310 Proceedings of the Royal Society of Edinburgh. [Sess. 
polysulphides) gave soluble sulphur, in point of fact the very same com- 
pound can yield sulphur wholly soluble (exp. 5), or almost wholly insoluble 
(exp. 3). 
(2) That excess of the acid is not required for the production of insoluble 
sulphur in this action (exps. 2 and 4), although such excess greatly increases 
the proportion obtained (exps. 1 and 3). 
(3) That free sulphurous acid does not determine the formation of 
insoluble sulphur : this acid was liberated in large amount in experiment 
5, but all the sulphur was soluble. 
(4) That the order of mixing makes a great difference in the effect ( e.g . 
exp. 3), evidently because when the salt was added to the acid, the latter 
was present in greatest excess from the very beginning of the precipitation. 
(5) That sulphuric acid (experiments not given above) gave smaller 
proportions of insoluble sulphur than did hydrochloric acid. 
(6) That, other things being equal, the higher the temperature of the 
liquids, the smaller was the proportion of amorphous sulphur. For example, 
equal volumes of 2 N. thiosulphate and 10 N. hydrochloric acid, maintained 
before and during mixing at the following temperatures, gave proportions 
of insoluble sulphur appended: 0° (47*1 per cent.), 25° (34*0 per cent.), 40° 
(308 per cent.). 
These preliminary results showed the conditions required to be ful- 
filled in the quantitative final experiments with the same interaction. 
It was necessary to maintain the same concentration of the ingredients 
throughout the process of mixing. This was achieved by arranging to 
use equal volumes in each experiment, and by allowing the liquids to run 
with equal speed into a mixing vessel provided with a mechanical stirring 
apparatus. It was also essential that the liquids should be brought to a 
constant temperature, and that this temperature should be maintained in 
the mixing vessel in spite of thermal effects. Three different temperatures 
were used, namely, 0°, 25°, and 40°, and constancy (± ‘5°) was preserved by 
suitable contrivances. 
The following part of a set of observations at 0° will serve as a sample 
of the results. The first column gives the concentration of the hydro- 
chloric acid used, the second gives the concentration of the acid immediately 
after mixing with an equal volume of thiosulphate solution. The three 
following columns show the percentages of amorphous sulphur from 2 N., 
4 N., and 6 N. thiosulphate solution, respectively. The last column describes 
the appearance of the sulphur immediately after precipitation when 2 N. 
thiosulphate was used : — 
