2o6 Condensed Milk and Milk Powder 



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 degrees, and the corresponding number of 

 sucrose as 66.5 degrees. The lactose normal weight to read ioo- 

 degrees on the sugar scale for Laurent instruments is 20.496 grams, 

 and for Ventzke instruments, 32.975 grams. In case metric flasks, 

 are used the weights here mentioned must be reduced to 16.160 and 

 26.000 grams, respectively." 



Low's Volumetric Method, Modified 



PREPARATION OF REAGENTS 



"(a) Copper sulphate solution. — Dissolve 34.639 grams of 

 CuSO,, -5H 2 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. 



(cf) Standardization of the thiosulphate solution. — Prepare a 

 solution of sodium thiosulphate, dissolving 24.659 grams of pure 

 crystals to 1000 c.c. 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 hydroxid ; 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 c.c. of 80 per cent, acid) and boil for a minute. Cool to 

 room temperature and dilute to 1000 c.c. Titrate a known amount 

 (10 to 15 c.c.) of the copper solution, to which 10 c.c. of a 25 per 

 cent. Solution of pure potassium iodid has been added, with the 

 thiosulphate solution until the brown tinge has become weak, then 

 add sufficient starch liquor to produce a marked blue coloration. 

 Continue the titration cautiously until the color due to free iodin 

 has entirely vanished. The blue color changes toward the end to 

 a faint lilac. If at this point the thiosulphate be added drop by drop 

 and a little time be allowed for complete reaction after each addition, 



