HARRISON'S METHOD. 167 



R S = rotation due to sucrose. 

 R, = ,, before inversion. 



R v = after inversion corrected by multiplying by 2-2. 

 t = temperature in degrees Centigrade. 



The percentage of cane sugar is calculated from the rotation 

 deduced from this formula by the method given for milk-sugar, 

 bearing in mind that the [a] D of cane sugar is 66-5, not 52-5, 

 and that it does not require to be converted into anhydrous sugar. 



Harrison has shown that when cane sugar is inverted by 

 citric acid the polarimetric reading of the inverted cane sugar 

 is 42-03 + 0-5J for each 100 that the cane sugar polarised to 

 the right ; also that inversion of mixtures of milk and cane sugar 

 with citric acid fails to yield a clear solution. He proposes the 

 following method : About 75 grammes of condensed milk are 

 weighed out and diluted to 250 c.c. ; to 100 c.c. of this solution 

 3 c.c. of acid mercuric nitrate are added, the mixture shaken well 

 and filtered, and the filtrate is polarised in a 200 mm. tube. 

 50 c.c. or more of the filtrate are introduced into a clean dry 

 flask of about 100 c.c. capacity, and the whole weighed on a 

 balance turning to 0-02 gramme. The solution is then placed in 

 a briskly boiling water-bath, and kept there for seven minutes 

 exactly. The flask and its contents are then cooled, re weighed, 

 and the amount of water lost by evaporation replaced, and the 

 whole mixed thoroughly, filtered, and examined polarimetrically, 

 the temperature (I) at the time of polarisation being noted. 



The reading after inversion is subtracted from that before 



,,..,,, 142-66 -0-5? n .. 



inversion and divided by ^=- (t = degrees Centi- 

 grade), the result will be the reading due to cane sugar (C), and 

 this, subtracted from the reading before inversion, will be the 

 reading due to milk-sugar (M). 



From these readings the percentages of cane sugar and milk- 

 sugar are calculated as follows : 



Let W = number of grammes of condensed milk per 100 c.c., 

 F = percentage of fat, 

 P = percentage of proteins, 



then percentage of cane sugar is 



/W X Fx 1-08 + W x Px 0-84 "\ 



cx ^oo ~ j x i x ]oo, 



100 1-33 W 



and the percentage of anhydrous milk-sugar is 

 100 _ f W x F x 1-08 + W x P x 0-84 \ 



X 100 X FT06 X lV r 



