Vin] FOODS AND FEEDING STUFFS 85 



„ 0.5124 P-I ^ P-S . 



S = : R = in which 



0.839 ' 1.852 



P = direct reading normal solution; 

 I = invert reading normal solution; 

 S = per cent of sucrose; 

 R = per cent of anhydrous raffinose. 



The above formula assumes that the polarizations are made at exactly 20°C. 

 If the temperature (T) is other than 20°C., the following formula should be used: 



P (0.4724 + 0-002 T) - I 

 0.899 - 0.003 T 



P-S 



Having calculated S, then R = 



1.852 

 CHEMICAL METHODS. 



1 8 DETERMINATION OF SUCROSE FROM REDUCING SUGARS BEFORE AND AFTER 

 INVERSION.— TENTATIV E. 



Determine the reducing sugars (clarification having been effected with neutral 

 lead acetate, never with basic lead acetate), as directed under 25, and calculate to 

 invert sugar from 27. Invert the solution as directed under 14 or 16, exactly 

 neutralize the acid, and again determine the reducing sugars, but calculate them 

 to invert sugar from the same table as referred to above, using the invert sugar 

 column alone. Deduct the percentage of invert sugar obtained before inversion 

 from that obtained after inversion, and multiply the difference by 0.95, the result 

 being the per cent of sucrose. The solutions should be diluted in both determina- 

 tions so that not more than 245 mg. of invert sugar are present in the amount 

 taken for reduction. It is important that all lead be removed from the solution 

 with potassium oxalate before reduction. 



Reducing Sugars, 

 invert sugar. 



Approximate Volumetric Method for Rapid Work. — Tentative. 



19 REAGENT. 



Soxhlet's Modification of Fehling's Solution. — Prepare by mixing, immediately 

 before use. equal volumes of (a) and (b). 



(a) Copper sulphate solution. — Dissolve 34.639 grams of copper sulphate (CuSO^ 

 5H2O) in water, dilute to 500 cc. and filter through prepared asbestos. 



(b) Alkaline tartrate solution. — Dissolve 173 grams of Rochelle salts and 50 grams 

 of sodium hydroxid in water, dilute to 500 cc, allow to stand for 2 days and filter 

 through prepared asbestos. 



20 STAND.^RDIZATION OF COPPER SOLUTION. 



Since the factor of calculation varies with the minute details of manipulation, 

 every operator must determine a factor for himself, using a known solution of the 

 pure sugar that he desires to determine, and keeping the conditions the same as 

 those used for the detern^ination. 



