183 
J. 
■ X 
the compounds of chromium. 
Green oxide - - 5*13 or 5*183 or 5*89 
Oxygen - - - i‘S03 or 1*317 or 1*5 
6*500 7*39 
This makes the atomic weight of green oxide 5*183, instead 
of 5; and if we consider 1*5 as the excess of oxygen in 
chromic acid over green oxide, we have the atomic weight 
of chromic acid 7*39, instead of 6*5, which is the true 
number. \ 
The experiment was repeated twice, but without coming 
nearer the truth. I shall briefly mention the results of these 
two experiments. 
10 grains of anhydrous green oxide were boiled in a silver 
crucible with a strong potash ley till water ceased to be 
driven off. The whole was then heated to redness, and kept 
in that state for a quarter of an hour. The dry mass being 
digested in water and filtered, there remained on the filter a 
blackish matter, which, dried on the sand bath, weighed o*66 
grain. When heated it glowed, and the weight was reduced 
to 0*33 grain. Thus 9*66 grains of green oxide had been 
converted into chromic acid. The potash solution treated as 
before gave 41*492 grains of chromate of lead, equivalent to 
13’156 grains of chromic acid. Consequently, chromic acid 
is composed of 
Protoxide 9*66 or 4*145 or 4*775 
Oxygen - 3*496 or 1*5 or 1*727 
13*156 5*645 6*5 
12*99 grains of anhydrous green oxide were mixed with a 
great excess of bicarbonate of potash which had been tritu¬ 
rated with a little nitre. This mixture was slowly raised to 
