Si) 



OXYGEN. 



Oxygen is an elementary body that cannot be 

 procured in a separate or free state, that is, it cannot 

 be detached from tlie other bodies with which it is 

 always combined. 



Oxygen gas is so called from two Greek words, 

 signifying the generator of acids, because it was 

 considered by Lavoisier as the only acidifying 

 principle. It has been called also piu^e or vital air. 



About one fourth of the atmosphere consists of 

 this gas, and it is essential to respiration and animal 

 life. It is the most powerful and general supporter 

 of combustion ; and by its union with other bodies^ 

 it forms most of the acids. Oxygen gas may be 

 easily procured by several processes. 



1. It is obtained in the greatest purity from 

 oxy-muriate of potash. Put some of this salt into 

 a small glass retort, place the neck under the shelf 

 of the pneumatic trough, and apply the heat of a 

 lamp to the retort. The salts will soon melt and 

 boil, when oxygen gas will come over in great 

 abundance. 



Q.. Black oxide of manganese is usually employed 

 for furnishing this gas, as it affords it at a cheaper 

 rate. Procure an iron retort made for the purpose, 

 fill it with the oxide, fit a conducting tube to it, 

 and place the retort between the bars of a grate 

 which contains a good fire. Keep up the heat 

 until the retort becomes red hot, and the gas will 

 be received in the pneumatic apparatus. Or it 

 may be made from oxide of manganese, put into a 

 ^lass retort, with half its weight of strong sulphuric 



