On Vegetable and Animal Analysis . 49 
No. 12. 
Extract from a Memoir on Vegetable and Animal Ana- 
lysis. By M. M. Gay Lussac and Thenard.* 
When we had conceived the project of analysing ani- 
mal and vegetable matters, the first consideration which 
presented itself to onr serious attention was to trans- 
form, by means of oxygen, the vegetable and animal sub- 
stances into water, carbonic acid, and azote. It was evi- 
dent that if we could succeed in operating the transfor- 
mation so as to collect all the gases, this analysis would 
be accomplished with very great precision and simplici- 
ty. Two obstacles presented themselves : one was t© 
burn completely the hydrogen and the carbon of these 
substances, and the other to operate the combustion in 
close vessels. 
We could expect to surmount the first difficulty only 
by means of the metallic oxydes which easily give up 
their oxygen, or by the hyper- oxygenated muriate of pot- 
ash. Some experiments soon made us give the prefer- 
ence to the above salt, which succeeded beyond all ex- 
pectation. It was not quite so easy, however, to over- 
come the latter difficulty; for we could not attempt coim 
bustion in a retort full of mercury. To prevent the mat- 
ter from being burnt, the retort must have been broken : it 
became necessary to find an apparatus, therefore, in which 
we might— 
1. Burn portions of substance so small as not to frac- 
ture the vessels. 
2. To make a great number of successive combustions^ 
in order that the results might be perceptible. 
3. To collect the gases as they were formed. 
* Tilloch, vol. 38, p. 60. From Annales de Chimie, tome 74, p 47 
VOL. II. G 
