INDUCTIVE AFFINITY. 1I>7 



held together by a very slight affinity. It is not decomposed 

 by acids, but alkalies give its elements a tendency to separate, 

 slow effervescence occurring with the disengagement of oxygen, 

 and water being formed. Nor do soluble substances alone pro- 

 duce this effect; other organic and inorganic bodies, also, 

 such as manganese, silver, platinum, gold, fibrin, &c. which 

 are perfectly insoluble, exert a similar power. The decompo- 

 sition, in these instances, takes place by the mere presence 

 of the foreign body, and without the smallest quantity of it 

 entering into the new compound, for the most minute researches 

 have failed in discovering the slightest alteration in the foreign 

 body itself. The liquid persulphuret of hydrogen, arid a solu- 

 tion of the nitrosulphate of ammonia of Peloaze are decom- 

 posed in the same way, and by contact of nearly all the 

 substances which act upon peroxide of hydrogen. One 

 remarkable difference indeed is observable, namely that alkalies 

 impart stability to nitrosulphate of ammonia, while acids de- 

 compose it, or the reverse of what happens with both the pe- 

 roxide and persulphuret of hydrogen.* 



The phenomena referred to catalysis are of a recondite nature 

 and much in need of elucidation. The influence of platinum, 

 formerly noticed, in disposing hydrogen and oxygen to unite, 

 is probably connected with the catalytic power of the same 

 metal, but is at present equally inexplicable. It would be 

 unphilosophical to rest satisfied by referring such phenomena 

 to a force, of the existence of which we have no evidence. The 

 doctrine of catalysis must be viewed in no other light than 

 as a convenient fiction, by which we are enabled to class 

 together a number of decompositions not provided for in the 

 theory of chemical affinity as at present understood, but which, 

 it is to be expected, will receive their explanation from new 

 investigations. It is a provisional hypothesis, like the doctrine 

 of isomerisni, for which the occasion will cease as the science 

 advances. 



INDUCTIVE AFFINITY. 



When a plate of zinc is plunged into hydrochloric acid, a 

 chemical change of a simple nature ensues, the metal dissolves 

 combining with the chlorine of the acid and displacing its 

 hydrogen, the gas-bubbles of which form upon the zinc plate, 

 increase in size, detach themselves, and rise through the liquor 

 to its surface. The solution of zinc, when effected by its 



* Phil. Mag. 3rd Series, vol. 10, p. 489. 



