458 
Dr. Ure on the ultimate analysis of 
gentlemen assigning about 43 parts in the hundred of car- 
bon, while the latter states the carbon at only 40.* 
The objects of the present paper are, first to indicate, and 
endeavour to remove several sources of fallacy attending the 
method with peroxide of copper; and next, to exhibit the 
results of its application to a considerable series of vegetable 
and animal compounds. 
Peroxide of copper, prepared by igniting the pure nitrate 
of this metal, is, like yellow oxide of lead, and many other 
metallic oxides, readily absorbent of a small portion of hu- 
midity from the air, the quantity of which depends, in some 
measure, on the length of time during which it has suffered 
ignition. If exposed to a red heat, merely till the vapours 
of nitric acid are expelled, 100 grains of the oxide will absorb, 
in the ordinary state of the atmosphere, from one- tenth to 
two-tenths of a grain of moisture in the space of an hour or 
two ; and about one half of the above quantity in a very few 
minutes. The French chemists, who have operated most 
with this agent, seem to be well aware of this circumstance, 
for they direct the peroxide to be used immediately after 
ignition, and to be triturated with the organic matter in a hot 
mortar of agate or glass. Yet this precaution will not entirely 
prevent the fallacy arising from the hygrometric action ; for 
I find that peroxide thus treated does absorb, during the long 
trituration essential to the process, a certain quantity of mois- 
ture, which, if not taken into account, will produce serious 
errors in the analytical results. It is better therefore to leave 
the powdered peroxide intended for research, exposed for 
such time to the air, as to bring it to hygrometric repose, 
* Dr. Prout has informed me, since the above paper was written, that he re-tri- 
turated and re-ignited the contents of his tubes, in the analysis of sugar. 
