CHKMICAI, TSSTS AND ANALYSES 265 



(b) AivBUMiN. Exactly neutralize with caustic alkali the fil- 

 trate obtained in the preceding operation (a), add 0.3 c.c. of a 10 

 per cent solution of acetic acid and heat the liquid to the tempera- 

 ture of boiling water until the albumin is completely precipitated, 

 collect the precipitate on a filter, wash and determine the nitrogen 

 therein. Nitrogen multiplied by 6.38 equals albumin," or 



To the filtrate of the casein determination add 0.3 c.c. of 10 per 

 cent acetic acid, boil until the albumin is completely precipitated and 

 proceed as directed in previous paragraph. 



In the place of the above methods the per cent of albumin may 

 be determined by subtracting the per cent of casein from the per 

 cent of total nitrogen. 



MILK SUGAR (LACTOSE) 



OPTICAL METHOD 

 PREPARATION OF REAGENTS 



"(a) Acid mercuric nitrate. Dissolve mercury in double its 

 weight of nitric acid, specific gravity 1.42, and dilute with an equal 

 volume of water. One cubic centimeter of this reagent is sufficient 

 for the quantities of milk mentioned below. Larger quantities may 

 be used without affecting the results of polarization. 



(b) Mercuric iodid with acetic acid. Mix 33.2 grams of po- 

 tassium iodid, 13.5 grams of mercuric chlorid, 20 c.c. of glacial 

 acetic acid and 640 c.c. of water." 



Determine the specific gravity of the milk by means of a delicate 

 hydrometer, or, if preferred, a pycnometer. The quantity of sam- 

 ple to be taken for the determination varies with the specific gravity 

 and is to be measured at the same temperature at which the specific 

 gravity is taken. The volume to be measured is indicated in the fol- 

 lowing table, which is based upon twice the normal weight of lactose 

 (32.9 grams per 100 metric c.c.) for the Ventzke sugar scale. 



Place the quantity of milk indicated in the table in a flask 

 graduated at 102.6 c.c., add 1 c.c. of the acid mercuric nitrate solu- 

 tion or 30 c.c. of the mercuric iodid solution (an excess of these rea- 

 gents does no harm), fill to the mark, shake, filter through a dry 

 filter and polarize. It is not necessary to heat before polarizing. If 

 a 200 m.m. tube is used, divide the polariscope reading by 2 (or, if a 

 400 m.m. tube is used, by 4) to obtain the per cent of lactose in the 

 sample. 



