DAIRY PRODUCTS. 



119 



]>< !< / nihntlioii <>f roliunc of mill: sample. 



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

 102.4 cc for a Laurent or 102.6 cc for a Ventzke polariscope (Mohr cc). Add 



c < of mercuric nitrate solution or 30 cc of mercuric iodid solution (an excess 

 :ose reagents does no harm), fill to the mark, agitate, filter through a dry 

 filter, and polarize. It is not necessary to heat before polarizing. In case a 

 200 mm tube is used, divide- the polariscope reading by 3 when the sucrose 

 normal weight for the instrument is 16.19 grams, or by 2 when the normal 

 weight for the instrument is 26.048. When a 400 mm tube is used, these 

 divisors become 6 and 4, respectively. For the calculation of the above table 

 the specific rotary power of lactose is taken as 52.53, and the corresponding 

 number for sucrose as 66.5. The lactose normal weight to read 100 on the 

 sugar scale for Laurent instruments is 20.496 grams, and for Ventzke instru- 

 s. o^.nin jirams. In case metric flasks are used the weights here mentioned 

 mr.st be reduced to 16,160 and 26.000 grams, respectively. 



(b) GRAVIMETRIC METHOD. OFFICIAL. 



(1) PREPARATION OF THE MILK SOLUTION. 



Dilute 25 cc of the milk with 400 cc of water and add 10 cc of a solution of 

 copper sulphate of the strength given for Soxhlet's modification of Fehling's 

 solution, page 42, " VI. General Methods ; " add about 7.5 cc of a solution of 

 potassium hydroxid of such strength that one volume of it is just sufficient to 

 completely precipitate the copper as hydroxid from one volume of the solution 

 of copper sulphate. Instead of a solution of potassium hydroxid of this strength 



j&S cc of a half-normal solution of sodium hydroxid may be used. After the 

 addition of the alkali solution the mixture must still have an acid reaction and 



I contain copper in solution. Fill the flask to the 500 cc mark, mix, and filter 



I through a dry filter. 



(2) DETERMINATION. 



Proceed as directed under "VI. General Methods" 



! s 



6. Fat. 

 (a) BABCOCK ASBESTOS METHOD. OFFICIAL. 



Extract the residue from the determination of water by the Babcock asbestos 

 ! method with anhydrous ether until all the fat is removed, evaporate the ether, 

 jdry the fat at the temperature of boiling water, and weigh. The fat may also 

 jbe determined by difference, drying the extracted cylinders at the temperature 

 of boiling water. 



