4()fj PHILOSOPHICAL TRANSACTIONS. [ANNO J 784. 



It remains to consider in what manner these acids act in producing dephlogis- 

 ticated air. The way in which the nitrous acid acts, in the production of it 

 from red precipitate, seems to be as follows. On distilling the mixture of quick- 

 silver and spirit of nitre, the acid comes over, loaded with phlogiston, in the 

 form of nitrous vapour, and continues to do so till the remaining matter acquires 

 its full red colour, by which time all the nitrous acid is driven over, but some of 

 the watery part still remains behind, and adheres strongly to the quicksilver; so 

 that the red precipitate may be considered, either as quicksilver deprived of part 

 of its phlogiston, and united to a certain portion of water, or as quicksilver 

 united to dephlogisticated air ;* after which, on further increasing the heat, the 

 water in it rises deprived of its phlogiston, that is, in the form of dephlogisti- 

 cated air, and at the same time the quicksilver distils over in its metallic form. 

 It is justly remarked by Dr. Priestley, that the solution of quicksilver does not 

 begin to yield dephlogisticated air till it acquires its red colour. Mercurius 

 calcinatus appears to be only quicksilver which has absorbed dephlogisticated air 

 from the atmosphere during its preparation ; accordingly, by giving it a sufficient 

 heat, the dephlogisticated air is driven off, and the quicksilver acquires its 

 original from. It seems therefore that mercurius calcinatus and red precipitate, 

 though prepared in a different manner, are very nearly the same thing. 



From what has been said it follows, that red precipitate and mercurius calci- 

 natus contain as much phlogiston as the quicksilver they are prepared from ; but 

 yet, as uniting dephlogisticated air to a metal comes to the same thing as 

 depriving it of part of its phlogiston and adding water to it, the quicksilver may 

 still be considered as deprived of its phlogiston ; but the imperfect metals seem 

 not only to absorb dephlogisticated air during their calcination, but also to be 

 really deprived of part of their phlogiston, as they do not acquire their metallic 

 form by driving off the dephlogisticated air. 



In procuring dephlogisticated air from nitre, the acid acts in a different man- 

 ner, as on heating the nitre red-hot, the dephlogisticated air rises mixed with a 

 little nitrous acid, and at the same time the acid remaining in the nitre becomes 

 very much phlogisticated ; which shows that the acid absorbs phlogiston from the 

 water in the nitre, and becomes phlogisticated, while the water is thereby turned 

 into dephlogisticated air. On distilling 3155 grs. of nitre in an unglazed earthen 



* Unless we were much better acquainted than we are with the manner in which different sub- 

 stances are united together in compound bodies, it would be ridiculous to say, that it is the quick- 

 silver in the red precipitate which is deprived of its phlogiston, and not the water, or that it is the 

 water and not the quicksilver ; all that we can say is, that red precipitate consists of quicksilver and 

 water, one or both of which are deprived of part of their phlogiston. In like manner, during the 

 preparation of the red precipitate, it is certain that the acid absorbs phlogiston, either from the 

 quicksilver or the water; but we are by no means authorized to say from which. — Orig. 



