THE DETERMINATION OF REDUCING SUGARS 533 



to tables based on the examination of known quantities of reducing sugars. 

 That due to Munson and Walker is given in the Appendix. 



(b) To a fixed quantity of cupric salt is gradually added the solution 

 containing the unknown quantity of reducing sugar. The addition is 

 continued until all the cupric salt is reduced. Of routines following the first 

 method there are many. Those most in use have been arranged by Brown, 

 Morris and Millar 6 , by Allihn 7 , by Defren 8 and by Munson and Walker 9 , 

 whose method is selected for description. 



Munson and Walker's Method. Two solutions are required : 



! 34*639 grams CuSO 4 5 H 2 O in 500 c.c. 



2. 173 grams potassium sodium tartrate and 51-6 grams sodium hydrate 

 in 500 c.c. 



The quantity of sodium hydrate present should be controlled by analysis. 



Place 25 c.c. each of the above solutions in a 400 c.c. Jena or non-sol 

 beaker, followed by 50 c.c. of the reducing sugar solution. Heat upon 



FIG. 343 



asbestos gauze so that boiling begins in four minutes and continue ebullition 

 for two minutes. Filter at once and determine the copper in the pre- 

 cipitate by one or other of the methods given below : 



The Filtration. The filtration of the precipitated cuprous oxide may be 

 made through asbestos, contained in a glass tube or Gooch porcelain crucible ; 

 through an "alundum" crucible; or again through spongy platinum. With 

 these apparatus the filtration is effected under reduced pressure. Paper 

 may be used in the absence of other appliances, but an error is introduced 

 due to the absorption of copper sulphate by the paper. 



The asbestos used for filtration should be the long fibre variety. It 

 should be prepared for use by digesting with 33 per cent, hydrochloric acid 

 for 48 hours, followed by digestion for an equal period with 10 per cent, 

 caustic soda. After washing free from alkali it is preserved suspended in 

 water. 



The Soxhlet tube, Fig. 343, consists of a glass tube, about six inches 

 long in all ; the upper portion is about three inches long and half an inch 

 in diameter, and terminates in a concave bottom, to which is attached a 

 short capillary of about I /32 in. bore ; the lower half is about three inches 

 long and in diameter tapers from i /2 to 3 /i6 in. It is prepared for use 

 thus : A plug of glass wool is placed on the concave bottom of the tube 



