242 METHODS OF ANALYSIS. 



and digest for a similar period with soda solution, after which treat for a few hours 

 with hot alkaline copper tartrate solution of the strength employed in sugar determi- 

 nations. Then wash the asbestos free from alkali, finally digest with nitric acid for 

 several hours, and after washing free from acid shake with water for use. In preparing 

 the gooch crucible load it with a film of asbestos one-fourth inch thick, wash this 

 thoroughly with water to remove fine particles of asbestos; finally wash with alcohol 

 and ether, dry for thirty minutes at 100 C. , cool in a desiccator and weigh. It is best to 

 dissolve the cuprous oxid with nitric acid each time after weighing and use the same 

 felts over and over again, as they improve with use. 



(2) DETERMINATION. 



Transfer 25 cc each of the copper and alkaline tartrate solutions to a 400 cc Jena 

 or Non-sol beaker and add 50 cc of reducing sugar solution, or, if a smaller volume of 

 sugar solution be used, add water to make the final volume 100 cc. Heat the beaker 

 upon an asbestos gauze over a Bunsen burner, so regulate the flame that boiling begins 

 in four minutes, and continue the boiling for exactly two minutes. Keep the beaker 

 covered with a watch-glass throughout the entire time of heating. Without diluting, 

 filter the cuprous oxid at once on an asbestos felt in a porcelain gooch crucible, using 

 suction. Wash the cuprous oxid thoroughly with water at a temperature of about 

 60 C., then with 10 cc of alcohol and finally with 10 cc of ether. Dry for thirty min- 

 utes in a water oven at 100 C., cool in a desiccator and weigh as cuprous oxid. 



N. B. The number of milligrams of copper reduced by a given amount of reducing 

 sugar differs when sucrose is present and when it is absent. In the tables following 

 the absence of sucrose is assumed except in the two columns under invert sugar, where 

 one for mixtures of invert sugar and sucrose (0.4 gram of total sugar in 50 cc of solution) 

 and one for invert sugar and sucrose when the 50 cc of solution contains 2 grams of 

 total sugar are given, in addition to the column for invert sugar alone. 



