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TESTING. 91 and set on fire. The boracie acid, if present, is volatilized with the alcohol, and imparts a decided green colour to the flame. Carbon in powder heated with nitre deflagrates.—Carbonic acid cannot be detected in the dry way. It is easily discovered by the effervescence which is produced when the assay is treated with hydrochloric acid, heated if necessary. The gas evolved is void of smell. Carbonic acid in solution, on adding lime water or barytes water, yields a precipitate, which effervesces witli acids. Silicic acid alone remains unchanged, is very slowly dissolved in borax, and very slightly in phosphoric salt; in soda, how'- ever, it melts with violent effervescence into a clear glass. There are two modifications of silicic acid; one of which, the amorphous, is soluble in water and acids, the other, the crystal line, is acted on only by hydrofluoric acid. The former is rea dily soluble in boiling solution of potash, the latter with great difficulty. Many silicates can be dissolved in hydrochloric acid, the more readily the stronger the base, the smaller the quantity of silicic acid, aud the greater that of water contained in them. The hydrocliloric acid either combines with the base, leaving the silica as a jelly or powder, or it dissolves the silica also, which does not gelatinize till the solution is evaporated. But many of the silicates are insoluble in acids, and must be rendered soluble by fusion with carbonate of soda, during which the silica combines with the soda. On evaporating the solution a jelly is formed, and then a dry residue, partly soluble in boiling hydrochloric acid; the remainder is silica. Alcalis and Earths. Ammonia is discovered immediately by its smell, when the assay is heated in the closed tube with soda. When an am- moniaeal salt iB rubbed together with hydrate of lime, or warmed with a solution of potash, the ammonia is also driven off, and is known either by its smell or by its browning turmeric paper, or by the white cloud which is formed when a glass rod, moistened with hydrochloric acid, is held over the assay. Soda is discovered in a mineral by the reddish yellow colour which it imparts to the outer flame w hen the assay is strongly heated. Soda yields a precipitate with antimoniate of potash ; it gives no precipitate with chloride of platinum or with sul phate of alumina; and with tartaric acid a fine acicular pre cipitate, only when the solution is very much concentrated. Cithia, when its quantity is not too small, is discovered by the beautiful carmine red which the assay imparts to the flame while in fusion. When the proportion of lithia is small, the same colouring is exhibited, according to Turner, on melting