CHAPTER X. 



THE ESTIMATION OF SUGARS. 



Estimation of Milk-Sugar. Milk-sugar is generally estimated 

 indirectly, as it is not possible to isolate it quantitatively from 

 milk in a state of purity. The following method may, however, 

 be used to obtain an approximate determination of the milk- 

 sugar : 



By Alchohol. To 10 c.c. of milk add 20 c.c. of 90 per cent, 

 alcohol, mix well and filter ; of the filtrate take 10 or 15 c.c., 

 evaporate to dryness on a water-bath and dry at 100 C. (212 F.) 

 till the weight is constant. Ignite the residue and weigh the 

 ash. The weight of the residue less the weight of the ash will 

 give the weight of the milk-sugar. The volume of the aqueous 

 portion must be calculated ; on mixing alcohol and water a 

 contraction takes place ; this with the quantities given is 0-4 c.c ; 

 the volume occupied by the protein is on the average 0-25 c.c. ; 

 the volume of the fat is obtained by multiplying the percentage 

 by weight by 0-111. 



The percentage of milk-sugar is obtained by the following 

 formula : 



, ^ 80 -(0-65 + 0-111 F) x(B _ A)xl0x .l >t 



where 



x = number of c.c. taken for estimation of residue. 

 D = specific gravity of milk. 

 F = percentage of fat in milk. 

 R = weight of residue. 

 A = ash. 

 M = percentage of milk-sugar. 



This method has a tendency to yield results about 0-2 to 0-3 per 

 cent, too high. 



By the Polariscope (Fig. 22). The quickest method of 

 milk-sugar estimation is by the polariscope ; before the milk 

 can be polarised it is necessary to remove completely the fat 

 and proteins which interfere either by making the solution too 

 opaque for reading or by polarising to the left. 



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