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49 z , Third Appendix. folution, but they will affume a blue colour, froin the precipitation of the yellow calx, as aU ready explained. This lye alfo takes up the fulphur, coalj and, by the walhings, part of the tartar vitriolate and earth of alum contained in the Berlin blue, for w'hich reafon it will always precipitate barytic or ftronthian folutions vifibly, and thofe of calx, though perhaps invifibly, by reafon of ^he greater folubility of ftlenite, and hence it is a bad teil for metals. Baume endeavoured to remedy thefe defe&s, by adding diftilled vinegar until the lye ceafed to depofit a blue calx; but, as the aftion of this weak acid muft be exerted fome hours, and even days, before it can precipitate various gradations even of ihe yellow calx, it is impof- fible to detertnine its quantity with precilion ; if too little be added, the lye ftill continues defec- tive; and if too much, this, after many days, or perhaps weeks, will loofen the union of the blue calx, by expelling from the alkali that por- tion of the tinging matter neceflary to keep it in the ftate of a blue, and leaving it for a while only that which retains a yellow calx united to the alkali, and thus leaves it in a fhort time as imperfeft as at firft ; befides, the vitriolic con- taminations ftill remain. Mr. Bergman’s lye is the fame as that of Mac- quer; the proportions only being more accurately defined, for the purpofe of fubfequent corrcdion. His alkali is formed by the detonation of equal parts nitre and cream of tartar, and, confe- quently, nearly cauftic. This he dilfolves in about a pint of water, and digefts with four times its weight of Berlin blue, gradually added until it ceafes to be difcoloured, fupplying it with