EXAMINATION OF COMMON SUBSTANCES 107 



piece of the sulphur, solidified in this manner, is taken out of the 

 water and examined, it is found to be like caoutchouc ; it can be pulled 

 about like chewing gum, and it is quite as elastic. This springy 

 material is plastic sulphur. But if plastic sulphur be left to itself for 

 a day or two it gradually changes back into octahedral sulphur, another 

 reason for regarding the octahedral as the stable form of the element. 

 In this process of reconversion there is no change of weight. 



FIG. 83. Crystals of prismatic sulphur. 



Effects of heat upon sulphur. Sulphur undergoes a series of 

 changes as it is heated. To follow the changes satisfactorily the 

 heating must be very gradual. When powdered roll-sulphur is heated 

 in a large test-tube it first melts, at about 114 C., into an amber- 

 coloured liquid, which when poured into cold water solidifies into 

 ordinary yellow sulphur. In continuing to heat the melted sulphur 

 above 114 C., however, it gradually gets darker and darker in colour, 

 becoming thicker and thicker in consistency, until at about 250 C. 

 it is so viscid that the tube containing it can be inverted and the liquid 

 will not flow. But if the temperature be still further raised, the thick 

 liquid becomes mobile again, and by and by, at 440 C., it boils, changing 

 into a dark orange-red vapour. The vapour, by sudden cooling, can 

 be changed into a yellow solid, known as " flowers of sulphur." If 

 the boiling sulphur be poured into cold water it is converted into plastic 

 sulphur. 



