titanium oxide and 2 per cent' sulphuric acidand 63 per cent water, are slowly added to a solution containing 1050 pounds of barium sulphide, held in a large cylindrical tank, provided with a rotary agitation :capable of producing rapid agitation. The mass isthus v rapidly agitated, and the 2 per cent of sulphuric acid contained in the titanium acid cake reacts with a small portion of the barium sulphide. This reaction may be represented by the following equation TiO H 80 The free sulphuric acid of the titanium acid cake is neutralized by thebarium sul-' phide solution, forming barium sulphate and hydrogen sulphide, as indicated by the above equation. As the sulphuric acid is present only in a small percentage, the major porltiion of the barium sulphide remains as suc very fine colloidal suspension. The barium sulphate produced is also very fine, and the presence of this. very fine barium sulphate in suspension, and also of the very fine colloidal titanium oxide, is believed to be the explanation of the great improvement in the properties of the finished lithopone.
After settling, the clear solution containing the titanium oxide, is run oil andfurther processed, whereby a roduct is obtained containing approximate y 35 per cent titanium oxide, 2 per cent sulphuric acid and 63 per cent of water. This product is known in the trade as titanium acid cake. It is a plastic mags having somewhat the consistency of mu 1 ljha've discovered that lithopone can be greatly improved by the suitable use of this titanium acid cake, and that the results obtained are dependent to a large extent upon the methods'by which this titanium acid cake is used,'in the production of lithopone.