OX THE ELECTRICAL PROPERTIES OF PURE SULPHUR, 
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Section II. 
The Preparation and Testing of Samples of Sulphur. 
The earliest note we have found on the influence of minute traces of impurity on the 
properties of sulphur is by Mitscherlich in the •'Journal fur Praktisclie Chemie ’ foi¬ 
ls 56, vol. 67, p. 369. This chemist states that the discoloration of sulphur which 
has been heated to the boiling-point is to be traced to the presence of organic 
compounds. One three-thousandth part of “grease” will produce a very deep red 
coloration in sulphur which has been heated to the boiling-point, and even the 
greasiness produced by handling is said to notably affect the colour of sulphur. The 
strongly coloured organic compound does not come over when the sulphur is distilled, 
and its presence may be detected on the bottom of the retort, where it forms black 
spots. Mitscherlich considers the supposed coloured varieties of sulphur discovered 
by Magnus (‘Ann. de Chim. et de Phvs.,’ [3], vol. 47, p. 194) to be merely sulphur 
contaminated by organic matter : he gives, however, no account of his experiments. 
Monckman (‘ Proc. Roy. Soc.,’ 1889, vol. 46, p. 136) noted the black spots which are 
left in a retort from which sulphur has been distilled, and considers they are produced 
only when the retort is heated by the bare flame—a process leading, of course, to 
the heating of the glass much above the boiling-point of the sulphur. Berthelot 
{ loc . cit.) is inclined to agree with Mitscherlich as to the influence of smali organic 
impurities on the colour of sulphur. 
Stas (‘ Recherches.—Bull, de 1’Academie Royale de Belgique,’ 2eme se'rie, vol. 10, 
p. 253) made use of the vapour of “ pure ” sulphur, but gives no details as to how it 
was obtained. We know of no discussion as to the minute purification of sulphur 
except the one contained in Monckman’s paper—in which he refers to a method 
proposed by one of us, and carries out that method and several others in a very 
careful manner. We must therefore consider the purification of sulphur from the 
commencement, since there is practically no previous work to help us—-we have, in 
fact, to solve the problem of purifying sulphur and of recognizing it in the state of 
purity. Our experiments lead to the following result. 
Pure sulphur can be recognized chiefly by its negative characteristics. It evaporates 
from a platinum basin without residue, it has little or no smell, it has a clear yellow 
colour even when suddenly cooled from above 180° 0. by water; it gives oft’ no gas 
when heated in vacuo, it leaves no black spots when distilled from a retort with or 
without the bare flame; it has a specific resistance of above 1 0 38 C.G.S. units when 
perfectly crystallized in monoclinic prisms ; it exhibits, to all intents and purposes, 
perfect freedom from “ electric absorption ” when in this state, and it is perfectly 
soluble in carbon bisulphide, forming a solution which is absolutely clear. We will 
now give a short account of how these characteristics were determined. 
The question of the colour of sulphur occupied one of us previous to 1888, and in 
that year, and as a result of a good many trials, it was found that when sulphur is 
