Scheele did not obtain fluoric acid in a state of purity, put only _fluosilicic acid_; nor were chemists acquainted with the properties of fluoric acid till Gay-Lussac and Thenard published their Recherches Physico-chimiques, in 1811. 3. Scheele's experiments on _manganese_ were undertaken at the request of Bergman, and occupied him three years; they were published in the Memoirs of the Stockholm Academy, for 1774, and constitute the most memorable and important of all his essays, since they contain the discovery of two new bodies, which have since acted so conspicuous a part, both in promoting the progress of the science, and in improving the manufactures of Europe. These two substances are _chlorine_ and _barytes_, the first account of both of which occur in this paper. The ore of manganese employed in these experiments was the _black oxide_, or _deutoxide_, of manganese, as it is now called. Scheele's method of proceeding was to try the effect of all the different reagents on it. It dissolved in sulphurous and nitrous acids, and the solution was colourless. Dilute sulphuric acid did not act upon it, nor nitric acid; but concentrated sulphuric acid dissolved it by the assistance of heat. The solution of sulphate of manganese in water was colourless and crystallized in very oblique rhomboidal prisms, having a bitter taste. Muriatic acid effervesced with it, when assisted by heat, and the elastic fluid that passed off had a yellowish colour, and the smell of aqua regia. He collected quantities of this elastic fluid (_chlorine_) in bladders, and determined some of its most remarkable properties: it destroyed colours, and tinged the bladder yellow, as nitric acid does. This elastic fluid, in Scheele's opinion, was muriatic acid deprived of phlogiston. By phlogiston Scheele meant, in this place, hydrogen gas. He considered muriatic acid as a compound of chlorine and hydrogen. Now this is the very theory that was established by Davy in consequence of his own experiments and those of Gay-Lussac and Thenard. Scheele's mode of collecting chlorine gas in a bladder, did not enable him to determine its characters with so much precision as was afterwards done. But his accuracy was so great, that every thing which he stated respecting it was correct so far as it went.