126 POPULAR SCIENCE MONTHLY. 



It results from the experiments contained in this memoir that when 

 mercury is dissolved in nitric acid, this metallic substance acquires the 

 pure air contained in the nitric acid and constituting it an acid. On the 

 one hand this metal, when combined with the purest air, is reduced to 

 a calx; on the other the acid deprived of this same air expands and forms 

 nitrous air, and the proof that such are the facts in this experiment is 

 that if after having thus separated the two airs which enter into the 

 composition of the acid of nitre, you combine them anew, you make 

 pure acid of nitre such as you had before, with the single difference 

 that it fumes. 



The acid of nitre, drawn from saltpetre by clay, is consequently 

 nothing but nitrous air combined with nearly an equal volume of the 

 purest part of the air and with a fairly large amount of water; nitrous 

 air, on the contrary, is the acid of nitre deprived of air and of water. 

 People will no doubt ask here if the phlogiston of the metal does not 

 play some part in this process. Without daring to decide a question of 

 so great importance, I will reply that since the mercury comes out of 

 this experiment just as it went in, there are no signs that it has lost or 

 gained any phlogiston, unless we claim that the phlogiston which 

 brought about the reduction of the metal passed through the vessels. 

 But that is to admit of a particular sort of phlogiston, different from 

 that of Stahl and his school; it is to return to the theory of fire as a 

 principle, to fire as an element of bodies, a theory much older than 

 Stahl's and very different from it. 



I will end this memoir as I began it, by thanking M. Priestley, to 

 whom the greater part of whatever interest it possesses is due; but the 

 love of truth and the progress of knowledge, towards which all our 

 efforts should be directed, oblige me at the same time to correct a 

 mistake which he has made, which it would be dangerous to leave un- 

 challenged. This rightly famous physicist, who had discovered that 

 when he combined the acid of nitre with any earth, he invariably ob- 

 tained ordinary air or air better than ordinary air, believed that he 

 could thence draw the conclusion that the air of the atmosphere is a 

 compound of acid of nitre and of earth. This bold conception is quite 

 overthrown by the experiments contained in this memoir. It is clear 

 that it is not air that is composed of acid of nitre, as M. Priestley 

 claims; but, on the contrary, it is the acid of nitre that is composed of 

 air; and this single remark gives the key to a large number of experi- 

 ments contained in Sections III., IV. and V. of M. Priestley's second 

 volume. 



