FOODS AND FEEDING STUFFS. 



43 



of the mixed copper reagent and approximately the amount of the sugar solu- 

 tion for its complete reduction. Boil for two minutes. Filter through a folded 

 filter and test a portion of the filtrate for copper by use of acetic acid and potas- 

 sium ferrocyanid. Repeat the test, varying the volume of sugar solution, until 

 two successive amounts are found which differ by 0.1 cc, one giving complete 

 reduction and the other leaving a small amount of copper in solution. The mean 

 of these two readings is taken as the volume of the solution required for the 

 complete precipitation of 100 cc of the copper reagent. 



Under these conditions 100 cc of the mixed copper reagent require 0.475 

 gram of anhydrous dextrose or 0.494 gram of invert sugar for complete reduc- 

 tion. Calculate the percentage by the following formula : 



V=the volume of the sugar solution required for the complete reduction 



of 100 cc of the copper reagent. 

 W=the weight of the sample in 1 cc of the sugar solution. 



Then 



100X0.475 



or 



vw 



100X0.494 



=per cent of dextrose, 



=per cent of invert sugar. 



(3) GRAVIMETRIC METHODS. 



(a) Invert sugar. Provisional. 



(a) Determination in materials containing 1 per cent or less of invert sugar 

 and 99 per cent or more of sucrose : 



Prepare the solution of the material to be examined so as to contain 20 grams 

 in 100 cc, free from suspended impurities by filtration and from soluble impuri- 

 ties by normal lead acetate, removing the excess of lead by means of sodium car- 

 bonate. Place 50 cc of the mixed copper reagent and 50 cc of the sugar solution 

 in a beaker of 250 cc capacity. Heat this mixture at such a rate that 

 approximately four minutes are required to bring it to the boiling point, and 

 boil for exactly two minutes. Add 100 cc of cold, recently boiled, distilled 

 water. Filter immediately through asbestos and determine the copper by 

 one of the methods given under (c), page 51. 



Obtain the corresponding percentage of invert sugar by the use of the fol- 

 lowing table : 



Hertzf eld's table for the determination of invert sugar in materials containing 1 per cent or 

 less of invert sugar and 99 per cent or more of sucrose. 



87404 Bull. 10700 5 



