Royal Society. 439 



in shallow water. The facts now adduced materially strengthen 

 this inference. 



In the British Museum there is a beautifully spotted example of a 

 Devonian Terebratula, brought by Sir John Richardson from Boreal 

 America. 



Specimens of the Turbo rupestris, from the Lower Silurian Lime- 

 stone of the Chair of Kildare near Dublin, exhibit appearances that 

 seem to indicate spiral bands of colour. 



March 30.— Thomas Bell, Esq., V.P., in the Chair. 

 The following paper was read : — Note on the Melting-point and 

 Transformations of Sulphur." By B. C. Brodie, Esq., F.R.S. 



In the treatises of chemistry where the results of different ob- 

 sen-ers are collected, various statements will be found as to the 

 melting-point of sulphur. The numbers given in Gmelin's Che- 

 mistry vary from 104°-5 C. to 112°-2C., but of live chemists cited, no 

 two agree as to this apparently simple fact. There is evidently 

 some peculiarity about this melting-point which is the cause of these 

 anomalous results. In some experiments on allotropic substances, 

 in which I have been engaged, I had occasion to submit this ques- 

 tion to a more searching inquiry than it had hitherto received, in 

 which I have discovered the cause of these discrepancies. In the 

 present note I will briefly give the results at which I have arrived, 

 reserving the details for a further and more full communication. 



The melting-point of sulphur varies according to its allotropic 

 condition. This condition is readily altered by heat, and invariably, 

 without peculiar precautions, by melting. Hence the temperature 

 at which sulphur melts is different from that at which it will solidify, 

 or at which, having been melted, it will melt again. 



The melting-point of the octohedral sulphur, as crystallized from 

 the bisulphide of carbon, is 114°-5 C. But from the facility with 

 which this sulphur, when heated even below its melting-point, 

 passes into the sulphur of the oblique system, this fact may readily 

 be overlooked. "When this sulphur, in the state of fine powder, is 

 heated even for the shortest time between 100° and 114°-5, this 

 change cannot be avoided. For the transformation of large crystals 

 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 ])lace, the melting-point will be above 114°-5. The 

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

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

 114°-5, which fixes the system to which the crystals belong. The 

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

 I14"-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 



