Mr Foster , Estimation of Copper. 
91 
solution, the atmosphere of C0 2 preventing oxidation of the 
ferrous salt formed. Moreover the double carbonate of copper 
and potassium is employed instead of the tartrate. 
A solution of copper sulphate was estimated first, and then a 
sample of electrolytic copper was analysed. With both of these, 
when sugar was the reducing agent, satisfactory results were 
obtained. An attempt was next made to estimate the copper 
in a copper coin, and in various mixtures of metals containing 
copper, but in these the results obtained were not so satisfactory. 
The probable causes of the discrepancies will be discussed in 
connection with the series of experiments in which they were 
observed. 
Estimation of copper in copper sulphate. 
Grape Sugar as Reducing Agent. 
I. The solution contained 12‘8760 gms. of the re-crystallised 
salt in 500 c.c. 
For the titration 20 c.c. of the copper solution was taken, and 
15 c.c. of the solution of K^CCb, KEC0 3 sufficed to give a solution 
which was permanent on boiling. 
The reduction was effected by grape sugar, a 10 °/ 0 solution 
being used in this instance, and the quantity added was con- 
siderably in excess of that required for complete reduction of the 
copper. 
Results : — 
(1) 20-47 c.c. of KMn0 4 sol. (5) 20-47 c.c. of KMn0 4 sol. 
(2) 20-32 „ „ ( 6 ) 20-46 „ 
(3) 20-47 „ „ (7) 20-50 „ 
(4) 20-47 „ 
90 
1 c.c. KMii0 4 sol. — 9 Q.J 5 x '90316 KMn0 4 . 
A mean of 20 - 47 c.c. gave 99‘62°/ 0 of the theoretical weight of 
copper present. 
[The copper sulphate employed above was found afterwards to 
contain a trace of iron.] 
The precipitate of Cu 2 0 was easy to filter and to wash free 
from the brown liquid which formed during the reduction. 
II. The solution used contained 13-1595 gms. CuS0 4 , 5H.,0 
in 500 c.c. 
20 c.c. of the solution was taken and 
20 c.c. K 0 CO 3 KHCO 3 sol. added, and 
7 c.c. of grape sugar (10 gms. in 500 c.c.). 
20 
1 c.c. KMn0 4 sol. = x -00316 gm. KMn0 4 . 
