PHYSICAL AND CHEMICAL EXAMINATION OF MILK 195 



2. Dissolve 178 grams of Rochelle salts and 50 grams of NaOH 

 in water and make up to 500 c.c. 



3. Mix equal volumes of Nos. 1 and 2 immediately before use. 

 Determination. — Mix 50 c.c. of the mixed copper reagent in a 



beaker and heat to the boiling-point. While boiling add 100 c.c. 

 of the milk solution and boil for six minutes. Filter immediately 

 through asbestos and determine the amount of copper reduced 

 by hydrogen or by an electrolytic process. Obtain the weight of 

 lactose equivalent to the weight of copper found from the table on 

 page 193. 



Leach prefers the method of O'Sullivan and Defren for the 

 gravimetric determination of lactose, and gives the following direc- 

 tions: "25 grams of the milk sample (24.2 c.c.) are transferred to 

 a 250-c.c. flask, 0.5 c.c. of a 30 per cent, solution of acetic acid are 

 added, and the contents well shaken. After standing for a few 

 minutes about 100 c.c. of boiling water are run in, the contents 

 again shaken, 25 c.c. of alimaina cream are next added, the flask 

 shaken once more, and set aside for at least ten minutes. The 

 supernatant liquid is then poured upon a previously moistened 

 ribbed filter, and finally the whole contents of the flask are brought 

 thereon, and the filtrate and washings made up to 250 c.c. The 

 filtrate must be perfectly clear. The milk-sugar in a solution thus 

 prepared would ordinarily not exceed 0.5 to 1 per cent. 



"Twenty-five c.c. of the milk-sugar solution are added to a hot 

 mixture of 15 c.c. each of Fehling's copper and alkali solution and 

 50 c.c. of water. The cupric oxid is filtered off and weighed. By 

 multiplying the weight with 0.6024 the amount of anhydrous milk- 

 sugar is obtained." For more accurate results the table on page 

 194 should be used. 



Volumetric Method. — " Twenty c.c. of raw milk are diluted 

 with water to a volume of 400 c.c. and a few drops of a 10 per cent, 

 solution of acetic acid added. The amount of acetic acid may vary 

 between 8 and 16 drops. After the precipitate has settled, it is 

 filtered off and washed with cold water. The filtrate is boiled in a 

 flask and the albumin precipitated. This is filtered off also and 

 the precipitate washed with cold water. The filtrates and wash 

 water are mixed and measured accurately. A portion of the 

 filtrate is placed in a buret, and this run into a boiling mixture of 

 20 c.c. Fehling's solution and 80 c.c. water. After the copper 

 has been completely precipitated the number of cubic centimeters 

 used is read. Twenty c.c. Fehling's solution correspond to 0.135 

 gram milk-sugar. 



The milk-sugar solution prepared for the O'Sullivan and 

 Defren method, or the solution from the casein and albumin de- 

 termination given on p. 184 can be used for titration. To facili- 



