GO 
PROFESSOR R. THRELFALL AND MR. J. H. D. BREARLEY 
purification adopted. Berthelot attempts to classify the varieties of sulphur on 
electro-chemical principles. According to him, sulphur exists in two principal 
modifications, one, electro-positive sulphur, liberated at the positive-electrode during 
the electrolysis of chloride of sulphur ; the other electro-negative sulphur liberated at 
the negative electrode during the electrolysis of metallic sulphides. 
The electro-positive sulphur comprises all those varieties which are amorphous ; the 
electro-negative all those which are crystalline. The distinction between crystalline 
and amorphous sulphur appears to us to be much more fundamental than between 
those varieties which are soluble and those which are insoluble in carbon bisulphide. 
Indeed, as is well known, mere crystallization from carbon bisulphide often involves 
the formation of insoluble sulphur. The distinction between the main varieties is 
considerable from the dynamical point of view—for the thermal changes involved in 
passing from one to the other are very great—as was shown by Brodie in a simple 
experiment and by Petersen in an elaborate thermo-chemical research. 
We have chiefly examined those varieties of sulphur which are sufficiently 
definite and permanent to enable us to be sure that we are dealing with pure 
substances. Thus we have examined the monoclinic variety of sulphur pretty 
thoroughly, together with what we believe we are the first to recognize as a new 
variety of monoclinic sulphur, as well as several mixtures of this variety with 
amorphous sulphur obtained by cooling rapidly from a high temperature. The 
permanence of monoclinic sulphur we find to be much greater than is generally 
supposed, at least, if the melting point may be taken as a criterion, # while as for 
octahedral sulphur, the only possible means at our disposal for obtaining it pure— 
viz., by the method of Gernez —-has hitherto failed in our hands. This method is 
based on the obtaining of sulphur in a state of “ surfusion.” The sulphur, which 
is perfectly crystalline to begin with, is melted below 130° C., cooled to, say, 101 3 C., 
and then caused to crystallize in the octahedral form by sprinkling the sulphur with 
a trace of the dust of octahedral crystals. This appears to be a matter of some 
delicacy, and in the course of a good many trials we have not succeeded to our 
satisfaction, even when following M. Gernez’s instructions most minutely. The fact 
is, that melted sulphur has a very strong tendency to crystallize in the monoclinic 
form, and this tendency can only be overcome under the most favourable circumstances 
(if at all) and by the exercise of great care. For most electrical experiments, however, 
it is necessary to obtain a film of the material between two conducting plates 
which serve as electrodes, and the conditions attending the production of such films 
are experimentally unfavourable to forced octahedral crystallization. Again, both 
Foussereau (‘ C.R.’ 97, p. 996) and Boltzmann, Romich and Fajdiga, and Nowak 
(‘ Sitzungsber. der Wiener Akad.,’ vols. 68 and 70) found no appreciable conductivity 
in crystals of octahedral sulphur, though their methods were not very searching. 
* The phenomena attending the transformation of monoclinic into octahedral sulphur will be dealt 
with during the discussion of special cases. 
