Testing the Acidity of Milk and Cream. 117 



and laid on its side, as the tablets will dissolve more 

 quickly when the cylinder is placed in this position than 

 when left upright with the tablets at the bottom. Several 

 cylinders containing the tablet solution may be prepared 

 at a time; as soon as one is emptied, tablets and water 

 are again added, and the cylinder is corked and placed 

 in a horizontal position. In this way fresh solutions 

 ready for testing are always at hand. The cylinder is 

 kept tightly corked while the tablets are dissolving, so 

 that none of the liquid is lost by the shaking. It is well 

 to put the tablets in the cylinder with water at night; 

 the solution will then be ready for use in the morning. 

 Excepting a flocculent residue of inert matter, " set- 

 tlings," which will not dissolve, the tablets must all dis- 

 appear in the solution before this is used. The strength 

 of the tablet solution does not change perceptibly by 

 standing for twenty-four hours; but a change takes place 

 in solutions older than this. The solid tablets will not 

 change if kept dry any more than dry salt changes by age. 

 The only precaution necessary is to use a fresh solution 

 when acidity tests are made. 



138. Accuracy of the tablets. The tablets have been 

 repeatedly tested by competent persons and found to be 

 accurate and very uniform in composition. Tests made 

 with the tablets according to the directions here given 

 can be relied on as correct. The alkali solution is very 

 sensitive however and should not be measured in a cylin- 

 der which has been previously used for measuring sulfu- 

 ric acid as the smallest drop or film of acid from a dish 

 or from the operator's fingers will change the standard 

 strength of the tablet solution. The tablets must be com- 



