Owing to a little difficulty that presents itself sometimes in de-
termining the end of the reaction, due to differences in tint, a
duplicate assay should go on at the same time, so that if the
first assay was run a little over or a little under the mark, by
a second observation this could be corrected. An example
will make matters clearer.
•5 grm. of a sample of electrotype copper supplied by Messrs.
E
Hopkin and Williams required 80 cc. of — hyposulphite (theo-
retical quantity being 79*2 cc.) and a sample of tube-plate
copper previously completely analyzed by the foregoing
methods and giving gg'So per cent, of copper by difference,

required 79-8 cc. — hyposulphite. Then

80 : 79-8 : : -S : a: = -49875
•49877 X 2 X 100 = 997S per cent, copper present.
Reactions :

2 Cu(N03)2 -f 4 KI = CU2I2 + 4 KNO3 + 12
2 NasS203 + 12 = 2 Nal -f NajSiOe



Analytical Data of a Complete Analysis of a Sample of
Copper by the foregoing Methods.
Residue insoluble in 6 E HNO3.
50 grms. taken.
Grms.
Watch glasses -\- clip -\- filter paper after drying in

water oven for 2 hours 31 '8997

Ditto -j- insoluble residue dried i hour in water oven . 38-9097
„ „ „ „ „ 2nd time 38-9097



Insoluble residue in 50 grms. -0100

•01 X 2 =: 0-02 per cent, insoluble residue.
D



34



METALS, ALLOYS, ETC.
Estimation of Iron, Nickel, &c.
Calculation for amount of sample taken.
Original sample taken := lo grms.
Flask (i) + cork

Do. -|- liquid -|- CuS . ....
Grms.
