344 CHEMICAL TESTS AND ANALYSES 



L = Quevenne lactometer reading, 

 f =. per cent of fat. 

 Example : Lactometer reading is 32 ; per cent fat is 4. 



Total solids = --+ 1.2 X 4 = 12.8 per cent. 



Gravimetric Method. "Heat from three to five grams of 

 milk at the temperature of boiling water until it ceases to lose 

 weight, using a tared flat dish of not less than 5 c.c. diameter. If 

 desired, from fifteen to twenty grams of pure, dry sand may be 

 previously placed in the dish. Cool in a desiccator and weigh rapid- 

 ly to avoid absorption of hygroscopic moisture." 



Ash. 



"Weigh about twenty grams of milk in a weighed dish, add 

 6 c.c. of nitric acid, evaporate to dryness and ignite at a tempera- 

 ture just below redness until the ash is free from carbon." 



Total Nitrogen. 



Place about five grams of milk in a Kjeldahl digestion flask 

 and proceed, without evaporation, as described under "Gunning 

 Method" for the determination of nitrogen. Multiply the percent- 

 age of nitrogen by 6.38 to obtain nitrogen compounds. 



Gunning Method. 

 Apparatus. 



(a) Kjeldahl flasks for both digestion and distillation. 

 These are flasks having a total capacity of about 550 c.c., made of 

 hard, moderately thick and well-annealed glass. When used for 

 distillation the flasks are fitted with rubber stoppers and bulb tubes, 

 as given under distillation flasks. 



(b) Kjeldahl digestion flasks. These are pear-shape, round- 

 bottomed flasks, made of hard, moderately thick, well-annealed 

 glass, having a total capacity of about 250 c.c. They are 22 c.m. 

 long and have a maximum diameter of 6 c.m., tapering gradually to 

 a long neck, which is 2 c.m. in -diameter at the narrowest part and' 

 flared a little at the edge. 



(c) Distillation flasks. For distillation a flask of ordinary 

 shape, of about 550 c.c. capacity may be used. It is fitted with a 



