CHEMICAL EXAMINATION OF ATMOSFHERIC AIR. 221

SECT. II.

CHEMICAL EXAMINATION

OF

ATMOSPHERIC AIR

Chemistry affords two general methods of investigating theconstituent parts of bodies, Analysis and Synthesis ; that bothof these methods can be applied in the investigation of the na-ture of atmospheric air, we shall endeavour to prove.

From some ingenious experiments Lavoisier has demonstratedas stated already, that the air of our atmosphere is not a simplehomogeneous fluid, but consists of two elastic aeriform bodies,possessing very different properties, one of which is capable ofsupporting combustion and animal life, called oxigen gas, andthe other is destructive to animals and extinguishes fire, callednitrogen gas. The atmosphere contains some other gazeousfluids, or bodies capable of being dissolved or suspended in it,but in small quantities. Late experiments seem to have provedthat a minute quantity of carbonic acid is always contained inthe air, for alcalies become effervescent; strontia, barytic, andlime-waters acquire a pellicle on being exposed a sufficient timeto the action of the air, even upon the highest mountains.Water is likewise always found in the atmosphere, but the quan-tity of these matters is extremely minute; and experiments arestill wanting to prove satisfactorily that carbonic acid gas andwater are always and every where present in our atmosphere'