GASEOUS BODIES. 73 



oxygen gas in the day-time, undoubtedly a design of 

 Providence to renovate the atmosphere, and form a sup- 

 ply for that fixed by respiration and combustion. Oxygen 

 never exists in a separate state, it is always in a gaseous 

 form, or in combination with other substances. 



Nitrogen gas, or Azote, will neither support flame nor 

 animal life. It has neither taste nor smell, and its specific 

 gravity is somewhat less than that of atmospheric air. It 

 may be obtained from atmospheric air, by abstracting 

 its oxygen, which may be effected by burning phosphorus 

 in a jar, inverted over water ; the oxygen will unite with 

 the phosphorus and form phosphoric acid, while the 

 nitrogen will remain. If an equal quantity of iron filings 

 and sulphur be made into a paste with water, and put 

 into a vessel over water, as on the stand of a pneumatic 

 trough, and ajar of common air be inverted over it, in 

 a day or two the mixture will hava imbibed the oxygen, 

 which may be seen by the water rising in the jar, when 

 the remainder will be nitrogen. It may be also obtained 

 from the lean of meat, particularly beef, by pouring over 

 it, in a retort, very diluted nitric acid : the heat of a 

 lamp will disengage the gas, which may be collected over 

 water. Nitrogen, like oxygen, is never in a separate state, 

 but always in combination : it combines with hydrogen, 

 and forms ammonia ; it combines with oxygen in various 

 proportions, and forms different acids, as nitric acid, 

 &c. ; it also enters into several other combinations. 



Carbonic add gas, similar to nitrogen, will neither 

 support life nor flame ; if attempted to be but slightly 

 breathed, it produces so violent a constriction of the 

 glottis as to threaten suffocation ; it is called choke-damp 

 by miners, who are frequently suffocated by it. Its 

 ' specific gravity is considerably greater than that of at- 

 mospheric air, it consequently occupies the lower part of 

 caverns and mines. The Grotto del Cano, a cavern in 

 the kingdom of Naples, has been celebrated for ages for 

 a stratum of this gas covering its bottom ; so that if a 

 dog, or any animal which holds its head down, enters 

 the cavern, it becomes suffocated, while a man will not 

 feel it. In consequence of its weight it may be poured 

 out of one vessel into another ; so that if a taper be placed 



