361 
of simple alimentary substances , &c. 
every means that could be thought of, as likely to succeed, 
were tried, but without effect, and I was obliged to relinquish 
employment alone of that substance perfectly useless when great accuracy is re- 
quired. It has been objected to the lamp that the heat produced by it is not 
sufficient; but this is a mistake; at least I have never met v/ith any substance 
that resisted its action, provided the oxide of copper was well shaken up in the 
tube, or, if necessary, taken out of the tube and retriturated, and afterwards 
exposed to heat a second time, one or other of which ought to be done in all 
instances, whatever be the medium of heat employed ; for no ordinary heat will 
induce the oxide to part with its oxygen to a combustible substance at some 
distance off, and not immediately in contact with itself. A great heat is also 
attended with some disadvantages, and among others, that of causing the oxide to 
adhere together in hard and solid masses, which thus becomes more difficult to be 
removed from the tube, and much less adapted for future experiments. In general 
organized bodies are more difficult of combustion, and require more heat than 
crystallized ones. The lamp described in the text I have only recently employed, 
and it answers the purpose in all respects better than any I have yet seen. 
With respect to the sources of error above mentioned, it was found that zoo grs. 
of the oxide of copper, recently ignited, gained, after ten or fifteen minutes exposure 
to the air, a quantity varying from ’02 to "05 gr. one half of which, or even more, 
was acquired before it became cold ; that is to say before it had cooled down to 
loo°, considerably above which point it began to acquire weight. Of the increase 
of weight above mentioned, it was found that about -j, or -J, (for the proportion 
varied from causes that I could not discover) was due to the condensation of air, 
the rest was due to moisture. The oxide I employed was perfectly pure, and 
prepared by exposing metallic copper to heat. Dr. Ure states, (t that 100 grs. of 
the oxide prepared from the nitrate of copper exposed to a red heat merely till 
the vapours of nitric acid were expelled, absorbed in the ordinary state of the 
atmosphere from •! to • 2 gr. in the space of an hour or two, and about half that 
quantity in a very few minutes.” 
In determining the quantity of water formed by the oxide of copper in the usual 
manner, there is yet another difficulty to contend with, to which we have alluded 
above, and which we shall here briefly notice. It has been stated, that complete 
combustion seldom or never takes place during one exposure to heat, and that in 
many cases the oxide ought to be removed from the tube and retriturated. Now it 
was found, almost invariably, that during the second exposure to heat, the tube, 
instead of losing additional weight, actually became heavier, sometimes to the 
MDCCCXXVII. 3 A 
