278 Dr. Henry on the action of finely divided platinum on 
•with the smallest proportion of hydrogen ; olefiant gas requir- 
ing more hydrogen, and carburetted hydrogen a still larger 
proportion. It is extremely probable, then, that the tem- 
perature, produced by the union of the hydrogen and oxygen 
forming part of any mixture, is the circumstance which de- 
termines the combustible gases to unite, or not, with oxygen 
by means of the sponge. It was desirable, however, to ascer- 
tain the exact temperature at which each of those three gases 
unites with oxygen with the intervention of the spongy plati- 
num. For this purpose the gases, mixed with oxygen enough 
to saturate them, were severally exposed in small retorts 
containing a platinum sponge, and immersed in a mercurial 
bath, to a temperature which was gradually raised till the 
gases began to act on each other. In this way the following 
facts were determined. 
1st. Carbonic oxide began to be converted into carbonic 
acid at a temperature between 300° and 310° Fahrenheit. 
By raising the temperature to 340°, and keeping it at that 
point for 10 or 15 minutes, the whole of the gas w r as acidi- 
fied, the condensation of volume in the mixture being equi- 
valent to the oxygen which had disappeared. 
edly. Olefiant gas, mixed with sufficient oxygen, and in 
contact with the sponge, showed a commencement of decom- 
position at 480° Fahrenheit, and was slowly but entirely 
changed into carbonic acid by a temperature not exceeding 
520° Fahrenheit. M M. Dulong and Thenard* state the 
same change to take place at 300° cent.= 572 0 Fahrenheit ; 
but having repeated the experiment several times, I find no 
reason to deviate from the temperature which I have as- 
signed. 
* Ann. de Chim. et de Phys. XXIII. 443. 
