CH. V.] WOOD-OST METHOD. 131 



after a preliminary boiling period of 3 minutes, only a few drops more 

 are required to complete the tit ration. 



With pure glucose solutions the end point is very sharp. With 

 lactose, maltose and diabetic urines the end point is the transition 

 from a green to a yellow colour. 



The special precaution necessary is to ensure that the boiling 

 period is within the stated limits. 



Calculation of results. 



5 cc. of the copper are reduced by 25 mg. glucose. 

 ,, ,, 25 mg. fructose. 



40-4 mg. anhydrous lactose. 



,, ,, 45 mg. anhydrous maltose. 



In the case of glucose the concentration in grams, per cent, is 2-5 divided 

 by volume of solution required. 



160. The Wood-Ost copper carbonate method.* 



Principle. A solution of copper sulphate in carbonate and 

 bicarbonate of potash is boiled with a given volume of the sugar 

 solution. The cuprous oxide formed is filtered off through asbestos 

 and washed with cold water. It is suspended in acid ferric sulphate 

 and the amount of ferrous sulphate formed determined by titration 

 with standard potassium permanganate. The amount of copper 

 reduced being known, the weight of sugar in the volume taken can 

 be determined by reference to a curve or tables. 



Preparation of solutions. 



1. Copper carbonate. Dissolve 250 grams, of potassium carbonate and 

 100 grams, of potassium bicarbonate by the addition of about 600 cc. of warm 

 distilled water. Dissolve 23*5 grams, of pure crystalline copper sulphate in 

 about 200 cc. of water. Gradually add the copper to the carbonate solution, 

 mixing well during the addition. Make the volume up to 1000 cc. and filter. 

 The solution seems to keep indefinitely. 



2. Acid ferric sulphate. Gradually add 250 cc. of pure concentrated 

 sulphuric acid to 750 cc. of distilled water. Add 25 grams, of ferric sulphate. 

 Warm till the sulphate has dissolved, and filter if necessary. The solution 

 must not be used until it has cooled. 



3. Standard potassium permanganate. Dissolve about 6 grams, of potas- 

 sium permanganate in a 1 100 cc. of cold distilled water. Having made certain 

 that the whole has dissolved standardise the solution as follows : Weigh out 

 between 0-3 and 0-4 gram, of pure crystalline ammonium oxalate, determining 



* T. B. Wood and A. Berry, Cambridge Philosophical Journal, xlvi., 

 p. 103 (1904). 



