98 METHODS OF ANALYSIS [Chap. 



electrolysis. Wash thoroughly with water, then break the current, wash with alco- 

 hol and ether successively, dry at about 50°C., and weigh. If preferred, the elec- 

 trolysis can be conducted in a beaker, the copper being deposited upon a weighed 

 platinum electrode. 



32 V. Electrolytic Deposition from Sulphuric and Nitric Acid S dulion. — Tenfative. 



Filter and wash as directed under 31 . Transfer the asbestos film from the cru- 

 cible to the beaker by means of a glass rod and rinse the crucible with about 30 cc. 

 of a boiling mixture of dilute sulphuric and nitric acids, containing 65 cc. of sul- 

 phuric acid (sp. gr. 1.84) and 50 cc. of nitric acid (sp. gr. 1.42) per liter. Heat and 

 agitate until solution is complete; filter and electrolyze as under 31 . 



33 VI. Electrolytic Deposition from Nitric Acid Sdution. — Tentative. 



Filter and wash as directed under 31 . Transfer the asbestos film and adhering 

 oxid to the beaker. Dissolve the oxid still remaining in the crucible by means. of 

 2 cc. of nitric acid (sp. gr. 1.42), adding it with a pipette and receiving the solution 

 in the beaker containing the asbestos film. Rinse the crucible with a jet of water, 

 allowing the rinsings to flow into the beaker. Heat the contents of the beaker until 

 the copper is all in solution, filter, dilute the filtrate to a volume of 100 cc. or more, 

 and electrolyze. When a nitrate solution is electrolyzed, the first washing of the 

 deposit should be made with water acidulated with sulphuric acid, in order to remove 

 all the nitric acid before the current is interrupted. 



34 VII. Reduction in Hydrogen. — Tentative. 



Deposit an asbestos film on a perforated platinum disc or cone contained in a 

 hard glass filtering tube, wash free from loose fibers, dry and weigh. Through this 

 tube, previously moistened, filter the cuprous oxid immediately, using suction. 

 Transfer the cuprous oxid to the tube through a removable funnel, and wash thor- 

 oughly with hot water, alcohol and ether successively. After drying, connect the 

 tube with a supply of dry hydrogen, heat gently until the cuprous oxid is com- 

 pletely reduced to metallic copper, cool in the current of hydrogen, and weigh. 

 If preferred, a Gooch crucible may be used for the filtration. 



Herzfeld Gravimetric Method. — Tentative. 



Method I. 



(For materials containing 1.5% or less of invert sugar and 98.5% or more of sucrose.) 



35 REAGENTS. 



The reagents and solutions used are described under 24. 



36 DETERMINATION. 



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 impurities by 

 neutral lead acetate, removing the excess of lead by means of sodium carbonate. 

 Place 50 cc. of the reagent and 50 cc. of the sugar solution in a 250 cc. beaker. Heat 

 this mixture at such a rate that approximately 4 minutes are required to bring it 

 to the boiling point, and boil for exactly 2 minutes. Add 100 cc. of cold, recently 

 boiled, water. Filter immediately through asbestos, and determine the copper 

 by one of the methods under 26, 29-34, respectively. Obtain the corresponding 

 oercentage of invert sugar from 37. 



