474 PHILOSOPHICAL TRANSACTIONS. [anNO 1788. 



contains water, he found from the iron that is heated in it becoming a pro- 

 per finery cinder. At the publication of his last volume of experiments, he 

 had found, that iron heated in nitrous air acquired weight, and that what re- 

 mained of the air was phlogisticated air. Having since that time repeated this 

 experiment, and afterwards heated the iron, which was by this means increased 

 in weight, in inflammable air, the iron lost its additional weight, and water was 

 copiously produced, as in the same process with finery cinder, or, as he some- 

 times calls it, scale of iron. As nitrous air may be deprived of its water, and 

 become phlogisticated air by heating iron in it, he finds that it undergoes the 

 same change by being repeatedly transmitted through hot porous earthen tubes, 

 through which he had discovered that vapour will pass one way, while the air 

 contiguous to the heated tube will pass the other. 



That nitrous air contains water, and that this water can contribute to the 

 formation of fixed air, is evident from the following experiment. He heated 5 

 grains of charcoal of copper in 8 ounce-measures of nitrous air, till it was 

 increased to 10 ounce-measures, and the charcoal had lost 1 grain. Examining 

 the air, he found about l of it to be fixed air, and the remainder phlogisticated. 

 It seems therefore, that nitrous air consists of water, and something that may 

 be called the basis of nitrous acid, or that substance which, when united to 

 dephlogisticated air, will make nitrous acid; and this seems to be pure phlogiston, 

 since it is found, as the preceding experiments show, in the purest inflammable 

 air. May we not hence infer, that the nitrous is the simplest of all the acids, 

 and perhaps the basis of all the rest ? 



Mr. Watt desires it might be mentioned as his conjecture, that the nitrous 

 acid is contained in the inflammable air as the acid of vitriol is in sulphur, the 

 phosphoric in phosphorus, &c. ; and that the dephlogisticated air does nothing 

 more than develope the acid. Mr. Keir, who was led to expect that an acid 

 must be the result of the union of dephlogisticated and inflammable air, because 

 some acid is always the consequence of its union with other inflammable sub- 

 stances, thinks that both may be necessary ingredients in it. Further experi- 

 ments may throw more light on the subject. 



To the analysis of the above acid liquor, by Dr. Withering, he adds the fol- 

 lowing inferences : these. Sir, are all the trials I have made with the liquors pro- 

 duced in your experiment. They pretty clearly prove the acid generated to be 

 the same, whether the dephlogisticated air was procured from red precipitate of 

 mercury, from minium, or from manganese, and that this acid is the nitrous 

 acid. It is not quite so clear why the liquor and sediment in ^ 4 gave no stronger 

 marks of the presence of nitrous acid; but it is evident that the acid had united 

 itself to the iron, if not to the tin, of the vessel employed: and I find, that 

 when nitrous acid is fully saturated with iron by being boiled with it, and fixed 



