508 PHILOSOPHICAL TRANSACTIONS. [ANNO 1784. 



This is owing to 2 causes, 1st, because a large quantity of nitrous air is pro 

 duced, by the continued action of the concentrated nitrous acid newly formed ; 

 and, 2dly, because the fixed air, on whose absorption the diminution depends, 

 is absorbed by the mercurial salt, as may be inferred from the experiment in l 

 Lavoisier, p. 248. 



Of the diminution of common air by the electric spark. — Of all the instances 

 of the artificial production of fixed air, by the union of phlogiston with the de- 

 phlogisticated part of common air, there is none perhaps so convincing as that 

 exhibited by taking the electric spark through common air, over a solution of 

 litmus, or lime-water; for the common air is diminished i, the litmus reddened, 

 and the lime-water precipitated. Mr. Cavendish indeed attributes the redness of 

 the litmus to fixed air; but he thinks it proceeds from a decomposition of some 

 part of the vegetable juice, as all vegetable juices contain fixed air. Yet that 

 such a decomposition does not take place, I think may be inferred from the fol- 

 lowing reasons: first, if the electric spark be taken through phlogisticated or 

 inflammable air confined by litmus, no redness is produced, the air not being in 

 the least diminished; and, 2dly, if the litmus were decomposed, inflammable 

 air should be produced as well as fixed air; and then there should be an addition 

 of bulk, instead of a diminution; but what sets the origin of the fixed air from 

 the phlogistication of the common air beyond all doubt is, that if lime-water be 

 used instead of litmus, the diminution is the same, and the lime is precipitated. 

 Here Mr. Cavendish says, the fixed air proceeds either from some dirt in the 

 tube; a supposition which, being neither necessary nor probable, is not admis- 

 sible; or else from some combustible matter in the lime; but lime contains no 

 combustible matter, except perhaps phlogiston, which cannot produce fixed air 

 unless by uniting to the common air, according to my supposition; but it is much 

 more probable that the diminution does not arise from any phlogiston in the 

 lime, as it is exactly the same whether lime-water be used or not; and the lime 

 does not appear to be in the least altered, and in fact contains scarcely any 

 phlogiston. 



Of the diminution of common air, by the amalgamation of mercury and lead. 

 — I attributed this diminution to the phlogistication of the common air by the 

 process of amalgamation, and the consequent production and absorption of fixed 

 air. On this Mr. Cavendish observes, " that mercury, fouled by the addition 

 of lead or tin, deposits a powder which consists in great measure of the calx of 

 the metal; he found also, that some powder of this sort contained fixed air; 

 but it is not clear that this air was produced by the phlogistication of the air in 

 which the mercury was shaken, as the powder was not prepared on purpose, but 

 was formed from mercury fouled by having been used for various purposes, and 

 may therefore contain other impurities, besides the metallic calx." On this I 



