206 Testing Milk and Its Products. 



then found by dividing the weight of the milk by that of 

 the water. 



Example: Weight of sp. gr. bottle-}- water... 146.91 13 grams. 

 Weight of sp. gr. bottle empty 46.9423 " 



Weight of water .............. 99.9690 grams. 



Weightofsp.gr. bottle+milk ..... 149.8708 grams. 



Weight of sp. gr. bottle empty ..... 46.9423 " 



Weight of milk ........... ,...102.9285 grams. 



1O9 



Sp.gr. of milk=--=1.0296 



248. If a plain picnometer without a thermometer attached, 

 is available, the method of procedure is similar to that described, 

 with the difference that the temperature of the water and of 

 the milk must be brought to 60 F. before the picnometer is 

 filled, or the picnometer filled with either liquid is placed in 

 water in a small beaker, which is very slowly warmed to 60 F. 

 and kept at this temperature for some time so as to allow the 

 liquid in the picnometer to reach the temerature desired; the 

 temperature of the water in the beaker is ascertained by means 

 of an accurate chemical thermometer. The perforated stopper 

 is then wiped off, the picnometer is taken out of the water, 

 wiped and weighed. It is necessary to weigh very quickly if 

 the room temperature is much above 60 F., as in such cases the 

 expanding liquid will flow on to the balance pan, with a re- 

 sultant loss in weight from evaporation. 



The weights of specific-gravity bottle or picnometer, empty 

 and filled with water, need only be determined a couple of 

 times, and the averages of these weighings are used in subse- 

 quent determinations. 



249. Westphal balance. Where only a small amount 

 of milk is available, or in rapid work, the specific grav- 

 ity may be taken with considerable accuracy by means 

 of a Westphal balance. The arrangement and use of 



