170 now oitoi'S 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 lieat, 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 poAver, so that, 

 for example, when it is brouglit 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 chloride 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, being able to take up or " occlude " 900 times its volume of the gas, 

 (.Graham, Proceedings Roy. Hoc., 1868^ p. 432.J 



