308 
Proceedings of the Royal Society of Edinburgh. [Sess. 
XXXI. — Precipitated Sulphur. By Alexander Smith and 
R. H. Brownlee. 
(Read July 8, 1907. MS. received July 15, 1907.) 
{Abstract.) 
In papers previously read before the Society, the behaviour of sulphur 
when heated has been the subject of investigation. It has been shown 
that the transition from a pale-yellow mobile liquid to a deep-brown 
viscous one, which occurs as the temperature rises in the neighbourhood 
of 160°, is due to the production from the mobile sulphur (S A ) of another 
distinct variety (S^). The proportion of the viscous variety (S M ) is about 
4 per cent, at the melting point (114’5°). At 160° it has become 11 per cent., 
at 170° 19 per cent., and at the boiling point 34 per cent. The complete 
succession of changes is as follows : — 
Brh - ' ^ S raonoc r ^ )“' S va p 0r . 
When the boiling sulphur is allowed to cool very slowly all these changes 
take place in the reverse order, and only crystalline, rhombic sulphur is ob- 
tained. When, however, the boiling sulphur is chilled suddenly, there is no 
time for the transformation of the S M into S A , which alone crystallises, and 
hence the cooled mass is plastic. The amorphous sulphur which the plastic 
mass contains is the supercooled S M . Certain catalytic agents affect the 
speed of the change from to S A . Thus, if a few bubbles of ammonia are 
passed into the boiling sulphur, the reversion to S A is greatly accelerated, 
and no (amorphous sulphur) is found in the chilled product. The mass 
after standing for a short time is wholly crystalline. On the other hand, 
sulphur dioxide, which sulphur acquires by exposure to the air, is a retard- 
ing catalyser, and its presence permits the supercooling of the when 
ordinary sulphur is employed. Other substances, such as hydrogen chloride 
and the halogens, have an effect similar to that of sulphur dioxide. Since 
sulphur precipitated at the ordinary temperature contains in many cases a 
large proportion of amorphous sulphur, this investigation was undertaken 
in order to ascertain the exact circumstances under which a variety of 
sulphur which is stable only at high temperatures can thus be formed at 
low temperatures. 
In this work four actions by which sulphur is precipitated were used, 
and two of them were investigated in detail. The amorphous sulphur 
was estimated, after the precipitate had hardened, by extraction of the 
soluble sulphur with carbon disulphide. 
