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Barofeknite. 137 melted by pure air it gradually diffipates.—Mine ral alkali melts it with effervefcence, borax and microcofmic falt with fcarce any-, the firft decom- pofes it, the two laft extraft no colour frpm it. It does not form a plafter, as gypfums do ; yet Gerhard denies this. It contains about 84 per ct. of barytes, the re- mainder vitriolic acid and water, per Bergman. But artificial barofelenite contains 67 of earth and 33 of vitnolic acid and water, per Klaproth 2. Chyrn. An 1785.219. or 65 of earth and 35 of acid and water, per Fourcroy 4 Chem. An. 65. And Dr. Withering’s experiments appear to me to prove, that 100 parts marmor metallicum con- tain 68,5 pure earth and 31,5 acid, as ftrong as thatcontaincdin tartar vitriolate. See Phil. Tranf. 1784, 304. According to Dr. Withering’s own calculation, 100 parts of this ftone contain 67,2 of pure barytes, and 32,8 of vitriolic acid, whicli agrees almoft exaftly with Klaproth’s determina- tion. Barofelenite is frequently contaminated with felenite, filex, iron, and aerated calx, and hence fometimes flightly efTervefces with acids. To analyze and purify it, Mr. Afswelius ufes the following procefles: lft. Afterpulverization, it is mixed and cal- ^cined with 2,5 times its weight of aerated mineral alkali, perfcctly pure and deprived of its water of cryftallization, in a red heat for one hour and an half, avoiding fufion. A double decompofition thus takes place. 2d. Glauber’s falt and the fuperfluous alkali be- ing thcn feparated by lotion and coftion, *Ae re- 'liduum is boiled for 3 hours iw 10 times its weight of diltilled vinegar, wholefp. gr. is 1,033, ^ h,s takes