CHAP. _3d. Of the nature of the nitro-aereal and fiery spirit._ Fire he conceives to consist of these nitro-aereal particles set in violent motion by means of sulphureous bodies, in the cases of culinary fire: but by some other means, in the cases of the solar rays collected by a burning glass, and of the celestial fires. The corrosive and caustic nature both of fire and nitrous acid, seems to argue that it proceeds in both from the nitro-aereal particles they contain, 22-24. That fire is not of a sulphureous nature is evident, for nitre will not take fire in an ignited crucible; but oil thrown in, takes fire immediately. So if a piece of metal be held over a candle, the fire particles pass through the metal, but the sulphureous smoke adheres to the under side. p. 27. That the heat occasioned by a burning glass, consists of these nitro-aereal particles is evident, for diaphoretic antimony may be made, either first by calcination with a lens, or secondly, by the repeated affusion of nitrous acid, or thirdly, by the deflagration of nitre on the antimony. Diaphoretic antimony made by calcination, increases on weight,[44] by means of the nitro-aereal particles fixed in it by the process. p. 28, 29. [44] It was first observed by John Rey in 1630 that metals calcined, gain weight by the absorption of air. See an account of his book by M. Bayen Journ. de Rozier 1775 v. 1 p. 48. There are also some experiments by Boyle that shew the accession of weight on the calcination of metals, but he does not seem aware of the theory. Shaw’s Boyle, Fire and Flame weighed v. 2 p. 394, &c.