40,000 x .0064 = 256 lbs. alkali. Since sulfate of alumina neutralizes one-third of its weight in caustic, and there are say 9 lbs. of this added per thousand pounds of lye we would add 40,000 x 9 = 360 lbs. of sulfate of alumina. This would neutralize 360 x 1/3 = 120 lbs of alkali. There are then 256 - 120 = 136 lbs. of alkali still to be neutralized. If 60deg. B. sulfuric acid is used it requires about 1.54 lbs. of acid to one pound of caustic. Therefore to neutralize the caustic soda remaining it requires: 136 x 1.54 = 209.44 lbs. 60deg. B. sulfuric acid to neutralize the total alkali in the 40,000 pounds of spent lye. The acid is added and the lye well stirred, after which another sample is taken and again titrated as before. From this titration the amount of acid to be added is again calculated and more acid is added if necessary. Should too much acid have been added, caustic soda solution is added until the lye is between exactly neutral and 0.02% alkaline. The filtered lyes at this stage have a slight yellowish cast. To be sure that the lyes are treated correctly the precipitation test is advisable. To carry this out filter about 50 c. c. of the treated lye and divide into two portions in a test tube. To one portion add ammonia drop by drop. If a cloudiness develops upon shaking, more alkali is added to the lye in the tank. To the other portion add a few drops of 1 to 5 sulfuric acid and shake the test tube. If a precipitate develops or the solution clouds, more acid is needed. When the lyes are treated right no cloudiness should develop either upon adding ammonia or the dilute acid. The properly treated lye is then run through the filter press while slightly warm and the filtered lye is fed to the evaporator from the filtered lye tank. The lye coming from the filter press should be clear and have a slight yellowish cast. As the pressure increases it is necessary to clean the press or some of the press cake will pass through the cloths. Where sodium silicate is used as a filler, the silicate scrap should never be returned to the soap kettle until the glycerine lyes have been withdrawn. This practice of some soapmakers is to be strongly censured, as it causes decided difficulty in filtering the lye, since during the treatment of the lye, free silicic acid in colloidal form is produced by the decomposition of the sodium silicate by acid. This often prevents filtering the treated lye even at excess pressure and at its best retards the filtering. As to the filter press cake, this may be best thrown away in a small factory. Where, however, the output of glycerine is very large it pays to recover both the fatty acids and alumina in the press cakes.