Note 738 — THE LIFE OF SAMUEL JOHNSON, LL.D. (continued 4)
Reading edition
'Sept. 22, 1783. The chymical philosophers have discovered a body (which I have forgotten, but will enquire) which, dissolved by an acid, emits a vapour lighter than the atmospherical air. This vapour is caught, among other means, by tying a bladder compressed upon the body in which the dissolution is performed; the vapour rising swells the bladder and fills it. Piozzi Letters, ii.310. The 'body' was iron-filings, the acid sulphuric acid, and the vapour nitrogen. The other 'new kinds of air' were the gases discovered by Priestley.