93 
Mr Foster, Estimation of Copper. 
(1) 
1840 c.c. 
KMn0 4 sol. 
(5) 18-60 cc. KMn0 4 sol. 
(2) 
18-70 „ 
(6) 18-75 „ 
(3) 
18-70 „ 
5J 
(7) 18-50 „ 
(4) 
18-80 „ 
JJ 
(8) 18-70 „ 
Theory requires 
19-38 c.c. 
These results are fairly consistent, but they are about 3°/o 
below what is required for the amount of copper actually present. 
No doubt a small proportion of the Cu 2 0 is dissolved by the 
undecomposed hydroxylamine, or by the ammonia which may be 
set free during the boiling, and as this escapes into the filtrate, 
we have an explanation of the low results. This explanation is 
borne out by the fact that whenever the filtrate was examined in 
cases where the results were lower than they ought to be, copper 
was found in it. 
II. A solution of copper in nitric acid (3T8gms. of Cu in 
500 c.c.) gave, with NH 2 OH as reducer, the following numbers: — 
(1) 
19-00 c.c. KMii 0 4 sol. 
(5) 
19-25 c.c. KMn0 4 sol, 
(2) 
19-10 „ 
(6) 
19-25 „ 
(3) 
19-25 „ 
(7) 
19-10 „ 
(4) 
19-25 „ 
20c.c. of the solution was used. 
1 c.c. KMn0 4 sol. = T 7 r- 7 r x '00316 KMn0 4 . 
199 
19'20c.c. gives 96'54°/ 0 of Cu. 
This is again about 3 °/ 0 below the actual percentage. Copper 
was invariably found iu the filtrate when tested for. 
Application to solutions of copper containing other metals. 
I. Copper. Tin. Zinc. Grape Sugar as Reducing Agent. 
An attempt was now made to estimate the copper in a solution 
containing also tin and zinc. The solution was prepared to re- 
semble closely that which would be obtained by dissolving a 
copper coin. It contained 5‘481 gms. Cu in 500 c.c. 
20 
1 c.c. KMn0 4 sol. = - x 00316 gm. KMn0 4 . 
lyyo 
20 c.c. of the solution required amounts of KMn0 4 solution 
varying from 33'90 c.c. to 36'57 c.c. The amount theoretically 
required was 34-30 c.c. and the quantity of KMn0 4 used ex- 
ceeded this in nearly 7 0 °/ 0 of the titrations. It was clear 
