THE PASTEURIZATION OF MILK 



preferably methylene blue or uranin, is allowed 

 to flow into the tank with the heated water. The 

 time is observed between the time of its introduc- 

 tion and the time when the first trace of it appears 

 at the outlet. In order to make the test as ac- 

 curate as possible, care should be taken that a com- 

 plete solution is made of the color, otherwise small 

 particles of solid color may fall through the liquid 

 and deceive the observer. The solution of any 

 color is of course slightly heavier than the liquid 

 in which it is dissolved, and the tendency is for 

 it to fall after its introduction. Therefore, the 

 solution should be made as nearly as possible of 

 the same specific gravity as the water in the tank. 

 If it can be made slightly less in weight than the 

 water the result of the test will be rather better. 

 Even with the greatest care, it seldom happens that 

 two tests of the same apparatus will bring iden- 

 tical results. Unless the speed of flow is accu- 

 rately gauged, the results will differ. 



The temperature test is sometimes used to de- 

 termine the efficiency of these holders. When this 

 method of testing is employed it is the practice to 

 fill the holders with water in the same manner as 

 with the color test. The temperature of the water 

 116 



