OXYGEN AND THE NATURE OF AC ID 8. 129 



In the case of other substances mere exposure to the air, aided by a 

 moderate degree of heat, suffices to bring about the combination, and 

 this is what happens to all vegetable substances capable of passing on to 

 acid fermentation. In the greater number of cases one has to resort to 

 the science of affinities and to employ the acidifying principle already 

 united in another compound. 



The example which I am going to give to-day is of this last sort, and 

 I shall take it from an experiment, well known for several years, follow- 

 ing the memoirs of M. Bergman. It is the formation of the acid of 

 sugar. This acid, in accordance with the experiments which I am going 

 to recount, seems to me to be nothing else than sugar combined with 

 the acidifying principle or oxygen, and I propose to show in order in 

 different memoirs that we can combine this same principle with the 

 substance composing animals' horns, with silk, with animal lymph, with 

 wax, with essential oils, with extracted oils, manna, starch, arsenic, iron 

 and probably with a great many other substances of the three kingdoms. 

 "We can thus turn all these substances into genuine acids. 



Before entering on the material to be presented, I beg the Academy 

 to recall that the acid of nitre, as shown by the experiments which I 

 have before described, and which I have repeated in your presence, is 

 the result of the union of nitrous air with the purest air or acidifying 

 principle; that the proportion of these two principles varies in the differ- 

 ent kinds of acid of nitre, the one which gives off fumes, for instance, 

 containing a superabundance of nitrous air. 



vol. Lvni.— 9 



