NEWS ; APY ,
ume Nave) Volumetric Estimation of Copper and of Lead. 167
- "I have often used this process, and have always found
T H E C Ha E M I C A L N E Ww S. that the end of the io is very difficult to toe, The
brown colour of the sulphide interferes with the observation
 of the blue colour of the solution. Even when there
1s no other metal than copper present, an addition of the
alkaline sulphide gives a precipitate after the blue colour
has entirely disappeared.
Instead of using an excess of ammonia, I have used an
alkaline tartrate dissolved in an excess of caustic soda.
This liquid is the same which, added to a titrated solution
of cupric sulphate, forms Fehling’s solution. It is prepared
 by dissolving 173 grms. of Rochelle salt in 480 c.c.
of caustic soda of specific gravity 1-14, and adding water
to form 1 litre of solution, This alkaline solution is added
to the copper solutions in slight excess of the quantity
sufficient to dissolve the copper to a deep blue-coloured
liquid, and the porcelain dish is heated so that the liquid
is carried to nearly the boiling-point, The titrated solution
 of sodic sulphide is then added until no turbidity is
produced by the addition of one drop.
In this manner of proceeding the blue colour of the
solution is not taken into account. The dark brown colour
which follows the addition of the reagent is the only guide.
The first addition of the alkaline sulphide gives rise to an
ntense black-brown precipitate. As soon as this is formed
‘he liquid in the dish is thoroughly stirred with a glass
rod. This has the effe& of agglomerating the cupric sulohide
 into coarse curds, which settle to the bottom of the
lish, leaving the liquid clear and almost colourless. If
after settling the liquid should not be sufficiently clear, it
should be vigorously stirred again until the desired effe@
's obtained. After every addition of sodic sulphide the
iquid should be thoroughly agitated until it becomes clear,
The degree of turbidity produced is a guide as to the quan.
[ty of reagent to use,
At the beginning the brown cloud is very intense, and
it is useless to await the complete clearing up of the liquid
before adding more of the reagent. Towards the end the
brown cloud is comparatively slight, and the reagent
should be added drop by drop. The liquid in the dish
should be stirred so as to clear it up entirely before adding
a drop of the reagent.
By thorough stirring the sulphide of copper agglomerates
.n thick heavy curds, which settle rapidly, leaving the surface
 of the dish very clean, as seen through the clear
liquid, On this clean white surface the faintest cloudiness
is easily seen, A liquid containing 1 grm. of copper in
30,000 c.c. of solution will give a distin& brown turbidity
hy the addition of one drop of the reagent.
For the volumetric estimation of lead the same process
may be applied. Sulphate of lead is easily dissolved in
the alkaline tartrate solution described. Sulphide of lead
is precipitated in exad&ly the same manner as sulphide of
copper. The end of the readion is equally definite.
As plumbic sulphate is insoluble in alcohol of about
Go per cent, lead can be separated as sulphate from other
metals, and afterwards dissolved in the alkaline tartrate.
Sulphuric acid could also be precipitated as plumbic sulphate,
 and estimated by this process. Other acids which
form insoluble salts with lead could also be estimated in
‘he same way.
Copper can be separated from other metals as sulphocyanate
 (Rivot’s process). The precipitate is heated with
nitric acid and re-dissolved. This solution is afterwards
treated by the alkaline tartrate solution, and copper precipitated
 as sulphide. Copper may also be precipitated as
cuprous oxide by glucose from an alkaline tartrate solution.
 The cuprous oxide may be dissolved in nitric acid,
then alkaline tartrate solution added to obtain a clear blue
solution, from which copper may be separated as cupric
sulphide.” This is applicable to testing glucose and canesugar.

These volumetric processes for copper and lead are
‘ounded on the easy agglomeration of the sulphides of
:hese metals in the alkaline tartrate solution by agitation.
The heavy clots fall to the bottom, leaving the liquid clear.