16 



Take 50 cc of the clarified solution freed from lead, add 25 cc of water, and add, 

 little by little, while rotating the flask, 5 cc of hydrochloric acid containing 38.8 per 

 cent of the acid; and heat the contents of the flask, after mixing, on a water bath 

 heated to 70 C. The temperature of the solution in the flask should reach 67 to 

 70 in two and one-half to three minutes. Maintain a temperature of as nearly 69 

 as possible during seven to seven and one-half minutes, making a total time of heat- 

 ing of ten minutes. Remove the flask and cool the contents rapidly to 20 C. , and 

 dilute the solution 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. Multiply the invert reading, made at 20 C., by 2. 



Or- 



Take 50 cc of the clarified solution freed from lead, add 5 cc of hydrochloric acid 

 containing 38.8 per cent of acid, 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. 



13. DETERMINATION OF SUCROSE. 



(a) BY POLARIZATION. 



Calculate sucrose from the direct and the invert polariscopic readings according to 

 the following formula: 



When the polarizations are made at 20 C. : 



142.662- 



P=the direct reading. 

 J=the invert reading. 

 /S'=the percentage of sucrose. 



Should the temperature (t) vary from 20, which is permissible within narrow 

 limits, in the absence of raffinose use the following formula: 



^_100 (P-J) 

 142.66-^ 



On page 78, section 13, b, line 8, change "1 per cent" to "0.50 per 

 cent." 



(b) BY REDUCTION. 



Where only a small amount of cane sugar is present it is best determined by calcu- 

 lation from the increase in reducing sugars after inversion. For this purpose treat 5 

 grams of jelly, sirup, or other fruit product dissolved in a sufficient amount of water, or 

 25 grams of juice or fresh fruit, with lead subacetate in excess, make up to 100 cc and 

 filter. Remove the excess of lead with sodium sulphate and invert 50 cc in a 100 cc flask 

 with 5 cc of hydrochloric acid. After inversion neutralize the add with sodium liydroxid 

 and increase the volume to 100 cc. Dilute so that the solution does not contain more 

 than 0.50 per cent of reducing sugar. The clarified products obtained for polarization 

 under "13" before and after inversion may also be used after suitable dilution for the 

 determination of the reducing power. The per cent increase in reducing sugar after 

 inversion multiplied by 0.95 equals per cent of cane sugar. 



On page 78, section 14, lines 8 and 9, for the words "Use Allihn's 

 method for the determination (p. 49)," substitute "Use the official 

 method for the determination of invert sugar as given in Bui. 46, p. 

 33 (c) (1) (a) and (b)." 



