94 
Mr Foster , Estimation of Copper. 
therefore from this that there was here some disturbing factor 
and it was in all probability the zinc. When sugar was employed 
as reducing agent the presence of zinc seemed always to affect the 
result in the direction indicated above. It is possible (and very 
probable) that the zinc forms with the oxidation products of the 
sugar, an insoluble compound which remains behind with the 
Cu 2 0. This being decomposed by the sulphuric acid in the ferric 
sulphate solution, reduces some of the KMn0 4 , thus causing the 
results to be higher than they ought to be. 
II. Copper Coin. NHfJH as Reducing Agent. 
An estimation of the copper in a 1904 halfpenny was also 
made, hydroxylamine hydrochloride being used to reduce. The 
results were fairly consistent as the following numbers show. 
3T40c.c. gives 9T20°/o of Cu, and the amount usually present 
in coinage is 95'5 °/ 0 . It will be seen that the results are here 
about 4 °/o below what is required by the amount of copper actually 
present. 
III. German Silver. Sugar as Reducing Agent. 
A mixture was prepared to resemble German silver. It con- 
tained 4-5586 gms. Cu, T5 gms. Zn, 1 gm. Ni, and a trace of Fe in 
500 c.c. 
Ten titrations gave numbers varying from 28’2 c.c. to 30 - 37 
for 20 c.c. of solution. The amount required by the Cu actually 
present was 28’65 c.c. 
Half the titrations gave values greater than this. We see 
here again probably the influence of the zinc, since grape sugar 
was used to reduce. It should also be pointed out that the 
double carbonate which Ni forms with K 2 C0 3 is one of the least 
stable of these double salts and is readily precipitated on boiling even 
in the presence of considerable excess of K 2 C0 3 , KHC0 3 solution. 
The precipitate moreover is finely divided and pasty so that filtering 
even with the Gooch filter is a slow process, and the washing of 
the precipitate cannot under these circumstances be very satis- 
factory. 
IV. German silver wire. NH/jH as Reducing Agent. 
8’8830 gms. of the wire were dissolved in HN0 3 and made up 
to 500 c.c. The copper was reduced by means of hydroxylamine. 
20 c.c. of the solution required. 
(1) 31-40 c.c. KMn0 4 sol. 
(2) 31-30 „ 
(3) 3T30 ,, „ 
(4) 31-35 c.c. KMn0 4 sol. 
(5) 31-40 „ 
(6) 31-60 „ 
