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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-.

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I will now describe some typical methods of practicing my invention, whereby lithopone of any desired grade may be produced. One of the known grades of lithopone as prepared and mixed for the trade contains sev- 6o enteen per cent. of zinc sullid. To produce this grade and a by-product of hydrosulfid of sodium, for example, I proceed as follows: The usual precautions, it will be understood, mustbe taken in preparing or for insuring the purity of the several ingredients used; but these preliminaries do not require description here. Separate aqueous solutions of the following ingredients in the proportions named are prepared: zinc sulfate, one x hundred and sixty-one pounds; barium sulfid, three hundred and thirty-eight pounds, and sodium bisulfate one hundred and twenty pounds. These ingredients, it will be recognized, are readily soluble in water. The separate solutions are then mixed and the following chemical reaction at once takes place:

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