CHAPTER XVII. 



SULPHUR, PHOSPHORUS AND ARSENIC. 



SULPHUR is an element that has been known from the earliest 

 times, as it is found in great quantities in volcanic regions, 

 especially in those of Southern Europe. It occurs as hydrogen 

 sulphide in mineral waters. It forms compounds with several 

 metals, as the bisulphide of iron, sulphide of iron and copper, 

 sulphide of lead, zinc, antimony and mercury. It also is a con- 

 stituent of numerous sulphates, as the sulphates of lime, baryta, 

 strontia, magnesia and soda. It is also found in small quanti- 

 ties in animals and some plants. 



Sulphur is a yellow brittle solid. It melts at 239 F. to 

 a thin straw-colored liquid; when heated to a higher temper- 

 ature it becomes darker in color, and at 350 F. becomes a 

 dark viscid body. At this point the temperature remains 

 stationary for some time, although heat is applied continu- 

 ously, showing that heat is doing other work besides raising 

 temperature. As it begins to rise in temperature again it 

 becomes liquid at about 500 F., and at 836 F. it boils, form- 

 ing a brownish-yellow vapor, which burns in oxygen or in the 

 air with a bluish flame. When a liquid at about 500, if poured 

 into water, it becomes a dark plastic mass much like india rub- 

 ber, but this form is not permanent it soon changes back to the 

 yellow brittle form. 



The plastic sulphur not only differs from brittle sulphur in 

 physical properties but it differs in chemical properties as well, 

 for brittle sulphur dissolves readily in bisulphide of carbon while 

 the plastic form is entirely insoluble ; and further, they differ in 

 their electrical relations, the plastic form is electro-positive while 

 the other is electro-negative. 



The diamond crystallizes in the form of an octahedron and 



(137) 



