262 CHEMICAL TESTS AND ANALYSES 



use in the determination of the specific gravity of milk highly ad- 

 vantageous and satisfactory. 



TOTAL SOLIDS 



BY MEANS OF THE BABCOCK FORMULA. For rapid and reason- 

 ably accurate work the total solids of milk may be determined by 

 the use of the Babcock formula, which is as follows : 



Total solids = -^ f- 1.2 X f. 



L = Quevenne lactometer reading, 

 f = per cent of fat. 



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

 Total solids = ?j- + 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 percentage of nitro- 

 gen 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 distilla- 

 tion the- flasks are fitted with rubber stopper^ and bulb tubes, as 

 given under distillation flasks. 



