To make up the batch of lithopone the solution containing the original 1050 pounds of barium sulphide and 856 pounds of titanium acid cake is added to sufiicient zinc sulphate solution of approximately 35 Baum at 60 Centigrade to completely precipitate all the BaS as zinc sulphide and barium sulphate so that the final precipitate contains a suspen-. sion of co-p'recipitated zinc sulphide barium sulphate intimately mixed with a suspension of titanium oxide. On the completion of the reaction, shown by the complete absence of either soluble zinc or barium in a filtered por-.

WILLIAM J. OBRIEN.

Should a grade of lithopone be desired higher than the standard grade and another by-productas, for example, a forty-five*per= cent. grade of lithopone and barium chlorid the following process may be pi'acticed,\vhich, however, is quite analogous to the one already 10o described. Aqueous solutions of the ingredients are prepared as before, in these proportions: zinc sulfate, one hundred and sixty-one pounds; zinc chlorid, one hundred and thirty-six pounds, and barium sulfid, three hundred and thirty-eight pounds. Upon mixing these several solutions the lithopone will at once be precipitated in accordance with the following reaction: