196 COMMON SUBSTANCES 



Carbon occurs very commonly in living matter, partic- 

 ularly in vegetable substances. In these cases it is 

 nearly always combined with other elements, usually O 

 and H. The element occurs free in two forms, diamond 

 and graphite. Diamond is the hardest of minerals, and 

 graphite one of the softest ; both are crystalline, and each 

 is nearly pure C. Graphite mixed with clay is used as 

 " black lead " in pencils. 



226. Sulphur. Sulphur is a solid element, brittle, 

 and of a yellow color. It occurs free in the earth, 

 especially near volcanoes ; it also occurs combined with 

 metals in sulphides and sulphates. It burns easily, 

 forming with O a gas, sulphur dioxide (SO 2 ). The com- 

 pounds of sulphur (e.g. FeS 2 , H 2 SO 4 , H 2 S, etc.) are of 

 great importance to man. In its free state, S is used in 

 preparing matches, gunpowder, and rubber goods ; also 

 in medicine. Sulphuric acid (H 2 SO 4 ) is one of the most 

 important of chemical compounds. 



227. Phosphorus. Phosphorus is a solid element, 

 slightly yellow in color, and of a waxy nature at usual 

 temperatures. It is an acid-forming element and occurs 

 largely in phosphates. P is very active, combining with 

 several elements directly and at low degrees of heat. 

 It should always be kept and cut under water. 



Experiment 124. Cut a piece of P no larger than half a small 

 pea. Dry this on blotting paper and place it in an evaporating 

 dish. Place a bit of iodine so as to touch the P. Do you notice 

 anything that is unusual ? 



Caution. Do not touch P with the hands, and do not breathe 

 the fumes from burning P. The substance is very poisonous. 

 Also be careful never to leave the least bit lying around. 



