1825.3 finely divided Platinum on Gaseous Mixtures. 425 



mixed with oxygen sufficient to saturate only one of them, were 

 exposed in a glass tube to the flame of a spirit lamp, without 

 the presence of the sponge, till the tube began to soften, the 

 combination of the gases was effected without explosion, and 

 was merely indicated by a diminution of volume, and an oscil- 

 latory motion of the mercury in the tube. At the close of the 

 experiment, out of twenty volumes of oxygen, eight were found 

 to have united with the carbonic oxide, and twelve with the 

 hydrogen, proportions which do not materially differ from the 

 results of the first experiment in the foregoing table. At high 

 temperature, then, the attraction of hydrogen for oxygen appears 

 to exceed that of carbonic oxide for oxygen ; at lower tempera- 

 tures, especially when the gases are in contact with the platinum 

 sponge, the reverse takes place, and the affinity of carbonic 

 oxide for oxygen prevails. 



Extending the comparison to the attraction of olefiant and 

 hydrogen gases for oxygen at a red heat, I found that when 

 six volumes of olefiant, six of hydrogen, and three of oxygen 

 were heated by a spirit lamp till the tube softened, a silent com- 

 bination took place as before ; all the oxygen was consumed ; 

 but only half a volume had been expended in forming carbonic 

 acid, which indicates the decomposition of only one quarter of 

 a volume of olefiant gas. On attempting a similar comparison 

 between carbonic oxide and olefiant gas, by heating them with 

 oxygen in the same proportions, the mixture exploded as soon 

 as the glass became red hot, and burst the tube. 



The property inherent in certain gases, of retarding the action 

 of the platinum sponge, when they are added to an explosive 

 mixture of oxygen and hydrogen, is most remarkable in those 

 which possess the strongest attraction for oxygen ; and it is 

 probably to the degree of this attraction, rather than to any 

 agency arising out of their relations to caloric, that we are to 

 ascribe the various powers which the gases manifest in this 

 respect. This will appear from the following table, the first 

 column of which shows the number of volumes of each gas 

 required to render one volume of an explosive mixture of hydro- 

 gen and oxygen uninflammable by the dischargeof aLeyden jar; 

 while the second column shows the number of volumes of each 

 gas necessary, in some cases, to render one volume of an explo- 

 sive mixture insensible to the action of the sponge, and in other 

 cases indicates the number which may be added without pre- 

 venting immediate combination. In the first column, the num- 

 bers marked with an asterisk were determined by Sir Humphry 

 Davy ; the remaining numbers in that column, and the whole of 

 the second, are derived from my own experiments. 



