On some Compounds of Chrome. 129 
That with tin is green; with manganese chesnut-brown. They 
have all very similar properties: they dissolve in acids, and are 
precipitable from them without decomposition; the chlorate and 
nitrate of potash change them into alkaline chromates, and me- 
tallic oxides. - I have tried, but without success, several methods 
of separating them by analysis. With chlorate of potash they 
undergo a combustion similar to that of nitre and cream of tar- 
tar, A solublechromate is indeed obtained, but the oxides of 
iron, of manganese, or of tin, retain much of the chromic oxide. 
Muriate of chrome renders muriate of manganese very soluble in 
alcohol; caustic alkalies cannot separate the whole of the oxide 
of tin from the oxide of chrome. These compounds deserve a 
fuller examination. 
Chromaie of Lead. 
It.is well known that a reddish chromate of lead is obtained 
by precipitating acetite of lead with an alkaline chromate of 
potash ; but if the sub-acetite of lead and neutral chromate are 
used, both boiling hot, a yellow precipitate falls down, which in a 
few moments passés into a most brilliant orange-red. This tint 
may be heightened by boiling a little alkali with the red, or even 
with the yellow chromate of lead. I have made a comparative 
analysis of the yellow and the red artificial chromate, and the 
native red lead of [Siberia All of them give exactly the same 
proportion between the acid and the oxide. ‘They are neutral 
chromates, only the red chromate coutains a small quantity of 
alkali, apparently from 1 to 14 per cent. The method which 
I used in these analyses was to dissolve the chromate in muriatic 
acid, which in a boiling heat became muriate of chrome; then 
to precipitate the lead by sulphuretted hydrogen, the oxide of 
chrome by ammonia; and lastly, to evaporate to obtain the mu- 
riate of potash. All the alkalies will change the fine yellow of 
the chromate of lead, and also of bismuth, into red. 
It remains to inquire whether the alkali is combined with the 
chromic acid, the oxide of lead, or the chromate of lead. For 
this purpose, I treated a very pure chromate of lead and bismuth 
in excess with a small quantity of alkali, assisting the action by 
heat. After some instants the liquid had ceased to redden tur- 
meric, and had assumed a yellow tint. Sometimes the tur- 
meric test showed the absence of free alkali before the liquid 
changed colour, at which time the chromate contained free oxide 
of lead. Indeed, if a little litharge is added to the chromate 
along with the alkali, it will become red without losing chromic 
acid, One may even obtain red chromate by boiling together 
chromate of potash and litharge. 
It follows from these facts that the alkali appears to be com~- 
Vol, 59, No. 286. Feb. 1822, R bined 
