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4 So Third Appendix, mild foda, avoiding fufion, but the hardefl, as the precious ftones may be even melted with fix or eight times tbeir vveight of cauflic fixed alkali, and one or other of thefe operations lhould be repeated until the filiceous part of the fione, af- tei digefiion in aqua regia, and fubfequent tor- refadion, becomes white, and perfedly vitrifies with its own weight of fixed alkali, with effer- vefcence, or abfolutely refufes to do fo, and thus appears to be adamantine. 86. 1 he torrefied, or melted mafs, if whitilh, contains but little of any metal; if bluifh, pro- bably manganefe; if greenilb, manganefe and iron; it lhould then be well pulverized, thrown on a filtre, and treated with pure water, until the water comes off taftelefs. Many faturate the alkalized mafs immediately with nitrous or ma rine acid, inftead of water ; and often this is ad- vantageous and proper, as all the foluble earths are then in a greater fiate of divifion, and con- fequently more eafily foluble ; but it may alfo happen, that the fione contains the vitriolic acid, which, during • torrefadion, with the alkali, unites with this alkali, and alfo calx, or barytes, or magnefia; when the whole is afterwards dif- folved in the nitrous or marine acids, a double decompofition in this cafe takes place, and the felenite or barofelenite are re-produced. Hence the former method is in general the fafeft. 87. The alkaline folution ihould be duly eva- porated jf too aqueous, and faturated with ni trous acid, even to a fiight excefs ; the filiceous part of the fione will thus be precipitated frequently in a gelatinous form ; and, to halfen its precipi- tation, it lbould be heated to 180°, and gradu- ally evaporated to a confidcrable degrec; fome argill,