AN ACID TEST OF CREAM. 259 



inch thick, and they can be used instead of the one-tenth 

 normal alkaline liquid and the liquid indicator already men- 

 tioned. The tablets can be used for testing the acidity of 

 cream in the following way: 



Dissolving the tablets. — A 50 c. c. glass cylinder, grad- 

 uated, and on a foot, is found to be a convenient piece of ap- 

 paratus to use in preparing the solution of the tablets. It is 

 made of stout glass, not easily broken, and can be obtained 

 of any dealer in chemical apparatus. Put five tablets into • 

 this cylinder, add hot or cold soft water until the cylinder is 

 filled up to the 50 mark, then cork the cylinder and shake 

 frequently until the tablets all disappear in solution. If the 

 solution of the tablets is hastened by shaking the bottle or 

 stirring the liquid it should be done in such a way as to pre- 

 vent any loss. As they do not dissolve immediately they 

 should be put to soak about one-half hour before the cream 

 is to be tested. The strength of the solution does not change 

 perceptibly by standing four or five hours, but there is some 

 change in a tablet solution which is a day or more old. The 

 solid tablet will not change, and the only precaution neces- 

 sary is to use a fresh solution of the tablets in testing the 

 acidity of the cream. Excepting the flocculent residue or 

 settlings, which will not dissolve in water, the tablets should 

 all disappear in the solution before it is added to the cream 

 to be tested. When the solution is complete the cylinder 

 contains a reddish-colored liquid, the alkaline strength of 

 which is indicated by the number of tablets which were put 

 into the cylinder. 



Testing the cream. — The cream to be tested should be 

 thoroughly mixed. Then measure 25 c. c. of the cream into 

 a glass tumbler or a cup. If the cream is very thick 25 o. c. 

 of clean rain water may be mixed with it in the dish. The 

 sourness of the cream is then ascertained by adding the red- 

 dish-colored solution of the tablets to this measured quantity 

 of cream until it retains a pinkish color. When the two 

 liquids, cream and tablet solution, are thoroughly mixed the 

 pink color does not remain permanent until the acid of the 

 cream is completely neutralized by the alkali of the tablets. 

 An excess of the alkali causes the color to increase. The 



