122 THE CARBOHYDRATES 



or other substances present which on hydrolysis would yield 

 reducing sugars. 



About 3 grams of the substance in as fine a state of divi- 

 sion as possible are covered with 50 c.c. of cold water and 

 shaken at frequent intervals ; after an hour the insoluble 

 portion is filtered off and washed with water until the total 

 filtrate measures 250 c.c. ; the addition of a little alumina shaken 

 up with water will frequently facilitate clear filtration. The 

 soluble carbohydrates contained in the filtrate may if de- 

 sired be determined both before and after inversion. 



The residue remaining on the filter paper is then transferred 

 to a flask with a 250 c.c. graduation mark and heated for two 

 and a half hours under a reflux condenser with 200 c.c. of water 

 and 20 c.c. of hydrochloric acid (sp. gr. I'I25). After cooling, 

 the solution is neutralized with caustic soda and made up to 

 250 c.c., whereupon it is filtered and the amount of glucose 

 contained in an aliquot portion of the filtrate is estimated by 

 Fehling's or Benedict's solution. The amount of glucose 

 found when multiplied by 0-9 gives the weight of starch. 



The following method for the estimation of starch in barley 

 is due to Horace T. Brown * : 



Five grams of the powdered or crushed grain are extracted 

 for three hours in a Soxhlet extractor with alcohol (sp. gr. 

 0-90); the residue is then .thoroughly boiled with 100 c.c. of 

 water, and, after cooling, to 57, 10 c.c. of active malt extract 

 are added and the mixture is set aside for one hour; it is 

 thereupon boiled and filtered into a flask with a 200 c.c. 

 graduation mark ; the residue is thoroughly washed with water, 

 and, after cooling, the filtrate and washings are made up to 

 200 c.c. The cupric reduction of 20 c.c. of the solution is 

 determined under the conditions laid down by Brown, Morris 

 and Millar, f the maltose being calculated according to Table 

 XI in that paper (loc. cit. y p. 100), after correction for the reduc- 

 tion due to the malt extract. The starch equivalent to this 

 maltose is then ascertained by assuming that 84*4 parts of 

 maltose correspond to 100 parts of starch. 



The malt extract is prepared by digesting 10 grams of 

 fresh finely-ground malt for two to three hours with 200 c.c. 

 of water and filtering. 



* Horace T. Brown : " Trans. Guiness Research Lab.," 1903, I, 89. 

 f Brown, Morris and Millar : " J. Chem. Soc., Lond.," 1897, 7* 94 



