188 Dr. Thomson on some of 
the oxide assumed a fine green colour. The loss of weight 
was 0-18 grain. 
12 grains of the brown oxide in its original state, as pre¬ 
pared, were put into a green glass tube, shut at one end and 
bent into a retort-like form, as before described. The open 
end of the tube rose to the top of a small glass jar, standing 
over mercury, and containing 3 cubic inches of air. Heat 
was applied to the oxide in the tube by means of a small 
charcoal fire. No gas was extricated till the oxide became 
red hot. At that temperature 1*169 cubic inch of oxygen 
gas came over. The heat was raised as high as the tube could 
bear, and it was continued till the evolution of gas had been 
for some time over, and till the oxide had assumed a fine 
green colour. During this process the oxide did not glow. 
The weight of 1*169 cubic inch of oxygen gas is 0*4009 
grain. 
From a preceding experiment it is evident, that 12 grains 
of the brown oxide employed, when exposed to a strong red 
heat, were reduced to 9*36 grains ; or, the loss of weight was 
2*64 grains. From the experiment just stated, it appears 
that 0*4009 gr. of that weight is oxygen. Consequently, the 
constituents of the brown oxide may be represented as follows; 
Green oxide - - 9*36 
Oxygen _ - - 0*4009 
Water - - _ 2*2391 
12*0000 
But the oxygen must have been combined with green oxide, 
so as to constitute chromic acid. We may therefore repre¬ 
sent the constitution of brown oxide of chromium in the 
following manner. 
