2 f 2 
Ingvar Jorgensen and Walter Stiles. 
taining 1% by volume of toluene which removes certain optically 
active leaf substances, among them dextrin if it is present. The 
residue, say 10 grams, containing the true starch, is then boiled with 
200 c.c. of water to gelatinise the starch. It is then left for 24 hours at 
38"C after addition of 0-1 gram of taka-diastase and 2 c.c. of toluene. 
After destroying the enzyme with 2 drops of concentrated sodium 
hydroxide and filtering, basic lead acetate is added (about 2-5 c.c.) 
and the volume made up to 500 c.c. The slight excess of lead is 
removed by the addition of the exact quantity of solid sodium 
carbonate necessary. After filtration the reducing power and optical 
rotation of the solution are determined. From these values the 
quantity of starch is calculated on the assumption that the only 
reducing and optically active substances present are glucose and 
maltose. In measuring the cupric-reducing power of all sugars 
examined the standard conditions laid down by Brown, Morris and 
Millar (1897) are employed, and their tables of the reducing power 
of maltose, glucose and fructose used. Similar tables for /-arabinose 
and /-xylose have been compiled by Daish (1914). 
3. Estimation of Dextrin (“ Soluble Starch ”). 
It was found by Davis and Sawyer (1916) that the leaf material 
from potato, after extraction with 80% alcohol contains large 
quantities of a substance readily soluble in water and having a high 
positive optical rotation. This and the reducing power were 
determined, and again after treatment with taka-diastase and basic 
lead acetate, and from the change in reducing power and rotation 
thus brought about, the dextrin was calculated. 
4. Estimation of Pentosans. 
These were estimated by Davis, Daish and Sawyer by distilling 
10 to F5 gram of the oven-dried leaf material with hydrochloric 
acid by the Krober-Tollens method and weighing the furfural 
produced as phloroglucide. 
5. Preparation of the Leaf Extract for Estimation of Sugars. 
Before estimating the sugars in the leaf extract containing 
them, the alcohol in the case of an alcoholic extract is replaced by 
water by evaporation of the alcohol and subsequent dilution with 
water. Davis, Daish and Sawyer evaporate the alcohol under 
reduced pressure (20-30 mm.) in a special distillation apparatus 
(Davis, 1913). By this means 3 litres of extract is reduced to 150 c.c. 
and diluted with water to 500 c.c., a little hot alcohol or toluene 
