36 2 Dr. Prout on the ultimate composition 
the matter in despair, and endeavour to contrive some other 
mode of analysis that should be free from these difficulties 
altogether. After a good deal of consideration I was induced 
to adopt a method which had occurred to me long before, 
but which I had never put in execution. This method is very 
simple, and founded on the following well known principles. 
When an organic product containing three elements, hy- 
drogen, carbon, and oxygen, is burnt in oxygen gas, one of 
three things must happen, i. The original bulk of the 
oxygen gas may remain the same, in which case the hydrogen 
and oxygen in the substance must exist in it in the same proportions 
in which they exist in water ; ( for it is well known that oxygen 
gas by being converted into carbonic acid gas is not altered in 
its bulk) : or, 2. The original bulk of the oxygen may be 
increased , in which case the oxygen must exist in the substance 
in a greater proportion than it exists in water; or, 3. The 
original bulk of the oxygen gas may be diminished, in which 
case the hydrogen must predominate. 
Hence it is obvious, that in the first of these cases the com- 
position of a substance may be determined by simply ascer- 
taining the quantity of carbonic acid gas yielded by a known 
quantity of it; while in the other two, the same can be readily 
ascertained by means of the same data, and by noting the 
excess or diminution of the original bulk of the oxygen gas 
employed. Such are the simple and universally admitted 
amount of -03 gr. though often much less than this. I was a good deal puzzled to 
account for this anomaly at first, but believe that it arose chiefly from the reoxy- 
dation of the partially reduced oxide, by the air of the atmosphere. 
Since this Paper was read before the Royal Society, I have observed one or two 
other singular facts connected with this subject, which will be noticed when we 
come to speak of the analysis of substances containing azote. 
