218 Testing Milk and Its Products. 



For the determination of the specific gravity of lop- 

 pered milk, see 263. 



251. b. Water. The milk is weighed into a perfor- 

 ated copper tube filled with prepared dry asbestos. The 

 tubes are made from perforated sheet copper, with holes 

 about .7 mm. in diameter and about .7 mm. apart ; they 

 are 60 mm. long, 20 mm. in diameter and closed at the 

 bottom. The asbestos is prepared from clean fibrous 

 asbestos, which is ignited at low heat in a muffle oven, 

 treated with a little dilute HC1 (1:3) and then with 

 distilled water till all acid is washed out; it is then 

 torn in loose layers and dried at a low temperature in 

 an air bath ; when dry it can be easily shredded in fine 

 strings and is placed in a wide-mouth, glass-stoppered 

 bottle. 



About two grams of asbestos are placed in each tube, 

 packing it rather loosely; the tube is then weighed, a 

 small narrow beaker being inverted over it on the scale 

 pan. 5 cc. of milk are now dropped on to the asbestos 

 from a 5 cc. fixed pipette, the beaker again placed over 

 the tube, and the weight of the 5 cc. of milk delivered 

 +copper tube taken. The weight of the milk is ob- 

 tained by difference. The tubes are then placed in a 

 steam oven and heated at 100 C. until they no longer 

 decrease in weight, which ordinarily will take about 

 three hours. Place in a desiccator until cold, and weigh ; 

 the difference between the weight of the tube-fmilk and 

 this last weight gives the water contained in the milk, 

 which is then calculated in per cent, of the quantity of 

 milk weighed out. 



