the compounds of chromium. 161 
well for converting chromium into an oxide ; I therefore had 
recourse to alkalies. 3*14 grains of metallic chromium in 
powder, were mixed with a sufficient quantity of hydrate of 
potash and nitre, in the proportion of about 5 parts of the 
former to one part of the latter, and kept for 20 minutes in a 
red heat in a silver crucible by means of a spirit lamp. The 
water of the hydrate gradually went off, and a reddish yellow 
matter remained, which was quite liquid while hot, but became 
solid on cooling. It dissolved completely in water, and the 
liquid had the usual yellow colour of a solution of chromate 
of potash. It was neutralized by nitric acid, and then pre- 
cipitated by acetate of lead. The chromate of lead thrown 
down, after being washed and dried upon the filter, weighed 
i6 - 8 grains, but was reduced to 16-23 grains when exposed 
to a red heat over a spirit lamp. 
By this process the metallic chromium had been converted 
into chromic acid. Now chromate of lead is composed of 
1 atom chromic acid - - 6-5 
1 atom protoxide of lead - 14 
20-5 
From this constitution of the salt, it is easy to deduce the 
weight of chromic acid in 16-23 grains of chromate of lead : 
it amounts to 5*146 grains. 
Thus it appears that 3-14 grains of chromium, when con- 
verted into chromic acid, become 5*i46grains. This gives 
us 3-966 for the atomic weight of chromium. For 
5 ' 146 : 3’ 14 : : 6-5 (atom of chromic acid) : 3-966 = atom 
of chromium. 
My stock of metallic chromium being small, I did not 
MDCCCXXVII. Y 
