348 CHemicar, ‘Tests AND ANALYSIS 
Volume of Milk Corresponding to a Lactose Double Normal 
Weight. 
Volume of Milk | Veee ae Milk 
stents = . for a Lactose . ee eae | for a Lactose 
Specific Gravity Double Normal Specific Gravity | Double Normal 
of Milk Weight Ventzke ot Milk | Weight Ventzke 
Scale Scale 
Cec. Ce? 
1.024 64.25 1.031 63.80 
1.025 64.20 1.032 63:70 
1.026 64.15 1.033 63.70 
1.027 64.05 1.034 63.65 
1.028 64.00 
1.029 63.95 1.035 63.55 
1030 | 63.90 1.036 63.50 
Low's Volumetric Method Modified. 
Preparation of Reagents. 
“(a) Copper sulphate solution.—Dissolve 34.039 grams of 
CuSO, .5H,O in water and dilute to 500 c.c. 
(b) Alkaline tartrate solution—Dissolve 173 grams of Ro- 
chelle salts and 50 grams of sodium hydroxid in water and dilute 
to 500 c.c. 
(c) Mixed solution.—Mix equal volumes of solutions (a) and 
(b) immediately before use. 
(d) Standardization of the thiosulphate solution.—l’repare a 
solution of sodium thiosulphate, dissolving 24.059 grams of pure 
crystals to 1,000 cc. Weigh 6.36 grams copper foil. Dissolve by 
warming in minimum amount of nitric acid and water required. 
Boil to expel the red fumes, add 160 c.c. strong bromine water and 
boil until the bromine is thoroughly expelled. Remove from the 
heat and add a slight excess of strong ammonium hydronid; 223 c.c. 
is about the right amount. Again boil until the excess of ammonia 
is expelled, as shown by a change of color of the liquid, and partial 
precipitation. Now add a slight excess of strong acetic acid (100 
to 130 cc. of 80 per cent acid) and boil for a minute. Cool to 
room temperature and dilute to 1,000 c.c. Titrate a known amount 
(10 to 15 cc.) of the copper solution, to which 10 c.c. of a 25 per 
cent solution of pure potassium iodid has been added, with the 
