1906-7.] Precipitated Sulphur. 309 
1. In the product of the interaction of hydrogen sulphide and sulphur- 
ous acid in aqueous solution the proportion of insoluble sulphur was very 
variable. In one instance it reached 82’6 per cent. 
2. The addition of acids to solutions of calcium or sodium poly- 
sulphides gave sulphur which was almost wholly soluble. Thus, with 
excess of acetic acid all the sulphur was soluble; with excess of half- 
concentrated hydrochloric acid (6 N) less than 1 per cent, was insoluble ; 
with excess of concentrated hydrochloric acid (12 N) 2 '4 per cent, only was 
insoluble. 
The precipitates, viewed through a polarising microscope, were found 
to be composed at first of fluid droplets. The droplets could be seen to 
crystallise, each forming a spherical group of radiating crystals. Later, 
the cluster suddenly resolved itself into a single crystal, without altering 
its spherical shape. This observation of the production of liquid sulphur 
at the ordinary temperature, and its transformation into monoclinic 
sulphur, and finally into spheres of rhombic sulphur (the only stable form), 
was most instructive. 
3. The actions of bromine and iodine upon solutions of sodium sul- 
phide and polysulphide were studied in some detail. When equivalent 
and excessive amounts of the halogens were used, the proportions of in- 
soluble sulphur varied from 8 per cent, to 56 per cent. Bromine gave the 
larger proportions. 
4. The most detailed investigation was given to the action of acids upon 
sodium thiosulphate. The following were the results of some typical pre- 
liminary experiments. In each experiment 100 c.c. of thiosulphate solution 
was used. The concentration of this solution is given in the first column. 
In the second column appears the amount and concentration of the acid. 
In experiment 3 the thiosulphate was added to the acid, in the others the 
acid was added to the thiosulphate. The last column shows the per cent, 
of insoluble sulphur : — 
Concen. 
Na 2 S 2 0 3 
Acid. 
Per cent. Am S 
1 
(100 c.c.). 
4 N 
50 c.c., 12 N. HC1 
340 
2 
4N 
50 c.c., 6 N. HC1 
6-5 
3 
8 N 
500 c.c., 12 N. HC1 
96-0 
4 
4 N 
25 c.c., 16 N. HN0 3 
56*5 
5 
4 N 
300 c.c., glac. HA 
o-o 
Some of the conclusions from these results were : — 
(1) That, whereas Berthelot held that “ positive ” sulphur (as in S 2 C1 2 ), 
when liberated, gave insoluble sulphur, and “ negative ” sulphur (as in 
