450 Gooch and Ward — Copper Oxalate in An 



be expected in the case of a precipitate formed by oxalic acid 

 in hot aqueous solutions of neutral copper sulphate or copper 

 nitrate and in amounts in excess of the precipitable minimum. 

 In the experiments of which details are given in Table I, 

 definite portions of a solution of the copper salt were diluted 

 with water to the volume stated, heated to boiling, and treated 

 with crystallized oxalic acid. After standing over night in 

 contact with the solution, the precipitate was collected upon 

 asbestos in a perforated crucible and washed carefully with 

 small amounts of water. The crucible with its contents was 

 placed in a beaker and covered with about 200 cm3 of hot water 

 containing 25 cm3 of dilute sulphuric acid (1 : 4), and approxi- 

 mately N/10 potassium permanganate of known standard was 

 added to coloration. Pure copper sulphate was used for the 

 experiments of A ; and in those of B, copper nitrate, made by 

 dissolving pure electrolytic copper in nitrate acid, evaporating 

 off the excess of acid and dissolving in water, was used. The 

 solutions of these salts were standardized electrolytically by 

 the method of the rotating cathode.* The permanganate used 

 in these and in all succeeding experiments was standardized 

 against N/10 arsenious acid by acting with a measured volume 

 of it upon a known amount of the standard arsenious acid, 

 adding potassium iodide and titrating the excess of the arseni- 

 ous acid in presence of acid potassium carbonate, by iodine 

 also standardized against the arsenious acid, the difference 

 between the arsenious acid taken and the arsenious acid deter- 

 mined by the iodine being the measure of the value of the 

 permanganate. 



Throughout the series of experiments, the error of the 

 determination increases with the dilution. That the errors 

 found in titration actually represent approximately losses in 

 copper, at least for the smaller volumes, is shown by the 

 difference, in two cases, between the result of titration and 

 the electrolytic determination of copper in the filtrates from 

 the precipitated oxalate. For a volume of 10 cm3 , the average 

 error in the titration of the oxalate precipitated, either from 

 the solution of the sulphate or from a solution of the nitrate, 

 is 0-0002 grm. ; for 50 cin3 it is 0-0011 grm.; for 100 cra3 , 0'0053 

 grm. ; for 200 cm3 , 0*0203 grm. For similar concentrations of 

 the copper salt and of the oxalic acid the deficiency in the 

 copper indicated by titration of the precipitated oxalate in- 

 creases more rapidly than the dilution, a fact which suggests 

 some specific action of water, perhaps hydration affecting the 

 solubility or hydrolysis affecting the composition of the copper 

 oxalate. That time and temperature are not essential factors 

 * This Journal, xv, 320, 1903. 



