26 
(2) Solution of ammoniiim ?iifraf6.-=“Made by dissolving 
100 grm. of the salt ill one litre of water, 
(3) Potassium ferrocyanide sokition.---Cont^mmg 1 part 
of the salt in 25 parts of water. 
(4) Two glass cylinders holding rather more than 150cc. 
each, the point equivalent to that volume being marked on 
the glass. They must, of course, both be of the same tint 
and as nearly colourless as possible. 
(5) A burette, marked to ToCC., for the copper solution ; 
a 5cc. pipette for the ammonium nitrate, and a small tube 
to deliver the potassium ferrocyanide in drops. 
The following is the method of analysis Five drops 
of the potassium ferrocyanide are placed in each cylinder, 
and then a mea^sured quantity of tlie neutral solution in 
which the copper is to be determined into one of them (A), 
and both filled up to the mark with distilled water, 5cc. of 
the ammonium nitrate solution added to each and then the 
standard copper solution run gradually into (B), till the 
colours in both cylinders are of the same depth, the liquid 
being well stirred after each addition. The number of 
cubic centimetres used are then read off. Each cubic 
centimetre corresponds to OT mgrm. of copper, from which 
the amount of copper in the solution in question can be 
calculated. 
The solution in which the copper is to be estimated must 
be neutral, for if it contains free acid the latter lessens the 
depth of colour and changes it from a purple brown to an 
earthy brown. If it should be acid it is rendered slightly 
alkaline with ammonia, and the excess of the latter got rid 
of by boiling. The solution must not be alkaline, as the 
brown coloration is soluble in ammonia and decomposed by 
potash ; if it is alkaline from ammonia this is remedied as 
before by boiling it off ; while free potash, should it be pre- 
sent, is neutralized by an acid and the latter by ammonia. 
