produced by Catalytic Bodies. 207 



the suboxide being in a state of solution, because the soluble 

 salts of the suboxide do not oxidize with such extraordinary 

 ease, nor is it to be expected that they should, if we admit that 

 the acid itself plays the part of oxygen. The accessory affi- 

 nity of alkalies for oxygen is exhibited in many other cases of 

 chemical action. Thus, colouring matters, such as deoxidized 

 logwood, Brazil-wood, peach-wood, japan, fustic and catechu 

 are oxidized more rapidly in contact with alkalies than in 

 water alone ; and various dyeing principles, such as orcine and 

 erythrine, absorb oxygen with great avidity in the presence of 

 ammonia. Sugar may be boiled with potash without de- 

 composition, but when air is admitted, formic, melassic, and 

 glucic acids are produced. Hydruret of benzyle when ex- 

 posed to air gradually absorbs oxygen and passes into benzoic 

 acid, but in contact with potash this absorption is very much 

 accelerated. The rapid decomposition of the gallates and of 

 hematine in the presence of free alkali and air is aphaenome- 

 non of the same kind. In fact, numberless instances of this 

 catalytic action of the alkalies are known to chemists. 



We find the influence of an accessory oxidation in many 

 cases of chemical union. Thus Campbell has shown * that 

 the transformation of cyanide of potassium into cyanate of 

 potash is much accelerated by the presence of the iron in yellow 

 prussiate of potash, the iron being converted into oxide during 

 the transformation. Here the iron plays the part of the 

 protoxide of manganese in the cases of oxidation already re- 

 ferred to, or it perhaps bears a more direct relation to the 

 action of lead in communicating a tendency to the base metals 

 to seize oxygen during the process of cupellation. The in- 

 fluence exerted by peroxide of manganese in first converting 

 cyanide of potassium into cyanate of potash and afterwards 

 into the carbonate of that base, is another instance of accessory 

 affinity ; for only a portion of the oxygen is derived from the 

 oxide employed. The solution of an alloy of silver and pla- 

 tinum in nitric acid may be supposed to be a similar affinity. 

 It is not necessary to believe that this is a case proving the 

 communication of intestine motion to the atoms of platinum, 

 by which it acquires the power of decomposing nitric acid f ; 

 for an equally simple explanation is given by assuming that 

 the united affinities of platinum and silver are able to decom- 

 pose nitric acid, both these affinities acting in one direction 

 at the same time, and enabling the platinum to dissolve. We 

 have only to suppose that the atoms of nitric acid are placed 

 by the silver in a state of such tension that the platinum can 



* Phil. Mag. Third Series, vol. xix. p. 513. 



t Liebig's Elements of Agriculture, 4th edit., p. 280. 



