42 METHODS OF ANALYSIS. 



to sucrose. Multiply this by 0.95 to obtain the sucrose. The solution should 

 be diluted in both determinations so that not more than 245 nig of invert 

 sugar are present in the amount taken for the reduction, and should be properly 

 clarified with normal lead acetate and have the excess of lead removed before 

 the determinations. 



7. Reducing- Sugars. 



(See also Appendix, p. 241, for methods and tables of Munson and Walker.) 



(a) DETERMINATIONS REQUIRING THE USE OF SOXHLET'S MODIFICATION OF 

 FEHLING'S SOLUTION. 



(1) PREPARATION OF REAGENTS. PROVISIONAL. 



(a) Copper sulphate solution. Dissolve 34.639 grams of CuSO 4 . 5H 2 O in 

 water and dilute to 500 cc. 



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

 grams of sodium hydroxid in water and dilute to 500 cc. 



(c) Mixed solution. Mix equal volumes of solutions (a) and (&) immediately 

 before use. 



(2) VOLUMETRIC METHODS. 



(a) Approximate method for rapid work. Provisional. 

 (Applicable to invert sugar and dextrose.) 



Place 10 cc of the mixed copper reagent in a large test tube and add 10 cc of 

 distilled water. Heat to boiling, and gradually add small portions of the solu- 

 tion of the material to be tested until the copper has been completely precipi- 

 tated, boiling to complete the reaction after each addition. Two minutes' boil- 

 ing is required for complete precipitation when the full amount of sugar solu- 

 tion has been added in one portion. When the end reaction is nearly reached 

 and the amount of sugar solution to be added can no longer be judged by the 

 color of the solution, remove a small portion of the liquid and filter rapidly into 

 a small porcelain crucible or on a test plate ; acidify with dilute acetic acid, and 

 test for copper with a dilute solution of potassium ferrocyanid. The sugar 

 solution should be of such strength as will give a burette reading of 15 to 20 cc, 

 and the number of successive additions should be as small as possible. 



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 

 n pure sample of the sugar that he desires to determine, and keeping the condi- 

 tions the same as those used for the determinations. 



Standardize the solution for invert sugar in the following manner : 



Dissolve 4.75 grams of pure sucrose in 75 cc of water, add 5 cc of 38.8 per 

 cent hydrochloric acid, and invert as under the official method for sucrose. I>:I 

 41. Neutralize the acid exactly with sodium hydroxid and dilute to 1 liter. Ten 

 cubic centimeters of this solution contains 0.050 gram of invert sugar, which 

 should reduce 10 cc of the copper solution ; the copper solution should never be 

 taken as a standard, but should be check* "1 against the sugar. In case this 

 method is used for determining dextrose, pure dextrose must be used in stand- 

 ardizing the solution. 



(b)Soxhlet's method. Provisional. 



Make a preliminary titration to determine the approximate percentage of 

 reducing sugar in the material under examination. Prepare a solution which 

 contains approximately 1 per cent of reducing sugar. Place in a beaker 100 cc 



