34 
Standard used Icc. = 0‘1 mgm. copper. 
Taken. Found. 
No. 11 20 mgm. per litre... 20’4 mgm. per litre. 
No. 12 10 „ „ 10 „ „ 
No. 13 25 „ „ 24-28 „ 
No. 14 30 „ „ 28—32 ,, 
20 mgm. of copper per litre = 1 ’4 grains per gallon is the 
largest quantity which can be estimated by this method 
when working with 50cc. of the liquid under examination. 
With lead the following results were obtained : — 
Taken. Found. 
No. 15 10 mgm, per litre... 10 mgm. per litre. 
No. 16 12 „ j, 12 — 15 mgm. per litre. 
No. 17 15 ,, „ colour too dark to allow of 
estimation. 
10 mgm. of lead=0'7 grains per gallon, is, therefore, the 
largest quantity which can be estimated by this method 
when working y/ith 50cc. of liquid. 
In making these determinations, I found that the colours of 
the liquids might be compared immediately after the addi- 
tion of sulphuretted hydrogen. The colours did not become 
intensified on standing. 
I also found that it was immaterial whether the standard 
was added before the sulphuretted hydrogen water or vice 
versa. Thus there is no need if the colour of the standard 
be too light, to prepare a fresh standard, as must be done in 
nesslerising. It is only necessary to add another measured 
quantity to the liquid which already contains sulphuretted 
hydrogen. 
The addition of one or two drops of dilute hydrochloric 
or nitric acid in no way affected the accuracy or delicacy of 
the estimation of copper. In the case of lead, a drop of 
hydrochloric acid caused a faint turbidity (especially in 
estimating large qiianities of the metal), which interfered 
materially with the results. If an acid must be added, 
acetic acid is, I think, the best. 
