VOL. LXXJV.] PHILOSOPHICAL TRANSACTIONS. 55Q 



oz. measures of dephlogisticated air ; and he found that, on weighing the retort 

 and nitre before and after the process, they had suffered a loss of weight equal to 

 the weight of the air, and to the water of crystallization of the nitre, but 

 nothing more. He remarked that the air had a pungent smell, which he could 

 not divest it of by washing ; and that the water in which the air was received 

 had become slightly acid. I examined a portion of this water, and found by it 

 that the whole of the receiving water had contained the acid belonging to '2 

 drams = 120 grs. of nitre. I also examined the residuum, and the retort in 

 which the distillation had been performed, and found the residuum highly alka- 

 line, yet containing a minute quantity of phlogisticated nitrous acid. It had 

 acted considerably on the retort, and had dissolved a part of it, which was de- 

 posited in the form of a brownish powder, when the saline part was dissolved in 

 water. This earthy powder I have not yet thoroughly examined, but have no 

 doubt that it principally consists of the earth of the retort. This experiment, 

 and all others tried in earthen vessels, leave us still at a loss to determine what 

 becomes of the acid and phlogiston. They seem either to remain mixed with 

 the air, in the form of an incoercible gas ; or to unite with the alkali, or with 

 the earth of the retort, in some manner so as not to be easily separated from 

 them ; or else they are imbibed by the retorts themselves, which are sufficiently 

 porous to admit of such a supposition. All that appears to be conclusive from 

 this experiment is, that above one half of the weight of the nitre was obtained 

 in the form of dephlogisticated air ; and that the residuum still contained some 

 nitrous acid united to phlogiston. 



7. Finding that the action of the nitre on the retort tended to prevent any 

 accurate examination of the products, I had recourse to combinations of the 

 nitrous acid with earths from which the dephlogisticated air is obtained with less 

 heat than from nitre itself. As these processes have been particularly described 

 by Dr. Priestley, by Mr. Scheele, and others, I shall not enter into any detail of 

 them ; but shall mention the general phenomena which I observed, and which 

 relate to the present subject. The earths I used were magnesia alba, calcareous 

 earth, and minium or the red calx of lead. I dissolved them in the respective 

 experiments in nitrous acid dephlogisticated by boiling, and diluted with proper 

 proportions of water. I made use of glass retorts, coated with clay ; and I re- 

 ceived the air in glass vessels, whose mouths were immersed in a glazed earthen 

 bason, containing the smallest quantity of water that could be used for the pur- 

 pose. As soon as the retort was heated a little above the heat of boiling water, 

 the solutions began to distil watery vapours containing nitrous acid. Soon after 

 these vapours ceased, yellow fumes, and in some of the cases dark red fumes, 

 began to appear in the neck of the retort ; and at the same time there was a pro- 

 duction of dephlogisticated air, which was greater in quantity from some of these 



