214 QUANTITATIVE ANALYSIS. 



flask is filled up to the mark with water. Let settle and take 

 out 200 cc. of the supernatant fluid (using a 100-cc. pipette) ; 

 instead of this we may also filter through a dry filter and 

 measure off 200 cc. of the filtrate. Place the measured fluid 

 in a 400-cc. flask, add 15 cc. of hydrochloric acid, and heat 

 two and one-half hours in an actively boiling water-bath, to 

 convert the dextrin into glucose; let cool, place in a 300-cc. 

 measuring-flask, nearly neutralize with caustic soda solu- 

 tion (if too much alkali has been added, make faintly acid 

 again with dilute hydrochloric acid), and make the sugar 

 determination best gravimetrically with 50 cc. or titrate 

 according to Fehling (the latter method is to be recommended 

 only with larger quantities of starch). Instead of this 

 method, that of L. Liebermann, which requires no autoclave, 

 may also be used. (See Analysis of Bread, page 229.) 



6. Determination of the Total Phosphorus. (a) By 

 fusing with the oxidizing mixture. About 1 to 1.3 g. of the 

 material (accurately weighed) is fused with 20 g. of the 

 oxidizing mixture. It is best to proceed as follows: About 

 two-thirds of the oxidizing mixture is placed in a smooth 

 mortar , a hole is made in the mixture with the pestle, the 

 material placed in this, ground, and the mixture transferred 

 to the platinum dish. The mortar is then rinsed out with 

 the rest of the oxidizing mixture in two portions and, if neces- 

 sary, wiped out with a feather or a brush. These portions 

 are placed at the side of the dish, and the heating is also 

 begun here and continued until all the organic substance is 

 burned. It is very advantageous, towards the end of the 

 operation, to hold the dish in the flame with the tongs. The 

 complete combustion is then more readily accomplished. 

 The fused mass is then dissolved in water, the solution intro- 

 duced, without loss, by means of a funnel, into a flask, nitric 

 acid cautiously added to strongly acid reaction (20 to 25 cc.) 

 and heated on the sand-bath, with a funnel set in the neck of 



