SULPHUR. 



173 



the warm band the expansion occasioned by the heat causes 

 a separation and friction of the crystals, and consequently 

 a crackling sound. So, also, when the roll is broken the sur- 

 face presents a glistening appearance, because of the multi- 

 tude of surfaces of crystals. Even in the flowers of sulphur, 

 though apparently a fine powder, there is really the crystal- 

 line state, as may be seen by examining the pow- 

 der with a microscope. When a fair opportunity is 

 given to the particles of sulphur to arrange them- 

 selves without disturbance, crystals are formed of 

 considerable size and of great beauty. In the fis- 

 sures and cavities of the beds of sulphur in vol- 

 canic countries there are collections of crystals of Fig> T3 * 

 the shape seen in Fig. 73. It is curious that the crystals 

 are of a different shape if they are formed artifi- 

 cially. Melt some sulphur in a crucible, then, let- 

 ting it stand till a crust forms over the surface, 

 quickly break the crust, and pour out all the sul- 

 phur that is yet liquid. On breaking the cruci- 

 ble afterward you will find the cavity of the 

 sulphur covered with fine crystals in the form 

 of lengthened pillars, as represented in Fig. 74. 

 Sulphur is said, therefore, on account of its taking 

 these two crystalline forms, to be dimorphous, 

 from the Greek dis 9 twice, and morphe, form. 

 Amorphous Sulphur. Twist a wire 

 the mouth of a test-tube, Fig. 75, 

 so that you can conveniently hold it, and, 

 filling the tube with flowers of sulphur, hold 

 it over a Bunsen burner. The sulphur as it 

 melts but half fills the tube. At first it is 

 thin like water, but on heating it more it 

 becomes brown and thick. If now you heat 

 it a little farther it becomes fluid again, Fig. 75. 



Fig. T4. 



235. 

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