72 CHEMICAL EXAMINATION 



(6) A quantity of water in c.cms. equal to the fat X 1.11. 



(c) A quantity of water in c.cms. to reduce the scale readings 

 to percentages of milk sugar. 



(d) 3 c.cms. of acid mercuric nitrate. 



After thorough agitation, filter through dry papers and 

 polarise the filtrate. The percentage of milk sugar can be read 

 off directly in scale readings. 



The values of (c) are: 



(a) For polariscopes reading angular degrees. 



With 198.4 mm. tube 10.0 c.cms. 



With 200 mm. tube 10.85 c.cms. 



With 500 mm. tube 10.85 c.cms. (divide readings by 2.5). 



(6) For the Laurent sugar scale (100 = 21.67 angular degs.) 

 With 200 mm. tubes 2.33 c.cms. (divide readings by 5) 

 With 400 mm. tubes 2.33 c.cms. (divide readings by 10). 

 With 500 mm. tubes 2.33 c.cms. (divide readings by 12.5) 



(c) For the Ventzke scale (100 = 34.64 angular degrees). 

 With 200 mm. tube 6.65 c.cms. (divide readings by 3). 

 With 400 mm. tube 6.65 c.cms. (divide readings by 6). 

 With 500 mm. tube 6.65 c.cms. (divide readings by 7.5). 



Gravimetric Method. Dilute 25 c.cms. of milk with 400 

 c.cms. of water in a 500 c.cm. flask, add 10 c.cms. of No. 1, 

 Fehling solution and 4.4 c.cms. of N-NaOH solution; make 

 up to 500 c.cms., shake, and filter through a dry paper. The 

 filtrate should be acid and contain copper in solution. Place 

 25 c.cms. each of Fehling's solutions Nos. 1 and 2 in a beaker 

 and heat to the boiling point. When boiling briskly add 100 

 c.cms. of the milk serum and boil for six minutes. Filter imme- 

 diately through asbestos, supported by a platinum cone in a 

 hard glass filtering tube, with the aid of a suction pump, wash 

 thoroughly with boiling water and finally with alcohol followed 

 by ether. After drying, connect the tube with an apparatus 

 for supplying a continuous current of hydrogen and gently 

 heat until the cuprous oxide is completely reduced to the 



