— 306 — 



bereouer, who, following in the track of Saussure, on. 

 the absorbing power of porous substances, ascertained 

 that the powder of platinum is capable of condensing 

 within its pores 250 times its volume of oxygen, which 

 as the porfs do not exceed one fourth of the bulk of 

 powder, must occupy no more than lilOOOth of its bulk 

 as gas and must be clearer than water, this explains 

 the action of the sponge or powder of platinum on hy- 

 drogen, Avhich under ordinary circumstances repel each 

 other, be brought within the distance at which chemi- 

 cal attraction exerts its influence, combination occurs, 

 and water is formed. This power possessed by plati- 

 num of condensing so enormous a volume of oxygen 

 within its pores enables it to decompose or oxidise many 

 organic compounds. Alcohol or ether for example, 

 dropped on platinum black, are at once changed by oxi- 

 dation in acetic acid with so great a rise of tempera- 

 ture as to inflame the undecomposed alcohol or ether. 

 In like manner this powder when placed ia contact 

 with a solution of formic acid, at once converts it into 

 carbonic acid which escapes with copious effervescence. 

 Platinum is not, however, the only metal that exhibits 

 this property. Palladium, Rhodium and Iridium, pre- 

 pared in the same manner as Platiuum and spongy 

 Nickel, obtained by calcining oxalate of nickel in a re- 

 tort, possesses the same power of effecting the combi- 

 nation of oxygen with hydrogen at ordinary tempera- 

 tures. Gold, osmium, and several other metals in a 

 minute state of division, are iu like manner capable of 

 effecting the combination of these gases at slightly ele- 

 vated temperatures. — In the preceding paragraphs the 

 influence of surface or porosity in causing the combi- 

 nation of gases, and the decomposition and oxilation 

 of organic compounds, has been shown to exist in the 

 hightest degree in platinum and those metals that ap- 

 proach platinum most nearly in character, but it will 

 presently be seen that all porous substances possess the 

 same power in various degrees, according to the fine- 

 ness of their pores, until it is at length lost, or exerted 

 in so slow a manner as to become imperceptible. 



Charcoal stands next to platinum in the power of 

 coadensing gases within its pores, but in a far inferior 



