440 Royal Society. 



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°'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 

 114°'5, it acquires a fixed melting-point of 120° 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 120°, 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°' 5 and 1 20°. If, however, the tempera- 

 ture of the melted sulphur be raised above its melting-point of 1 20°, 

 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- 

 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 detei'mine 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 



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

 150° its melting-point is lowered to about 1 12° or 1 10°. He says, that when heated 

 with care, the thermometer will remain constant during crystaUization, at 115°. 

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



