ESTnLA.TION OF CAXE SUGAR. 103 



for 10 minutes with, citric acid, and recommend that the time of 



heating should be continued for 40 minutes. 



By Invertase. — The best method of estimating cane sugar 



depends on the hydrolysis of cane sugar by invertase, the enzyme 



of yeast. This is carried out as follows : — Estimate the rotation 



due to milk and cane sugar by polarisation of the solution 



obtained by precipitation with mercxuic nitrate (100 c.c. of milk 



should be taken). 25 c.c. of the solution are placed in a flask, 



a drop or two of phenolphthalein added, and dilute caustic 



soda solution run in till neutral. This solution is filtered into 



a 50 c.c. flask, and the precipitate washed with water till the 



filtrate and washings measure about 45 c.c. 0*05 gramme of 



invertase, or 1 gramme of yeast, is added, together with a drop 



of acetic acid and a few drops of toluene, and the whole made 



up to 50 c.c. The flask is corked and allowed to remain at about 



55° (131° F.) for five hours. A little alumina cream is added 



and the whole made up to 55 c.c, filtered, and polarised ; the 



temperature at which the solution is polarised should be noted. 



55 

 The reading should be multiplied by ^^^ = 22 ; tin- readinfj; due 



to cane .su^'ar is found by the formula 

 „ 100 (R, - R„) 



1*8 = r 



wi-m - 2" 



E.^ = rotation duo to suci-osc. 



■R = ,, before inversion. 



I; _ ,, after inversion corrected by multiplying 1>\' '1"1. 

 I = teni|ii'raturi' in degree.^ 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 [aji, of cane sugar is 66'5' instead of 

 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 o:! + O'bt for each 100" that the cane sugar polarised to 

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

 with titric 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 well shaken 

 and filtered, and the filtrate is polarised in a 20U mm. tube. 

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

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

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



