THE ACTIVITIES OF THE ORGANISM 91 



hydrogen explodes when brought in contact with 

 platinum black, and a mixture of coal gas and air 

 inflames, a reaction which is made use of in the little 

 gas-lighting apparatus which most people have seen. 

 If, again, a powerful electric current be passed between 

 platinum wires which are a little distance apart, and 

 are immersed in water, the metal becomes torn away 

 from the points of the wire in the form of an impalpable 

 powder, colloidal platinum. The liquid containing 

 this colloid then has the power of setting up chemical 

 changes in other substances, changes which would 

 not otherwise occur, or, at least, would occur very 

 slowly. 



In general such catalysts, platinum black or 

 colloidal platinum for instance, have the following 

 characters : (i) a small quantity is sufficient to cause 

 change in a large (theoretically an infinite) quantity 

 of the substance acted upon ; (2) the nature and 

 quantity of the catalyst remain at the end the same, 

 as at the beginning of the reaction ; (3) a catalyst does 

 not start a reaction in any other substance or sub- 

 stances, it can only influence the rate at which this 

 reaction may occur : apparently it does, in some 

 cases, start a reaction, but in such cases we suppose 

 that the latter proceeds so slowly as to be imper- 

 ceptible ; (4) the final state of the reaction is not 

 affected by the catalyst ; it depends only on the nature 

 of the interacting substance or substances ; (5) the 

 final state is not affected either by the nature or 

 quantity of the catalyst : it is the same if we employ 

 different catalysts, or a large or small quantity of the 

 same catalyst. Finally, it appears that the phenomena 

 of catalysis are universal : " There is probably no kind 

 of chemical reaction," says Ostwald, ' which cannot 

 be influenced catalytically, and there is no substance, 



