86 METHODS OF ANALYSIS [Chap. 



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 hydrochloric 

 acid (sp. gr. 1.20) and invert as directed under 14. Neutralize the acid with sodium 

 hydroxid solution and dilute to 1 liter. Ten cc. of this solution contain 0.050 gram of 

 invert sugar, which should reduce 10 cc. of the reagent. The strength of the copper 

 solution should never be taken as a constant, but should be checked against the 

 sugar. 



21 



DETERMINATION. 



Place 10 CC. of the reagent in a large test tube and add 10 cc. of water. Heat to 

 boiling, and add gradually small portions of the solution of the material to be tested 

 until the copper has been completely reduced, boiling after each addition to com- 

 plete the reaction. Two minutes' boiling is required for complete reduction when 

 the full amount of sugar solution has been added in one portion. When the end 

 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 dilute potassium ferrocyanid solution. The sugar 

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

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



Soxhlet Volumetric Method. — Tentative. 



22 REAGENT. 



The reagent used is described under 19. 



23 DETERMINATION. 



Make a preliminary titration to determine the approximate percentage of reduc- 

 ing sugar in the material under examination. Prepare a solution which contains 

 approximately 1% of reducing sugar. Place in a beaker 100 cc. of the reagent and 

 approximately the amount of the sugar solution for its complete reduction. Boil 

 for 2 minutes. Filter through a folded filter and test a portion of the filtrate for 

 copper by use of dilute acetic acid and dilute potassium ferrocyanid solution. Re- 

 peat, varying the volume of sugar solution, until 2 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 2 readings is taken as the volume 

 of the solution required for the complete precipitation of 100 cc. of the reagent. 



Under these conditions 100 cc. of the reagent require 0.494 gram of invert sugar 

 for complete reduction. Calculate the percentage by the following formula: 



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



100 cc. of the reagent; 



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



100 X 0.494 \ t ■ ^ 



— — = per cent of mvert sugar. 



VW 



GRAVIMETRIC METHODS 



Munson and Walker General Methods — Tentative. 



24 REAGENTS. 



(a) Asbestos. — Digest the asbestos, which should be the amphibole variety, with 

 dilute hydrochloric acid (1 to 3) for 2-3 days. Wash free from acid, digest for a 



