r) t 
170 HOW CROPS FEED. 
brought to the condition of sponge, a form it assumes 
when certain of its compounds (e. g. ammonia-chloride of 
platinum) are decomposed by heat, or to the more finely 
divided state of platinum black. The latter is capable of 
condensing from 100 to 250 times its volume of oxygen, 
according to its mode of preparation (its porosity ?); and 
for this reason it possesses intense oxidizing power, so that, 
for example, when it is brought into a mixture of oxygen 
and hydrogen, it causes them to unite explosively. A jet 
of hydrogen gas, allowed to play on platinum sponge, is 
almost instantly ignited—a fact taken advantage of in 
Dobereiner’s hydrogen lamp. 
The oxidizing powers of platinum are much more vig- 
orous than those of charcoal. Stenhouse has proposed 
the use of platinized charcoal (charcoal ignited after moist- 
ening with solution of chioride of platinum) as an escha- 
rotic and disinfectant for foul ulcers, and has shown that 
the foul air of sewers and vaults is rendered innocuous 
when filtered or breathed through a layer of this material.* 
Chemical Action a Result of the Porosity of the Soil. 
—From these significant facts it has been inferred that the 
soil by virtue of the extreme porosity of some of its ingre 
dients is the theater of chemical changes of the utmost 
importance, which could not transpire to any sensible ex- 
tent but for this high division of its particles and the vast 
surface they present. 
The soil absorbs putrid and other disagreeable effluvia, 
and undoubtedly oxidizes them like charcoal, though, per- 
haps, with less energy than the last named substance, as 
would be anticipated from its inferior porosity. Garments 
which have been rendered disgusting by the fetid secre- 
tions of the skunk, may be “sweetened,” i. e. deprived of 
* Platinum does not condense hydrogen gas; but the metal Palladium, which 
occurs associated with platinum, has a most astonishing absorptive power for 
hydrogen, heing able to take up or “‘ occlude” 900 times its volume of the gas, 
(Graham, Proceedings Roy. Soc., 1868, p. 422.} 
