18 



2. For practical purposes, by the use of an areometer (lacto- 

 deiisimeter). 



Weighing in a flash : The flask used for the determination 

 of the specitic gravity is of thin glass, and is closed with a care- 

 fully ground, solid glass stopper, or one consisting of a thermometer. 

 The latter are, for convenience sake, to be preferred. This flask 

 should hold from 30 c.c. to 50 c.c, and the edge «>f its neck should 

 not be laid outward and rounded, but cut off straight.' To clean 

 these flasks after use, they should be rinsed with caustic soda solu- 

 tion, then with water and absolute alcohol, and finally with ether. 

 Cloth should be used, instead of paper, to dry and clean them ex- 

 ternally. 



It must be avoided to touch the flask with the hands while it is 

 used, to prevent changes to temperature, which, by the consequent 

 expansion of the fluid, would lead to inaccurate results. The tem- 

 perature of fluids, the specific gravity of which is thus to be de- 

 termined, should not vary more than 2° from the temperature of 

 the air in the balance-room. Should it be warmei', it would hap- 

 pen, especially in the case of milk, that the fluid at the sides be- 

 comes colder and commences to contract, while in the interior, 

 around the mercury bulb of the thermometer, the fluid retains its 

 original temperature. It is necessary, therefore, to determine the 

 temperature of the room by another thermometer. The tempera- 

 ture exerts a considerable influence upon the results. Therefore, 

 to obtain exact readings, the bulb of the thermometer should remain 

 in the fluid for at least one or two minutes, and then be read to 

 0.1 degree. The specific gravity found is corrected by the use 

 of Kopp's tables. 



VOLUMINA AND SPECIFIC GRAVITY OF "WatEE, ACCORDING TO 



