1921.] Donovan.—Thornhill’s Sodium-sulphide Process. 
131 
This is the first time to my knowledge that oil concentration has been 
successfully applied to cinnabar in New Zealand. It is to be hoped that 
Mr. Morgan will publish full details of the experiments. 
By a single treatment a concentrate assaying 30 per cent, mercury and 
containing 85 to 90 per cent, of the total cinnabar is readily obtained. 
By a double treatment, using a “ rougher ” and a “ cleaner ” cell, this 
result could no doubt be further improved. 
The concentrate as obtained is suited for treatment by the Thornhill 
process, though the solvent action is not as rapid as has been found for 
cinnabar in California. There it was reported that a half-hour contact was 
sufficient for complete solution, but with the Puhipuhi concentrates the 
time required was two to three hours with agitation or forty-eight hours 
without. The process, as mentioned before, consists in dissolving the 
cinnabar in a solution containing 4 per cent, sodium sulphide and 1 per 
cent, caustic soda. It has been known that mercuric sulphide is soluble 
in sodium sulphide, with the probable formation of a double sulphide of 
mercury and sodium (HgS.Na 2 S). To examine this point further, and 
to ascertain the reason for the addition of caustic soda, varying known 
amounts of caustic soda were added to a fixed amount (16 c.c.) of a 
normal solution of sodium sulphide, and a 5-per-cent, solution of mercuric 
chloride run in from a burette until the precipitate formed just failed to 
redissolve— i.e., until the solution was saturated with mercuric sulphide 
formed by the interaction of the sodium sulphide and mercuric chloride. 
The following table, in which the mercuric chloride added is calculated 
to normal strength, gives the results, together with the molecular pro¬ 
portions of mercuric sulphide, sodium sulphide, and caustic soda in each 
solution at the equilibrium point:— 
— 
N.Na 2 S 
taken. 
N.NaOH added. 
N.HgCl 2 
required. 
Proportions of HgS, Na 2 S, and NaOH 
in Equilibrium. 
c.c. 
c.c. 
c.c. 
1 
16 
Ni] 
2-67 
HgS.Na 2 S 
4.0 Na 2 S. 
2 
16 
8 
4-25 
HgS.Na.>S 
1-8 Na 2 S 
1-85 NaOIl. 
3 
16 
25 
5*30 
HgS.Na 9 S 
1*0 Na 2 S 
4*7 NaOH. 
4 
16 
62-5 
6-00 
HgS.Na 2 S 
0 66 Na 2 S 
10‘4 NaOH. 
5 
16 
125 
6-60 
HgS.Na^S 
0 - 4 Na 2 S 
19-0 NaOH. 
6 
16 
300 
7-40 
• • 
7 
16 
Excess of saturated 
8-00 
HgS.Na.jS 
-- 
excess NaOH. 
solution 
The compound formed is probably HgS.Na 2 S, and this is soluble 
in a solution containing four equivalents of sodium sulphide, or in a 
great excess of caustic soda, or in solutions containing both of these 
chemicals. 
The effect of the addition of caustic soda is made very plain if these 
results are plotted in the form of a curve allowing for the sulphide used 
up in changing Hg01 2 to HgS, and converting the Hg01 2 into its equivalent 
of HgS. As Na 2 S may be regarded as NaHS.NaOH (less H 2 0), some 
results are included which were obtained by the titration of NaHS con¬ 
taining small amounts of NaOH, and all the initial solutions are regarded 
as additions of NaOH to 8 c.c. of N.NaHS. 
It will be noticed that the solubility of the mercuric sulphide is 
increased by the addition of the caustic soda, and that the rate of increase 
