329 PROCEEDINGS OF SECTION B. 
II, PREPARATION AND STABILITY OF SOLUTIONS. 
There are always at least three different solutions in use on 
a Russell process mill, viz., (a) ordinary solution, (6) extra solution, 
and (c) precipitating solution. 
(a) Ordinary solution is prepared by dissolving crystallised 
sodium hyposulphite in water, the strength recommended for 
general use, which was adopted at Rivertree, being 14 per cent. in 
the crystallised salt, Na,S,O.5H,O. This solution is very per- 
manent under ordinary conditions, and even when heated to 50° C., 
at which temperature it is a much more energetic solvent for 
silver salts, it only oxidises extremely slowly to sulphate. It is 
unaffected by organic matter, and can, therefore, be stored in 
wooden vats. Its action on copper and copper alloys is much more 
rapid than on lead or iron ; hence the lastnamed metal should be 
used for all pipes and taps, whilst india-rubber hose can be used 
for distributing. Owing to the permanency of this solution it 
can be employed over and over again, its strength being brought 
up to standard from time to time by the addition of the neccessary 
quantity of hypo. which can be determined by titration of the 
solution with standard iodine. 
(6) Extra solution consists of a solution of sodium and cuprous 
hyposulphites formed by dissolving blue-stone in ordinary solution. 
The equation for its formation is :— 
13 Na,8,0, + 6 CuSO, = 4 Na,8,0,3 Cu,S,0, + 6 Na,SO, + 
3 Na,8,0,. 
This requires the use of 2°15 parts of sodium hyposulphite to one 
part of bluestone. The standard extra solution in use at Rivertree 
was that recommended by Russell, and contained | per cent. of 
bluestone and 2} per cent. of crystallised sodium hyposulphite. If 
neutral or alkaline, this solution rapidly decomposes with precipi- 
tation of cupric hydrate ; if, however, it be rendered slightly acid 
with sulphuric acid, this decomposition is considerably delayed 
even when the solution is heated to 50° C. It has been found 
best, however, not to attempt to keep this solution in stock, but 
make it as required, by running ordinary solution on to the vats 
through a sieve containing the requisite amount of bluestone. 
(c) Precipitating solution :—NSince silver chloride is readily 
soluble in hyposulphite solutions, evidently the precious metal can- 
not be precipitated in this form from the liquors, neither can it be 
precipitated by copper, owing to this metal dissolving in excess of 
sodium hyposulphite with the formation of extra solution which 
we have seen is an energetic solvent of metallic silver. 
