53 Fußbility, I Heat.| Of Binary Proportion!. Magnesia and Silex. 50 magnefia 1 50 filex J ■4 'melt with great difficulty even in the heat of pure air. Mem. Par. 1787, p. 398, into a white enamel; but in inferior heats they are infufible in all pro portions by the experiments of Achard, Mem. Berl. 1780, 33, and Margr. 1778, 4, and 1 Bergm. 372. Argill and Silex. 50 argill 1 50 filex J 160 f barely hardened, but no fign \ of fufion, Mr. Lavoifier found a mixture of equa! parts quartz and argill vitrifiable by pure air. But this experiment is fufpicious, as the quartz he ufed was more fufible than pure cryftal, and confe- quently impure. In a porcelain heat Mr. Achard found them in- fufible in all proportions j and Bergm. 337. Iron highly calcined and Calcareous Earth. According to Mr. Achard’s expe* riments, they melt at leall into a porcelain mafs, in every propor- tion, not exceeding 4 parts ot the one to 1 of the other ; but thofe mixtures, in which the calces of iron exceed the calcareous earth, are by far the moft fufible. Iron fully calcincd and Magnesia. ^ f So magnefia "1 |_ io calx ir >n J 75 magnefia 1 25 calx of iron J . I 64 magnefia 1 \ 3 3 calx of iron J ISS f infufible, Achard, Meni. Berl. 1 1 779» S3- f remained a brownifii black -j powder. Mr. Achard had the (_lame refult. remained a brown mafs. jo mag-