64 SUBSTANCES SOLUBLE IN ALCOHOL. 



This method is not, however, always successful, and com- 

 pounds of the alkaloids differing considerably in solubility, etc., 

 must be looked for, applicable to the separation to be effected. 

 Quinine may be separated from quinidine by precipitation 

 with Rochelle salt, quinidine from cinchonine by iodide of 

 sodium, etc. Use may also be made of the difference in equi- 

 valent weights. (Compare the estimation of brucine in presence 

 of strychnine in 174.) See also 180 to 183. 



EXAMINATION FOR GLUCOSES SOLUBLE IN ALCOHOL. 



70. Detection and Estimation of Glucoses soluble in Alcohol. 

 Both glucoses and cane-sugars may be present in that part of 

 the alcoholic extract ( 48) which is soluble in water, but the 

 amount can be but small, since the material is macerated at the 

 ordinary temperature. It must, however, be taken into account, 

 in order to avoid error. If the alcoholic extract contain no tannin 

 or bitter substance, the aqueous solution may be tested for glucose 

 with Fehling's solution ( 83) without further treatment ; if found 

 it may be determined quantitatively. 



Sugar may also be qualitatively tested for by adding to the 

 liquid under examination first potash and then dilute solution of 

 sulphate of copper, as long as the cupric hydrate first formed is 

 redissolved. Excess should be avoided. The liquid may now be 

 divided into two portions, one of which may be warmed and 

 the other allowed to stand in the cold in order to ascertain whether 

 reduction takes place at the ordinary temperature, as well as on 

 heating. 



If the glucose is accompanied by such substances as tannin, 

 etc., the filtrate obtained after addition of acetate of lead in their 

 quantitative estimation ( 49, 52), or after precipitation of a 

 separate quantity with basic acetate, may be treated, together 

 with the washings, with a slight excess of sulphuric acid, filtered, 

 washed and made up to a known volume. The sugar may then 

 be estimated quantitatively with Fehling's solution. The result 

 must be added to the amount found in the aqueous extract ( 83). 

 Part of the solution may be boiled for half an hour with 1 to 2 

 per cent, of sulphuric or hydrochloric acid in a flask fitted with 

 an upright condenser. If more sugar be found after such treat- 

 ment, the difference is to be calculated as saccharose ( 85). 



