318 PROCEEDINGS OF SECTION B. 
insoluble, and it is precisely at this point that the Von Patera 
process breaks down and the Russell process steps into the aid of 
the metallurgist. 
Mr. E. H. Russell was the first to discover that silver sulphide 
and other compounds which are unaffected by sodium hypo- 
sulphite are soluble in a solution containing in addition cuprous 
hyposulphite, and that a solution of this nature, which he terms 
‘extra solution,” can readily be obtained by adding commercial 
bluestone (copper sulphate) to Von Patera’s solution, which he 
terms “ordinary solution.” It is the practical application of this 
discovery which forms the basis of the Russell process. 
The chemistry of the process naturally falls into six divisions, 
viz. : 
The chloridising roast. 
The preparation and stability of solutions. 
The wash-water. 
The ordinary solution. 
The extra solution. 
Dopo por | 
The precipitation and treatment of precipitates. 
I. THE CHLORIDISING ROAST. 
Although, as has already been stated, the chief. difference 
between the Von Patera and Russell processes lies in the employ- 
ment in the latter of a solution capable of leaching out unoxidised 
silver minerals from ores, and although in one or two instances 
this process has been known to give extractions in the laboratory 
up to 93 per cent. on raw ore, stil], on the score of economy of 
both time and expense, it is generally found preferable to prelude 
the leaching of the ore with a more or less perfect roasting. Of 
all silver compounds, the chloride seems to be the most readily 
attacked by hyposulphite solutions, and therefore this roasting is_ 
almost invariably done with salt in order to convert the metals, 
and especially the silver, into chlorides at the expense of the 
chlorine in the salt rather than into oxides or sulphates. 
As was only natural in a customs mill, the ore treated at River- 
tree during the period under discussion was exceedingly complex 
in character, consisting of a mixture of both oxidised and sulphide 
ores from several distinct lodes. It has already been stated that 
these lodes at a depth consisted of a gangue of quartz in places 
largely replaced by talc, carrying argentiferous pyrites, galena, 
blende, and mispickel. Minute strings of proustite were frequently 
visible, and probably argentite. Near the surface these sulphides 
gave place to the natural products of their decomposition—cerussite, 
calamine, various oxides of iron, and kaolin, derived from the 
decomposed country rock. No metallic silver, or other silver 
