fragments, its lustre shining. In cold muriatic acid, it dis- 

 solves and forms a greenish brown solution ; when the solu- 

 tion is heated, chlorine is evolved, and protomuriate of chro- 

 mium remains. Nitric acid when warm, dissolves it, and 

 forms with it a brown solution ; the acid may be dissipated 

 by exposure to a temperature sufficient to volatilize it ; the 

 oxide remains unchanged. Sulphuric acid dissolves it, and 

 when the solution is heated, it becomes a protosulphate. It 

 may be obtained, by evaporating a solution of chromate of 

 chromium to dryness on a vapor bath ; it then presents the 

 above characters. It however contains water, which may be 

 expelled by an increased temperature, but the oxide is ren- 

 dered insoluble. When heated, in a retort connected with 



Vol. XIV.— No. 1. 18 



