STUDIES ON THE PHENOMENA OF CONTACT. 407 



It may be asked why tlie spongy platina acts more efSciently in phe- 

 nomena of contact than the wire of the same metal. It is because in proportion 

 as a body is divided its surftice is increased, and we have before seen that in 

 the gas battery the action is so much the more intense as there is a greater 

 surface of the phitina in contact with the gas. Hence it is that we have in 

 chemistry the general law, that the greater the division of bodies the better they 

 react. Now, platina sponge is platina extremely divided, that is to say, pre- 

 senting a very large surface. We further see the effect of division in the 

 inflammation of pyrophorus. 



In the phenomena which we have been examining the presence of ?i fourth 

 body usually prevents the phenomenon of polarity from taking place, and con- 

 sequently destroys the influence of the third body. Thus the presence of 

 carbonic acid, for example, in the case of oxygen and hydrogen, prevents their 

 combining through the presence of a metal. It is thus, too, that a drop of 

 essence, will prevent fermentation. The spongy platina condenses in its pores 

 from thirty to forty times its volume of ammoniacal gas. Now, in this state, it is 

 altogether unfit to effect the combination of oxygen and hydrogen, and the 

 platina does not recover this property so long as it contains ammonia. The 

 presence of a fourth body does not, however, always exercise this influence. It 

 is necessary that it should be a body suited to react with the others to place them 

 in a state of equilibrium. Thus the presence of a little nitrogen does not prevent 

 the combination or the slow combustion of hydrogen mixed with oxygen, under 

 the circumstances we are considering. It has been seen, from my experiments 

 cited above, that the presence of an acid (as a fourth body) prevents the produc- 

 tion of ozone in certain special cases. 



In ordinary fermentation, namely, in that, which is occasioned in a solution 

 of sugar by leaven, it has been shown by Gay Lussac that the presence or the 

 contact of air or of oxygen is an essential condition of the manifestation of the 

 phenomenon, but that a single particle of oxygen suffices to excite, by 

 leavening, the fermentation of a great quantity of sugar. Noav, we have already 

 seen that organic bodies may act upon oxj^gcn to transform it into ozone ; that 

 is, may induce a phenomenon of polarity ; and, moreover, in the experiments of 

 De Saussure, that organic bodies may cause the combination of hydrogen and 

 oxygen. We have already said that, in our opinion, fermentation commences 

 with a phenomenon of polarity ; oxygen or the leaven (it matters not which, as 

 action is always equal to reaction,) acts here as the platina does in the mixture 

 of oxygen and hydrogen. Polarity once brought into play in the saccharine 

 solution, there is no reason why it should cease as long as there remains any 

 sugar. The facility with Avhich oxygen, as we have seen, is transformed into 

 ozone by its contact with ftrganic bodies, determines, from the very first, this 

 phenomenon of polarity. The ozone produced being negative and the leaven 

 positive, in relation to the gas, this oxygen tends to combine Avith the leaven ; 

 the sugar is, as it were, placed between the two poles of a pile ; it is therefore 

 divided into two other bodies, of which one is negative (COo) and the other 

 positive (AEH.) 



Fig. 5. The presence of a fourth body often 



prevents this phenomenon; thus, when 

 the alcohol produced becomes suffi- 

 ciently predominant, all action ceases, 

 and it is necessary constantly to re- 

 move this product, if we wish the fer- 

 ^--''' ""'^'.^^ mentation to continue for an indefinite 



" %^ --^_ time. 

 — w It is probable that something anal- 



,^ T^cty^f^ ogous takes place when caseine con- 



verts sugar of milk into lactic acid. 



.^ 



+ 



^x^y. 



