1921.] Donovan.—Thornhill’s Sodium-sulphide Process. 133 
It would appear that a solution 4 per cent. Na 2 S, 2 per cent. NaOH 
would be more effective than one containing 4 per cent. Na 2 S, 1 per cent. 
NaOH. This point, and an equally important one, the change of rate of 
solution of HgS as the strength and proportionate composition of the 
solution are varied, still remain to be investigated. 
Another effect of the addition of NaOH is to stabilize the sodium 
sulphide. Bloxham ( Journal Chemical Society , vol. 77, p. 762) states that 
normal sulphide in solution becomes a mixed solution of hydrosulphide 
(NaHS) and hydroxide (NaOH), but that the hydrosulphide does not 
so dissociate. It is at once evident that the addition of hydroxide to 
sodium sulphide will limit this dissociation. Also, the rate at which a 
solution of 4 per cent. Na 2 S will oxidize in air is sensibly retarded by the 
addition of NaOH 1 per cent. 
NaOH has thus three effects : (1) It dissolves the double sulphide of 
mercury and sodium ; (2) it sets free sodium sulphide to combine with 
the mercuric sulphide, and form the double salt, which without it would 
be required to hold the double salt in solution and hence lessen the amount 
of sodium sulphide required ; (3) it stabilizes the solution, and renders it 
less liable to oxidation. 
To return now to the process. There is no difficulty in dissolving the 
cinnabar in the solution recommended—4 per cent. Na 2 S, 1 per cent. NaOH 
—and the maximum amount of mercuric sulphide which can be dissolved 
is approximately 5 per cent, of the weight of the solution taken. In 
practice, however, 50 lb. of solution to 1 lb. sulphide would be advisable. 
To recover the mercury, Thornhill used scrap aluminium, sodium sulphide 
being formed, and alumina precipitated along with the mercury, at the 
expense of the caustic soda present. Theoretically 1 lb. aluminium would 
precipitate 11*1 lb. mercury. The efficiency of this method was not 
investigated, owing to the price of aluminium. An alternative method 
devised was to subject the solution to electrolysis, using a mercury kathode, 
and an anode of gas-carbon or graphite. If the voltage is kept below 3, 
and the current-density less than 0-05 ampere per square centimetre, the 
mercury in solution is deposited in the kathode and the equivalent amount 
of sulphur liberated at the anode with practically no decomposition of the 
sodium salts. The recovery of the mercury is complete, and the solution 
can be used again for treatment of concentrates. 
Cost of Process. 
The suggested process consists of three principal operations—crushing 
and oil concentration, solution of the concentrates, and precipitation of 
the mercury. 
Crushing and Concentration. —The ore is soft, and would be readily 
ground in a Marcy mill to pass 100-mesh, especially if used in conjunction 
with a Dorr classifier, to return coarse particles to the mill. The cost 
of crushing 54 tons per day from rock-breaker size to pass 100-mesh is 
quoted in Mineral Industry, vol. 27, p. 791, as 19-78 cents per ton at 
the Elko Prince Mill, including repairs. I would not, however, estimate 
it at less than 10s. per ton under local conditions and at the present time. 
Oil Flotation. —For this part of the process oil-flotation cells and plant 
for dewatering and partly drying the concentrate would be required. 
Costs at Arizona Smelting Company are given as slightly over 1 dollar per 
ton, including flotation royalty (Megraw, The Flotation Process, p. 228). 
I consider that 15s. per ton would be a fairer estimate locally. This 
would make £1 5s. per ton for crushing and concentration. 
Solution of the Concentrates. —This would require solution-vat, agitation- 
vat, leaching-vat, sumps for solution, and pumps, &c., but would present 
