56() PHILOSOPHICAL TRANSACTIONS. [ANNO 1784. 



mixtures than from others, hut continued in all of them till the substances were 

 reduced to dryness. I found, in the receiving water &c. very nearly the whole 

 of the nitrous acid used for their solution, but highly phlogisticated, so as to 

 emit nitrous air by the application of heat ; and there is reason to believe, that 

 with more precaution the whole might have been obtained. 



8. As the quantity of dephlogisticated air produced by these processes did not 

 form a sufficient part of the whole weight, to enable me to judge whether any 

 of the real acid entered into the composition of the air obtained, I ceased to 

 pursue them further, having learned from them the fact, that however much the 

 acid and the earths were dephlogisticated before the solution, the acid always be- 

 came highly phlogisticated in the process. In order to examine whether this 

 phlogiston was furnished by the earths, some dephlogisticated nitrous acid was 

 distilled from minium till no more acid or air came over. More of the same acid 

 was added to the minium as soon as it was cold, and the distillation repeated, 

 which produced the same appearance of red fumes and dephlogisticated air. 

 This operation was repeated a third time on the same minium, without any sen- 

 sible variation in the phenomena. The process should have been still further re- 

 peated, but the retort broke about the end of the 3d distillation. The quantity 

 of minium used was 120 grs. and the quantity of nitrous acid added each time 

 was 240 grs. of such strength that it could dissolve half its weight of mercury, 

 by means of heat. 



It appears from this experiment, that unless minium be supposed to consist 

 principally of phlogiston, the source of the phlogiston, thus obtained, was 

 either the nitrous acid itself, or the water with which it was diluted ; or else that 

 it came through the retort with the light, for the retort was in this case red-hot 

 before any air was produced ; yet this latter conclusion does not appear very 

 satisfactory, when it is considered, that in the process wherein the earth made 

 use of was magnesia, the retort was not red-hot, or very obscurely so, in any 

 part of the process ; and by no means luminous when -the yellow and red fumes 

 first made their appearance. 



9. As the principal point in view was to determine whether any part of the 

 acid entered into the composition of the air, I resolved to employ some substance 

 which would part with the acid in a moderate heat, and also give larger quanti- 

 ties of air than had been obtained in the former processes. Mercury was thought 

 a proper substance for this purpose. 240 grs. of mercury were put into a glass 

 retort, with 480 grs. of diluted dephlogisticated nitrous acid, which was the 

 quantity necessary to dissolve the whole of the mercury ; a gentle heat was ap- 

 plied, and as soon as the common air contained in the retort was dissipated, a 

 vessel w;is placed to receive the nitrous air proceeding from the solution, which 

 v\as lOoz. measures. When it had ceased to give nitrous air, the neck of the 



