ANALYTIC PROCESSES 9 



the inclosure of the air, and to allow sufficient 

 time for the escape of any bubbles that may be 

 present. Sp. gr. is tmderstood to be taken at 15.5°; 

 samples should be brought near to this. If at 

 a few degrees above or below, it will suffice to 

 make the determination at once and obtain the 

 correct figure by reference to the annexed table. 

 The sp. gr. of normal milk ranges between 

 1.027 and 1.035. The figure alone does not 

 indicate the character of the sample, but taken 

 in conjunction with the figiu-e for fat or for 

 total soUds, it is of value as a check on the 

 results furnished by other determinations. 



The simplest method of determining sp. gr. is 

 by the lactometer, a delicate and accurately gradu- 

 ated hydrometer. The instrument must be im- 

 mersed carefully so as not to wet the stem above 

 the point at which it will rest. Its accuracy 

 should be verified by immersion in distilled 

 water at 15.5° and milks of known sp. gr. 



More accurate determinations may be made 

 with a balance. A special form, the Westphal 

 balance, is adapted to the determination of 

 sp. gr. only, the weights being so arranged 

 that a simple enumeration of them gives the 

 gravity directly. The cheap forms of this in- 

 strument are not satisfactory, but some made 

 by German houses are excellent. The ordinary 



