the compounds of chromium. 181 
was made to pass through the tube till all action was at an 
end. The chromate underwent combustion, and water was 
evolved pretty copiously. The loss of weight was 4-6 grains. 
Now, the constituents of 42 grains of chromate of lead 
may be represented as follows: 
Lead. Oxygen. 
28*68 protoxide of lead composed of 26*63 + 2*05 
Green oxide. 
13*32 chromic acid composed of - 10*246 -f- 3'074 
Total oxygen - - - 5*124 
By the process the chromic acid was totally reduced to 
green oxide. Globules of metallic lead could be detected in 
the residual matter. But had the whole lead been reduced, 
the loss of weight would have amounted to 5*124 grains, 
instead of 4*6 grains. The difference is 0*524, which rather 
exceeds ^th of the oxygen in the protoxide of lead. 
The whole of the residual matter having been digested in 
nitric acid for about a week, was dissolved, and formed a 
very dark bluish green liquid, from which the lead was pre¬ 
cipitated by sulphate of soda, and the green oxide by car¬ 
bonate of ammonia. When this last precipitate was dried it 
had a blue colour; when heated to redness it did not glow, 
as green oxide usually does, but assumed a dirty green 
colour. The weight was 9*36 grains. There had remained 
undissolved of the original matter 3*46 grains. It had a 
brownish yellow colour, and was chromate of lead, probably 
reproduced during the action of the nitric acid on the green 
oxide. It was composed of 
Protoxide of lead - - 2*36 
Chromic acid - - - i*io 
