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and resisted aqua regia and spirit of salt. If the electricexplosion is made very strong, the glass commonly flies inpieces, with such force, that it is necessary for the operatorto have his face fkreened from them.

The preparation of gold which has been principallyrecommended for tinging glass is Caflius’s precipitate bysolution of tin. To obtain this precipitate of the duecolour, a good deal of care is necessary both in dissolvingthe tin, and in diluting the solutions. A mixture of twoparts of aqua fortis and one of spirit of salt is supposed tobe the best menstruum for the tin : into this mixturesome fine block tin, granulated, is to be let fall, grainby grain, waiting till one grain is dissolved before anotheris dr opt in, that the dissolution may go on slowly, with-out any heat or discharge of fumes. The gold is dis-solved in common aqua regia; and a few drops of thissolution being mixed with some ounces of pure water,as many drops of the solution of tin are added. If themixture changes immediately to a clear bright purplish redcolour, the due degree of dilution has been hit; if thecolour appears dull, a greater quantity of water must beadded for the rest of the solutions. After the mixture hasdeposited its red matter, and become clear, a little moreof the tin solution is to be dropt in, for discovering, andprecipitating, any gold that may still remain in it : theliquor being then poured off, the precipitate is washedand dried.

Kunckel mentions another purple gold-powder, madenearly like that of Neri already mentioned, by inspissatingsolution of gold to dryness, abstracting from it fresh aquaregia three or four times till the matter looks almost likeoil, then precipitating with strong alkaline ley, and wash-ing the precipitate with water. By dissolving this powder

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