iv PRESERVED MILK 213 



III. CONDENSED MILK. 



The best way to get a good average sample of condensed 

 milk is to pass a portion of the contents of a tin through a 

 sieve, and then, after stirring, the sample for analysis may be 

 drawn. Condensed milk is examined in exactly the same way 

 as ordinary milk, after weighing out the quantity required and 

 diluting it with water as advised in the directions for use. If 

 no directions are given the milk should be so diluted that the 

 specific gravity is slightly higher than that of ordinary milk, or 

 about T032. The percentage of fat is best determined by the 

 Rose-Gottlieb method (p. 52). The amount of sugar is found 

 by deducting the sum of the fat, protein, and salt from the dry 

 matter. If a quantitative determination of the amounts of 

 milk and cane sugar is wanted, the former is first made by 

 boiling with Fehling's solution after first precipitating the 

 protein substances (p. 85). Another portion is inverted with 

 hydrochloric acid, and the invert sugar determined by Fehling's 

 solution. The cane sugar can then be calculated from the 

 following formula: 



I = Invert sugar 

 M = Milk sugar. 



100 parts of invert sugar and 134 parts milk sugar give the 

 same quantity of Cu 2 0. 



In controlling the manufacture of condensed milk there are 

 several approximate methods which are used for determining 

 the amount of cane sugar. The two most important are : 



1. The total polarisation is first ascertained, and then the 

 amount of milk sugar is determined by multiplying the per- 

 centage of ash by 6 '5. The difference between the total sugar 

 and the milk sugar gives of course the cane sugar. 



2. The fat-free dry matter is first determined (a) from the 

 specific gravity and the percentage of fat, and then (b) from the 

 percentage of ash multiplied by 12. The quantity of cane 

 sugar is then obtained by subtracting b from a. 



A qualitative test for cane sugar in milk or in milk sugar is 



