106 THE CARBOHYDRATES 



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., 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. 



DEXTRINS. 



The term dextrin is applied to substances which are poly- 

 meric with starch and are formed from it by the action of heat 

 alone or of diastase or mineral acids. In the plant dextrins 

 may occur as transitory substances whenever starch is being 

 acted upon by diastase ; further, certain dextrins may occur in 

 a more permanent form. Thus the sap of the epidermal cells 

 of Arum italicum turn reddish-violet on the application of 

 iodine. The aqueous extract of such cells gives on evapora- 

 tion a transparent sticky substance. This also gives with 

 iodine a violet coloration ; after boiling, the colour reaction 



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

 f Brown, Morris and Millar : " J. Chem. Soc., Lond.," 1897, 7 1 * 94- 



