CH. xvii SULPHUR AND ITS COMPOUND 249 



carefully, and directly you see it to be melting note the 

 temperature recorded by the thermometer, that is, the melting 

 point of the sulphur. You will find it to be about 114 C. 



Effects of Heat upon Sulphur. The effect of raising the 

 temperature above the melting point should be also observed, 

 and the following experiments should be carefully performed. 



EXPT. 253. Put some finely powdered sulphur in a test- 

 tube, using sufficient to fill the test-tube to a height of about 

 1^ to 2 inches, and heat very carefully in a small flame. 

 When all has melted pour a little into cold water. Continue 

 heating the remainder until the liquid boils, and again pour a 

 little into cold water. Examine the cooled products. 



If you performed this experiment with care and have observed 

 the tube continuously, you should have found that the sulphur 

 melts, at first, to a clear yellow mobile liquid, which when poured 

 into cold water solidifies to the ordinary yellow sulphur. On 

 further heating, however, the liquid gets much darker and 

 thicker, becoming so viscid that the tube may even be inverted 

 without the liquid running out ; this occurs at a temperature of 

 about 250 C. At higher temperatures still, it again becomes 

 thin and mobile and finally boils, giving off a dark orange-red 

 vapour which condenses to an orange liquid or to a yellow 

 powder, or which burns at the mouth of the tube with a pale 

 blue flame, and the characteristic smell of sulphur dioxide. 



Varieties of Sulphur. The boiling sulphur when suddenly 

 cooled by cold water forms a remarkable product, as it may now 

 be pulled about like a piece of caoutchouc, which indeed it closely 

 resembles in appearance. It is called Plastic Sulphur. 



EXPT. 254. Place the piece of dry plastic sulphur, previously 

 weighed, on one side and examine again after a few days. You 

 will find that it has returned to the ordinary modification, but 

 that its weight is unchanged. 



Hence, plastic sulphur, although so different in its appearance 

 and physical properties, really consists of nothing but sulphur. 



On the surface of the water, into which you poured the boiling 

 sulphur, you will probably have observed a quantity of a very 

 fine yellow powder, and this consists of sulphur which has con- 

 densed directly from the gaseous to the solid state without form- 

 ing the intermediate liquid, and is known as "flowers of 



