26 



phur is raised and upon the mode in which it is cooled. It has varied 

 in my experiments from 118 to as low as 111. When the melting- 

 point of the sulphur, thus solidified, is taken, it will begin to melt 

 at about the temperature of solidification. The cause of this ano- 

 maly is evident. When the temperature of sulphur is raised above 

 120, a transformation into the viscid form instantly commences, so 

 that the sulphur is a mixture of the two varieties, and the melting- 

 point varies according to the proportion in which these two varieties 

 are mixed. It varies inversely with the temperature to which the 

 sulphur is raised, so that the presence of the viscid sulphur lowers 

 the point of solidification. There is, however, a limit beyond which 

 the melting-point is not affected by this admixture. I made the 

 experiment of pouring sulphur, heated to its boiling-point, into 

 water of different temperatures, and of taking the melting-point of 

 the sulphur when it had become hard. Five different preparations, 

 which, when extracted with bisulphide of carbon, gave each a differ- 

 ent quantity of insoluble sulphur, coincided in the melting-point of 

 about 112. This sulphur, before melting, becomes transparent, and 

 passes again into the viscid or elastic condition. 



The sulphur which is insoluble in bisulphide of carbon, and which 

 is prepared by extracting the hardened viscid sulphur with that re- 

 agent, has a melting-point considerably above 120, but which I 

 have not been able to determine with precision. 



I had placed in a water-bath, at 100, tubes containing fragments 

 of the three definite varieties of sulphur. After a short time, on 

 examining the tubes, I found the insoluble sulphur, which I have 

 stated to have such a high melting-point, distinctly melted. The 

 octohedral sulphur had become opake and rounded at the edges, the 

 other was unaltered in appearance. Further inquiry convinced me 

 that the cause of the melting of the insoluble sulphur was, that it 

 had passed into another modification, and that this conversion was 

 attended with evolution of heat sufficient to melt the sulphur. The 

 insoluble sulphur thus converted remains transparent, and is per- 

 fectly soluble in bisulphide of carbon. 



It is stated in chemical treatises that the opacity which on solidi- 

 fication comes over the melted sulphur, is due to the transformation 

 of th& oblique prismatic into the octohedral sulphur, and the con- 

 sequent disruption of the crystal. To this cause also is attributed the 



