256 METHODS OF ANALYSTS. 



continue the boiling and stirring for thirty minutes. Replace the water lost by evapo- 

 ration and immerse the beaker in a water bath kept at 55 to 60 C. When the liquid 

 has cooled to the temperature of the bath, add 20 cc of a freshly prepared extract of 

 malt a and digest the mixture for two hours with occasional stirring. Boil a second 

 time for thirty minutes, dilute, cool, and digest as before with another 20 cc portion of 

 malt extract. Heat again to boiling, cool, and transfer to a 250-cc flask. Add 3 cc of 

 alumina cream, make up to the mark, and filter through a dry paper. & Conduct the 

 hydrolysis of 200 cc of the filtrate and determine the reducing power of the resultant 

 solution as directed under "Crude Starch" in the preceding section (10), except that 

 the treatment with basic lead acetate solution and its removal with sulphuric acid are 

 omitted. Introduce a correction for dextrose, due to the added malt extract, as deter- 

 mined by accompanying blank analyses. 



12. Fat. 



Desiccate 2 grams of the material for two or three days or until the moisture is prac- 

 tically removed. Extract with anhydrous ether in a Tollens, Johnson, or Wiley fat 

 extractor until no more fat is removed. Grind and repeat the extraction. Allow the 

 ether to evaporate and dry the residue at 100 C. until the weight is constant. 



13. Sucrose and Lactose (Dubois's Method). c 



Extract the fat from 13 grams of the sample by shaking and centrifuging twice with 

 100 cc of gasoline, separating the solvent by decantation. To the residue add 100 cc 

 of water and shake for ten minutes. Add 5 cc of basic lead acetate solution (p. 40), 

 filter, and remove the excess of lead. Allow 25 cc of this solution to stand over night 

 to destroy birotation, and polarize. Multiply readings by 2. Invert 50 cc of the 

 above filtrate as described on page 40 (c), nearly neutralizing the acid after cooling 

 with sodium hydroxid solution, and make up to 100 cc. Bring to temperature at 

 which direct readings were made and polarize, and also polarize at 86 in a water 

 jacketed tube; multiply all invert readings by 4. 



Calculate the approximate weight of sucrose and lactose present in the 13 grains 

 by the following formulae: 



Grams of sucrose = - ><13 

 142.66- 



Grams of lactose ^A^X l.nxl.05Xl3 = 19^2c 



a=direct readings, normal weight. 

 b=invert readings, normal weight. 

 c=invert readings, normal weight at 86 C. 



From the total amount of sugar found by the above, obtain the value of x from the 

 table below and calculate sugars as follows: 



1 ' X =per cent of sucrose. (1.473c)x=per cent of lactose. 

 142.60 - , 



2 grams of sugar in sample, x=101.2 



4 grams of sugar in sample, x=102.5 



6 grams of sugar in sample, x=103.6 



8 grams of sugar in sample, x=104.8 

 10 grams of sugar in sample, x= 106.05 

 15 grams of sugar in sample, x=109.40 

 20 grams of sugar in sample, x=112.40 



o Prepared as directed under "VI. General Methods," 8 (b), (1), page 53. 



b The residue on the paper at this point should show no signs of starch when examined microscopically. 



ej. Amer. Chem. Soc., 1907, 29: 556. 



