170 THE ESTIMATION OF SUGARS. 



a red colour is produced on standing for 30 minutes, the presence 

 of cane sugar may be assumed. 



Detection and Estimation of Starch in Milk. Starch is occa- 

 sionally added to milk as an adulterant, and can be detected 

 by the blue colour given by iodine ; the iodine test is best applied 

 to the whey, as the proteins of milk interfere to some extent. 



Starch cannot be estimated with any great exactitude, as it 

 becomes partly converted into other bodies in milk, either by 

 means of an enzyme or by micro-organisms. 



To estimate it, the milk should be raised to boiling and cooled ; 

 the milk-sugar should be estimated by one of the gravimetric 

 methods given above, preferably by that of Wein. 20 c.c. of 

 milk should be diluted to about 95 c.c., 3 c.c. of 10 per cent, 

 acetic acid added, and the whole warmed to about 80 C., cooled 

 and made up to 100 c.c. 50 c.c. of the nitrate should be neutralised 

 carefully, and warmed to 65 C. (150 F.) ; 2 c.c. of a diastase 

 solution (containing the diastase from 2 grammes of malt) should 

 be added, and the solution kept at 65 C. for two hours. At the 

 expiration of that time it should be raised to boiling and evapor- 

 ated on the water-bath to less than 25 c.c. ; a little alumina 

 cream should be added, if the solution be not clear, and the total 

 made up to 25 c.c. This should be filtered and polarised. The 

 copper reduced by 10 c.c. of this solution should be estimated by 

 Wein's method. 



The results should be calculated as follows : Multiply the 

 polarisation by 2'5 ; the result will be the polarisation due to 

 milk-sugar, maltose, and dextrin ; calculate, from this and the 

 determination of milk-sugar, the polarisation due to maltose and 

 dextrin. 



Calculate the copper reduced from the 10 c.c. of diluted 

 filtrate = 4 c.c. of milk by the table on p. 162, and subtract from 

 this the milk-sugar present in this as calculated from the first 

 estimation ; the difference multiplied by 1*2 will represent 

 maltose. The polarisation due to maltose can be calculated, 

 using the value 137 for the [a] D , and the difference will be due 

 to dextrin. From this the percentage of dextrin can be calcu- 

 lated, using the value for [o] D of 200. 



The percentage of dextrin plus that of the maltose divided 

 by 1-056 will give that cf the starch. 



An approximate estimation may be made by subtracting from 

 the solids not fat the ash multiplied by 12. 



The estimation of starch is unsatisfactory, even if no other 

 foreign carbohydrate be present ; if other sugars have also been 

 added, it is nearly impossible to estimate them. 



