14 



The Sachsse method, based on the hydrolysis of the starch with 

 dilute acid, fails because the presence of pentosans falsifies the 

 results by giving rise to reducing sugars (pentoses) which count as 

 dextrose, and also because actual destruction of dextrose occurs 

 during the prolonged heating with dilute acid. 



O'Sullivan's method, which is sufficiently accurate when pure 

 starch is employed, gives low results in the case of plant material, 

 owing to a loss of dextrin during purification of the solution after 

 the conversion with diastase, this purification being always necessary 

 to remove tannins, proteins, etc., from the plant material. 



The method now proposed is based on the fact that taka-diastase 

 in a few hours at 38° converts starch quantitatively into a mixture 

 of two sugars only, maltose and dextrose ; no loss of these sugars is 

 to be feared during the ordinary basic lead acetate process of puri- 

 fication. 



The details are as follows : — The plant material immediately 

 after picking is dropped into a large volume of 95 per cent, alcohol 

 containing 1 per cent, by volume of 0*880 ammonia. This destroys 

 the plant enzymes and prevents subsequent changes in the carbo- 

 hydrates. The material is then extracted for 18 to 24 hours with 

 boiling alcohol in a special large form of Soxhlet extractor, so as to 

 remove completely the sugars and other soluble substances. It is 

 then freed from alcohol by pressure and the press-cake is broken up, 

 dried in a steam oven for 18 hours, rapidly ground in a small mill 

 and bottled for analysis. 



Ten grams (or a suitable proportion) is dried to constant weight 

 at 100-110° in vacuo over phosphorus pentoxide and the results of 

 the analysis returned on the vacuum-dried weight. To estimate 

 starch, the dry material (previously extracted with water, if necessary, 

 to remove gums, amylans, etc.) is gelatinised with 200 c.c. of water 

 in a beaker flask heated for 2 hour in a water bath at 100°, the 

 mixture is cooled to 38°, 0*1 gram of taka-diastase and 2 c.c. of 

 toluene added, and the mixture left 24 hours for conversion to take 

 place ; it is then heated in boiling water to destroy the diastase and 

 the clear solution filtered through a fluted filter paper into a 500 c.c. 

 measuring flask ; the leaf residue is thoroughly washed several times 

 by decantation until about 475 c.c. of solution is obtained. The 

 necessary quantity of basic lead acetate solution (generally 5 to 

 25 c.c.) is then added to precipitate the tannins, etc., avoiding 

 as far as possible any great excess of lead ; tests should be made 

 after each small addition so as to ascertain when precipitation 

 is complete. When this is the case, the volume is made up to 

 500 c.c. at 15° and filtered; 100 c.c. of the filtrate are placed in a 

 110 c.c. flask, the slight excess for lead precipitated by adding solid 

 sodium carbonate and the volume adjusted to 110 c.c. 50 c.c. of 

 the filtrate from the lead carbonate are used to measure the reducing 

 power and another portion polarised in a 400 mm. tube. From the 

 values so obtained the quantity of maltose and dextrose present can 

 be calculated and the percentage of starch obtained. The values 

 obtained by Brown, Morris, and Millar for the reducing power of 

 dextrose and maltose are used as a basis of calculation. 



Several examples are given of the application of this method to 

 plant material, and the necessity is emphasised of removing optically 

 active substances soluble in water, such as gums. Special care is 



