96 



MODERN IMETHODS OF TESTING MILK 



FIG. 38 — FARRINGTON's 

 ALKALINE-TABLET TEST 



.034 gram of lactic acid. The apparatus (Fig. 38) 

 consists of a 17.6 cc. pipette, a white porcelain cup, and 

 a 100 cc. graduated glass cylinder provided with a 

 rubber stopper. 



Preparing the alkali solution. — In using the alka- 

 line tablets, one first puts 5 tablets into the graduated 



100 cc. cylinder, and fills 

 this to the 97 cc. mark with 

 clean, soft water, prefera- 

 bly distilled. The cylinder 

 is then tightly corked and 

 laid on its^ side until the 

 tablets dissolve, which re- 

 quires several hours. The 

 cylinder must be kept 

 tightly corked so that 

 none of the solution can be lost while the tablets are 

 dissolving. A slight flocculent residue will not dis- 

 solve, consisting of some inert matter used in the mak- 

 ing of the tablets. 



Precautions in using alkali solution. — The solu- 

 tion should always be shaken well before using. It 

 should always be kept tightly stoppered when not in 

 use. The solution, if kept perfectly stoppered, will 

 not greatly change in a week. Solutions older than 

 this may change their strength and should not be used. 

 It is a wise precaution to throw away solutions previ- 

 ously used for some days and to prepare a fresh solu- 

 tion. The solid tablets do not change if kept dry. 



Operation of alkaline-tablet test. — The material 

 (milk, cream, etc.) to be tested is thoroughly mixed, 



