140 EXPERIMENT STATION. [Jan. 



VOLUMETRIC DETERMINATION OF COPPER.' 



BY E. B. HOLLAKD, M.SC. 



The co-operation of the laboratory in the experiments con- 

 dncted by other departments of the station has often rendered 

 necessary qnantitative determinations of reducing sugar, sucrose, 

 lactose and starch in a variety of products. The final step in 

 every case is the determination of the cuprous oxide precipi- 

 tated from Allihn's solution by the reducing action of the sugar. 

 After a considerable study of different methods of filtration, 

 and various ways of determining the amount of precipitate as 

 copper, cuprous and cupric oxides, the following method was 

 adopted, having j)roved highly satisfactory if reasonable atten- 

 tion is paid to details. It might be said, further, that as such 

 work often has to be done at odd times, it is desirable to main- 

 tain a supply of sugar tubes,- and only to titrate when there are 

 a number of tests on hand. By exercising a little care the same 

 tubes can be used repeatedly without change of felt. 



The process consists of heating an aliquot part of the sugar 

 solution with the mixed Allihn's solution (30 cubic centimeters 

 of " white," 30 cubic centimeters of ^' blue " and 60 cubic centi- 

 meters of water) and filtering by aid of suction through a sugar 

 tube with an asbestos felt supported by glass wool. The cuprous 

 precipitate is transferred to the tube, washed with hot water 

 until free from alkali and then with alcohol. The copper is 

 dissolved in 5 cubic centimeters of concentrated nitric acid, 

 thoroughly washed with hot water, and the filtrate run into an 

 Erlenmeyer flask by means of suction. The solution is evapo- 

 rated to small volume to expel excess of acid, and afterwards 

 diluted with 00 cubic centimeters of water. Too great concen- 

 tration should be avoided, as it often results in the precipi- 



' An adaptation of the Low zinc-acetate method. 

 - Eimer and Amend, No. 3263. 



