25 



a longer time is required. At a certain point the crystal becomes 

 opake, and is often broken in pieces at the moment of the change. 

 When in such a crystal this change has either entirely or par- 

 tially taken place, the melting-point will be above 114 0- 5. The 

 minute crystals of sulphur from alcohol, which are so extremely thin 

 that their angles cannot be measured, have this melting-point of 

 1 14*5, which fixes the system to which the crystals belong. The 

 crystals of sulphur from benzole (rectified coal naphtha) melt also at 

 114'5. The crystals from alcohol are very minute, consequently 

 so readily transformed, that they presented anomalies which led me 

 to doubt whether sulphur of both forms did not exist among them. 

 I answered this question by dividing a certain number of carefully 

 selected crystals, and taking the melting-point of the two halves of 

 the same crystal. I found that these melting-points in many cases 

 did not correspond, which would have been the case if the anomalies 

 had arisen from the different nature of the crystals. Sulphur which 

 has been melted at 114 0> 5, and of which the temperature has not 

 been raised above 1 15, remains, on solidification, perfectly transpa- 

 rent for any length of time. Heated beyond this point, it becomes, 

 on cooling, more or less opake. 



When sulphur has been converted by heating for a sufficient 

 length of time, in the manner above mentioned, between 100 and 

 1 14'5, it acquires a fixed melting-point of 1 20 C. This is the melt- 

 ing-point of the oblique prismatic sulphur. If sulphur thus converted 

 be carefully melted so as to raise the temperature as little as possible 

 above the melting-point, no sensible difference will be observed be- 

 tween the point of melting and of solidification. To obtain this fixed 

 melting-point of 1 20, care must be taken that the transformation of 

 the sulphur has been thoroughly effected. If this be not done, it may 

 melt at any point between 1 14 0- 5 and 1 20. If, however, the tempera- 

 ture of the melted sulphur be raised above its melting-point of 120, 

 the point of solidification will be altered, and may lie even below the 

 first melting-point of 114'5*. The point of solidification is in this 

 case not fixed, but depends upon the temperature to which the sul- 



* This has been observed by Person, who states that if sulphur be heated above 

 150 its melting-point is lowered to about 112 or 1 10. He says, that when heated 

 with care, the thermometer will remain constant during crystallization, &i lib . 

 I have not found this correct. Ann. de Chemie, vol. xxi. p. 323. 



