Vni] FOODS AND FEEDING STUFFS 83 



DETERMINATION OF SUCROSE IN THE ABSENCE OF RAFFINOSE. 



(In the presence of much levulose, as in honeys and fruits products, the optical 

 method for sucrose gives too high a result.) 



14 By Polarization Before and After Inversion with Hydrochloric Acid. — Official. 



Dissolve the normal weight (26 grams) of the substance in water, add basic lead 

 acetate carefully, avoiding any excess, then 1-2 cc. of alumina cream, shake, and 

 dilute to 100 metric cc, filter, rejecting the first 20 cc. of the filtrate, cover the 

 filter with a watch glass and, when sufficient filtrate is collected, polarize in a 200 

 mm. tube. The reading so obtained is the direct reading (P of formula given be- 

 low) or polarization before inversion. For the invert reading, remove the lead from 

 the solution either (1) by adding anhydrous potassium oxalate, a little at a time, 

 to the remaining solution, avoiding an excess and removing the precipitated lead 

 by filtration; or, (2) by adding anhydrous sodium carbonate under the same con- 

 ditions. Introduce 50 cc. of the lead-free filtrate into a 100 cc. flask (if sodium 

 carbonate was used for removing the lead, neutralize carefully the excess of sodium 

 carbonate with a few drops of dilute hydrochloric acid) and add 25 cc. of water. 

 Then add, little by little, while rotating the flask, 5 cc. of hydrochloric acid, (sp.gr. 

 1.20). Heat the flask after mixing, in a water bath kept at 70°C. The temperature 

 of the solution in the flask should reach 67°-69°C. in 2|-3 minutes. Maintain a 

 temperature of as nearly 69°C. as possible for 7-7J minutes, making the total time 

 of heating 10 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, maintaining a temperature of 20°C. This reading must be 

 multiplied by 2 to obtain the invert reading. If it is necessary to work at a tem- 

 perature 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 inversion may also be accomplished as follows: (1) To 50 cc. of the clarified 

 solution, freed from lead, add 5 cc. of hydrochloric acid (sp. gr. 1.20) and set aside 

 for 24 hours at a temperature not below 20°C.; or ,(2) If the temperature be above 

 25°C. set aside for 10 hours. Make up to 100 cc. at 20°C. and polarize as directed 

 above. 



Calculate sucrose by one of the following formulas: 



For substances in which the invert solution contains more than 12 grams of invert 

 sugar per 100 cc. — The following formula is to be used when substances like raw 

 sugars are polarized: 



^ 100 (P - I) . , . , 



S = in which 



T 

 142.66 - - 



S = per cent of sucrose; 



P = direct reading normal solution ; 



I = invert reading normal solution; 



T = temperature at which readings are made. 

 For substances in lohich the concentration of the invert solution is less than 12 grams 

 ■per 100 cc. — The following formula, which takes into account the concentration of the 

 sugar in solution, should be used in all other cases. 



