FOODS AND FEEDING STUFFS. 41 



inversion. Free 50 cc of this filtrate from lead by treating with anhydrous 

 sodium carbonate, sodium sulphate or potassium oxalate, place in a 100 cc 

 flask, and add 25 cc of water. Then add, little by little, while rotating the 

 flask, 5 cc of hydrochloric acid, containing 38.8 per cent of the acid. Heat the 

 flask after mixing in a water bath which is at 70 C. The temperature of the 

 solution in the flask should reach 67 to 69 C. in two and one-half to three 

 minutes. Maintain a temperature of as nearly 69 C. as possible during seven 

 to seven and one-half minutes, making a total time of heating of ten minutes. 

 Remove the flask and cool the contents rapidly to 20 C. and dilute to 100 cc. 

 Polarize this solution in a tube provided with a lateral branch and a water 

 jacket, passing a current of water around the tube to maintain a temperature 

 of 20 C. 



The inversion may also be accomplished as follows : To 50 cc of the clarified 

 solution, freed from lead, add 5 cc of a 38.8 per cent solution of hydrochloric 

 acid and set aside during a period of twenty-four hours at a temperature not 

 below 20 C. ; or if the temperature be above 25 C. set aside for ten hours. 

 Make up to 100 cc at 20 C. and polarize at that temperature. This reading 

 must be multiplied by two, which gives the invert reading. In case it is neces- 

 sary to work at a temperature other than 20 C., which is allowable within 

 narrow limits, the volumes must be completed and both direct and invert 

 polarizations must be made at exactly the same temperature. The sucrose is 

 calculated by the following formula : 



q _100(P-I) 



T 



142.66 -~ 



S = per cent of sucrose. 

 P = direct reading. 

 I = invert reading. 

 T = temperature at which readings are made. 



(d) DETERMINATION OF SUCEOSE AND RAFFINOSE. OFFICIAL. 



(Of value chiefly in the analysis of beet sugars.) 



If the direct reading be more than 1 degree higher than the per cent of 

 sucrose as calculated by the formula given above, raffinose is probably present, 

 and sucrose and raffinose should be calculated by the following formula of 

 Creydt : 



P=the direct reading. 

 I=the invert reading. 

 S=the percentage of sucrose. 

 R=the percentage of anhydrous raffinose. 



0.5188 P I -p P S 

 0.8454 = ^85~ 



CHEMICAL METHODS. PROVISIONAL, 

 (a) DETERMINATION OF SUCROSE BY INVERSION AND REDUCTION. 



Determine the reducing sugars as Invert sugar in the sample and calculate 

 them by the proper table for invert sugar-sucrose mixtures (pages 43, 45), invert 

 the solution by one of the methods given under (c), exactly neutralize the acid, 

 determine the reducing sugars, and calculate them from the table for invert 

 sugar alone, page 45. Deduct the percentage of invert sugar obtained before 

 inversion from the amount obtained after inversion. This is the amount due 



