136 THE CARBOHYDRATES 



The solutions required are as follows : — 



A. Copper solution containing 40 grams of crystallized 

 copper sulphate in i litre of water. 



B. Alkaline tartrate solution containing 200 grams of 

 sodium potassium tartrate, and 1.50 grams of sodium hydroxide 

 in I litre of water. 



C. Ferric sulphate solution containing 50 grams of ferric 

 sulphate, and 200 grams of sulphuric acid in i litre of water. 



D. Potassium permanganate solution containing 5 grams 

 per litre. 



The solution C should not reduce permanganate ; if it 

 does, permanganate solution should be added drop by drop 

 until a faint permanent pink remains. 



Twenty c.c. of the sugar solution to be titrated, which 

 should contain not more than 90 milligrams in that volume, 

 are measured into a conical flask of about 150 c.c. capacity ; 

 20 c.c. each of the solutions A and B are added, and the 

 mixture is boiled for exactly three minutes ; the precipitate 

 is then allowed to settle for a few seconds and is then filtered 

 through an asbestos plug contained in a narrow vertical tube 

 attached to the cork of a filter flask ; the filtrate should be 

 distinctly blue ; the absence of a blue colour indicates that 

 too much sugar has been used and the experiment will have to 

 be repeated, using a diluted sugar solution. The precipitated 

 cuprous oxide should be washed by decantation and finally 

 transferred to the asbestos plug; after throwing away the 

 filtrate and washing out the filter flask, the tube containing 

 the asbestos plug with the cuprous oxide is replaced on the 

 filter flask and 5-20 c.c. of the ferric sulphate solution C are 

 then poured into the original boiling flask to dissolve any 

 adhering cuprous oxide. The resulting solution is poured 

 on to the cuprous oxide on the asbestos pad, and drawn into 

 the filter flask ; after washing out the boiling flask and the 

 asbestos, the combined filtrate and washings in the filter flask 

 are titrated with the permanganate solution D. 



The copper value of the permanganate is determined by 

 accurately standardizing the permanganate solution by means 

 of oxalic acid ; knowing that i gram of KMnOiEE 2-oi grams 



