Chemical Analysis of Milk and Its Products. 217 



weight of the empty bottle from the second and the 

 third weights, respectively, and the specific gravity of 

 the milk then found by dividing the weight of the milk 

 by that of the water. 



Example: Weight of sp. gr. bottle-f-water . . .146.9113 grams. 

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



Weight of water 99.9690 grams. 



Weight of sp. gr. bottle+milk 149.8708 grams. 



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



Weight of milk 102.9285 grams. 



Sp. gr. of milk=: 1 -|^r = 1.0296 



249. 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 temperature 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 resultant 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 subsequent de- 

 terminations. 



250. 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 

 this convenient little apparatus is readily explained 

 verbally. 



