1825.] finely divided Platinum on Gaseous Mixtures. 423- 



but that carburetted hydrogen, to be inflamed, requires that the 

 wire should be white hot. Now this is precisely the order iti 

 which the three compound gases require hydrogen to be added 

 to them, in order to be rendered susceptible of being acted upon 

 by the platinum sponge ; carbonic oxide being acted upon with 

 the smallest proportion of hydrogen ; olefiant gas requiring more 

 hydrogen ; and carburetted hydrogen a still larger proportion. 



It is extremely probable, then, that the temperature, produced 

 by the union of the hydrogen and oxygen forming part of any 

 mixture, is the circumstance which determines the combustible 

 gases to unite, or not, with oxygen by means of the sponge. It 

 was desirable, however, to ascertain the exact temperature at 

 which each of those three gases unites with oxygen with the 

 intervention of the spongy platinum. For this purpose the 

 gases, mixed with oxygen enough to saturate them, were seve- 

 rally 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 was acidified, the condensation 

 of volume in the mixture being equivalent to the oxygen which 

 had disappeared. 



2dly. Olefiant gas, mixed with sufficient oxygen, and in con- 

 tact with the sponge, showed a commencemeni of decomposi- 

 tion at 480° Fahrenheit, and was slowly but entirely changed 

 into carbonic acid by a temperature not exceeding 520° Fahren- 

 heit. MM. Dulong and Thenard* state the same change to 

 take place at 300° cent. = 572° Fahrenheit ; but having 

 repeated the experiment several times, I find no reason to 

 deviate from the temperature which I have assigned. 



3rdly. Carburetted hydrogen, exposed under the same circum 

 stances, was not in the least acted upon by a temperature Ot 

 555° Fahrenheit, the highest to which, by an Argand's lamp, I 

 was able to raise the mercurial bath. This, however, must have 

 been near the temperature required for combination ; for on 

 removing the retort from the mercurial bath, and applying a 

 spirit lamp, at such a distance as not to make the retort red hot, 

 a diminution of volume commenced, and continued till all the 

 carburetted hydrogen was silently converted into water and 

 carbonic acid. 



4thly. Cyanogen, similarly treated, was not changed at a tem- 

 perature of 555° Fahr. and on applying the flame of a spirit lamp 

 to the tube, it produced no action till the tube began to soi'toi. 



• Ann. de Chim. et ile Phys. xxiii. 443. 



