Dr. Percival had tried, without effect, to dissolve lead in water impregnated with fixed air. I however thought it probable, that the experiment might succeed with nitrous air. Into a quantity of water impregnated with it, I put several pieces of sheet-lead, and suffered them, after agitation, to continue immersed about two hours. A few drops of vol. tincture of sulphur changed the water to a deep orange colour, but not so deep as when the same tincture was added to a glass of the same water, into which one drop of a solution of sugar of lead had been instilled. The precipitates of both in the morning, were exactly of the same kind; and the water in which the lead had been infused all night, being again tried by the same test, gave signs of a still stronger saturnine impregnation--Whether the nitrous air acts as an acid on the lead, or in the same manner that fixed air dissolves iron, I do not pretend to determine. Syrup of violets added to the nitrous water became of a pale red, but on standing about an hour, grew of a turbid brown cast. Though the nitrous acid is not often found, except produced by art, yet as there is a probability that nitre may be formed in the earth in large towns, and indeed fossile nitre has been actually found in such situations, it should be an additional caution against the use of leaden pumps. I tried to dissolve mercury by the same means, but without success. I am, with the most sincere esteem, Dear Sir, Your obliged and obedient servant, THO. HENRY. _FINIS._ FOOTNOTES: [15] See Dr. Falconer's very useful and ingenious treatise on the Bath water, 2d edit. p. 313. [16] May, 1772. [17] Vid. Mr. White's useful treatise on the management of pregnant and lying-in women, p. 279. [18] See the author's observations on the efficacy of external applications in the ulcerous sore throats, Essays medical and experimental, Vol. I. 2d edit. p. 377. [19] The author of these observations. [20] Directions for impregnating water with fixed air, in order to communicate to it the peculiar spirit and virtues of Pyrmont water, and other mineral waters of a similar nature. [21] Referring to the case communicated by Mr. Hey. [22] He languished about a week, and then died. [23] The vegetables which are most efficacious in the cure of the scurvy, possess some degree of a stimulating power. [24] This refers, to an experiment mentioned in the first publication of these papers in the Philosophical Transactions, but omitted in this volume.