140 ELEMENTS OF SCIENCE 



Chlorine is a gas of a green colour, and can be com- 

 pressed into a yellow, limpid liquid when subjected to a 

 pressure about four times that of the atmosphere, but 

 rapidly becomes again gaseous when such pressure is 

 removed. Like oxygen, it is a supporter of combustion, 

 and powdered-antimony when thrown into it burns spon- 

 taneously. It possesses a powerful and peculiar odour. 

 Many of its compounds are termed chlorides, and, united 

 with the metal sodium, it forms chloride of sodium, or 

 " common salt." 



Carbon is an element which remains solid even at the 

 highest temperatures yet applied to it, but it is rarely 

 found pure. As such it may exist in one of three different 

 conditions (i) as pure charcoal; (2) as black-lead or 

 graphite ; and (3) as the diamond. It is very abundant 

 united with oxygen. Such oxide of carbon, or carbon 

 "rust," is a gas at all ordinary temperatures and 

 pressures, though by extreme pressure it has been made 

 liquid and also solid. It is commonly known as " carbonic 

 acid," and since it is formed by the union of charcoal 

 with oxygen (six parts, by weight, of carbon to sixteen 

 parts of oxygen), it is given off abundantly where coal fires 

 are burned. It is a colourless gas with little, if any, 

 odour, and a burning candle plunged into it becomes extin- 

 guished. United with a variety of other substances it 

 produces what are known as carbonates, such as carbonate 

 of lime and carbonate of soda. Four equivalents of car- 

 bon, four of oxygen, and two of hydrogen, constitute 

 citric acid, so commonly used for effervescing drinks. 

 This acid will unite with other substances, such as 

 ammonia, potash, soda, and lime, forming a citrate of 

 each respectively. 



Sulphur. This yellow elementary mineral, commonly 

 called " brimstone" is normally a solid ; but a small 



