gaseous mixtures , and its application to their analysis. 277 
accomplished, when the platinum ball has occasioned a dimi- 
nution of the mixture, at about the same rate as atmospheric 
air is diminished by nitrous gas, when the former is admitted 
to the latter in a narrow tube. 
SECTION II. 
ON THE EFFECT OF FINELY DIVIDED PLATINUM ON GASEOUS 
MIXTURES AT INCREASED TEMPERATURES. 
The effect of varying the proportion of free hydrogen to 
the compound combustible gases, on the degree of action 
which is excited by the platinum sponge, will perhaps admit 
of being explained, by examining the facts that have been 
stated, in connection with the degrees of combustibility of the 
compound gases under ordinary circumstances. The precise 
degree of temperature at which any one of them burns is 
not known, on account of the imperfection of our present 
methods of measuring high degrees of heat. It has been 
ascertained, however, by Sir Humphry Davy,* that at a heat 
between that of boiling mercury, and that which renders 
glass luminous in the dark, hydrogen and oxygen gases 
unite silently, and without any light being evolved ; that 
carbonic oxide is as inflammable as hydrogen ; that olefiant 
gas is fired by iron and charcoal heated to redness ; but that 
carburetted hydrogen, to be inflamed, requires that the wire 
should be white hot. Now this is precisely the order in 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 
* On Flame, 8vo. p. 72. 
