CH. VII.] MILK. 171 



Lactose. 



199. Boil a small portion of filtrate C with a little Fehling's 

 solution. A well-marked reduction is obtained, due to the presence 

 of a reducing sugar. 



200. A. Measure 2 cc. of filtrate C into a test-tube. Add 3 

 drops of glycerol ; add 10 drops of 20 per cent, copper sulphate by 

 means of a Dreyer's dropping pipette (fig. 5), and then 2 cc. of 20 

 per cent, sodium hydroxide. Boil the mixture and keep it boiling 

 for one minute. Allow the tube to stand. If the supernatant fluid 

 is blue, repeat the experiment with less copper. If the fluid is yellow, 

 repeat with more copper. The approximate amount of copper 

 that is reduced by the sugar in 2 cc. of the fluid is thus found. 



B. Measure 2 cc. of filtrate C into a test-tube and add 0-5 cc. 

 of pure concentrated hydrochloric acid. Boil gently over a small 

 flame for two minutes. Cool and add 14 drops of the copper 

 sulphate, and 3 drops of glycerol. Neutralise by means of 20 per 

 cent, sodium hydroxide, the neutral point being indicated by the 

 appearance of a grey precipitate. Now add a further 2 cc. of the 

 sodium hydroxide and boil for one minute. The whole of the copper 

 is usually reduced. The increase in the reducing power after boiling 

 with hydrochloric acid demonstrates that the sugar present in milk 

 is not glucose (see Ex. 103). 



201. To 5 cc. of Barfoed's solution add i cc. of filtrate C and 

 repeat Ex. 101. A reduction is not obtained. This experiment, in 

 conjunction with the previous one, indicates that the sugar present 

 is lactose or maltose. 



202. Concentrate about 25 cc. of filtrate C to about 10 cc. on 

 the water bath. Transfer this to a test-tube. Add i cc. of strong 

 acetic acid and proceed as in Ex. 109. Allow the yellow solution 

 that is obtained to cool slowly. A yellow precipitate of lactosazone 

 appears. Filter through a small paper, and suspend in about 4 cc. 

 of water. Boil. The precipitate dissolves. Allow to cool slowly 

 and examine the precipitate under the microscope. Lactosazone 

 usually crystallises in solid ovoid clumps with a projecting fringe of 

 fine needles. (" Hedge-hog " crystals.) 



