566 Dr. Prout on the ultimate composition 
of its operation ; but perhaps a few practical remarks on some 
of the circumstances to be attended to during its employment, 
may not be deemed superfluous. 
The substance to be analysed may be placed in a small 
tray made of platina foil, and introduced alone into the tube P, 
and gradually submitted to the action of heat and oxygen 
gas ; but this does not answer well with organic compounds, 
as a portion of them is apt to escape combustion. Another 
method is to mix the substance with pure silicious sand, and to 
retain the mixture in the centre of the tube by means of 
asbestos. But this method often fails, except there be about an 
inch of the oxide of copper at each end of the tube, which 
must be kept red hot during the experiment, and in this case it 
succeeds completely with many substances. Another method, 
and that which the most generally succeeds, is to mix the 
substance with peroxide of copper, to heat these together 
in the tube in the first place, and afterwards to open the 
other stop-cock and send the oxygen gas through the ignited 
and partially reduced oxide, by means of which it again 
becomes peroxidized ; and any portion of the substance that 
had escaped complete combustion in the first part of the 
experiment, is now completely burnt. This last method is 
also that employed when it is required to determine the 
quantity of carbonic acid gas yielded by a given quantity 
of any substance ; only in this case, of course, oxygen gas is 
not required, and the contents of the tube P, must be taken 
out and well triturated, and subjected to heat a second time. 
If it should be required to analyse the gas formed, one 
method of removing it from the tube I, is represented at 
Fig. 5 ; and others will readily occur to the practical chemist. 
The following are some of the advantages of this appa~ 
