QUALITATIVE AND QUANTITATIVE ANALYSIS 75 



Place 5 cubic centimeters of the micro reagent in a 50-cubic 

 centimeter Pyrex test tube and to this add from 1 to 5 cubic 

 centimeters, depending upon the quantity of sugar present, of 

 the clarified sample. If less than 5 cubic centimeters of sample is 

 taken, add sufficient water to make the total volume 10 cubic 

 centimeters. At the same time make up a blank with 5 cubic 

 centimeters of water and 5 cubic centimeters of reagent. Stopper 

 the test tubes with loose-fitting corks, to prevent oxidation from 

 the air, and heat for 15 minutes in a boiling water bath. Cool 

 in running water, add 5 cubic centimeters of IN H2SO4, shake 

 well, let stand 1 minute and titrate with O.OOSiV thiosulphate 

 and starch paste as an indicator. Add the starch solution when 

 the solution has turned a light straw color which indicates that 

 only a trace of iodine remains. Continue the titration with 

 thiosulphate until the blue color of the starch iodine compound 

 completely disappears. The end point is very sharp — within 

 1 to 2 drops of thiosulphate. 



Calculation may be made directly from the micro-sugar table. 

 The titration of the sample in cubic centimeters of O.OOSA^ 

 thiosulphate is subtracted from the titration of the blank, 

 the difference found in the table and read in milligrams of 

 glucose. The glucose per cubic centimeter of sample is then 

 calculated from the glucose found in the aliquot taken. 



When 1 cubic centimeter of culture is taken for the direct deter- 

 mination, this method will accommodate samples containing up to 

 0.20 per cent glucose. If the sugar percentage is greater, the 

 sample must be diluted. For a sugar concentration of about 0.50 

 per cent, a convenient dilution would be 10 cubic centimeters made 

 up to 50 cubic centimeters and a 1 cubic centimeter aUquot 

 taken. 



6. Lignins. — ^Lignins are prepared and determined by treating 

 natural or decomposed organic tnaterials with 42 per cent hy- 

 drochloric acid,^ 72 per cent sulphuric acid or a mixture of 

 hydrochloric and sulphuric acids; the acids decompose all the 

 celluloses, pentosans and proteins, leaving the lignins unattacked. 

 Four 2-gram portions of organic material, such as straw, ground 

 wood shavings, etc., are treated with ether to remove the fats 



1 WiLLSTATTER, R., and L. Zeichmeister, Ber. deut. Chem. GeselL, 46: 

 2401, 1913. ScHWALLEE, H., Papi&rfabr., 23: 174-177, 1925. 



