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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1878 Excerpt:...in order to remove the excess of nitric acid. This mass consists of impure picric acid, and treated with cold or hot water, it furnishes solutious which, when filtered, may bo employed for tho ordinary processes of dyeing. It is, however, preferable to purify the acid and to prepare it in the crystallised condition. For this purpose two processes may be employed. The yellow mass may be extracted by boiling water sufficiently acidulated with sulphuric acid to render comparatively insoluble the yellow resinous matters. (These yellow matters are produced by an incomplete transformation, partly of the phenol, but principally of the neutral oils, and other foreign matters accompanying it, and which havoalso been attacked by the nitric acid.) The picric acid crystallises from the solution (the more easily for being acidulated with sulphuric acid), and is doposited in the form of crystalline plates of a light yellow colour. But these crystallisations cause the loss of a considerable quantity of substance, and by no means eliminate completely the yellow tarry matter. It is therefore better to convert the impure acid into a salt which may be easily purified, and afterwards to precipitate the acid from it. The picrate of potassium is very applicable for this purification, as it is only slightly soluble in cold water, whilst it is readily soluble in boiling. But in operating upon a large scale, the filtration of large quantities of the salt becomes extremely difficult, as the liquids, even when boiling and contained in heated funnels, have a great tendency to crystallise on the filters, which then become choked. Several manufacturers therefore adopt another process, which consists in saturating a boiling solution of picric acid with carbonate of soda, excess being avo...