vii The Atmosphere 103 



this experiment, for the cold glasses immediately condense 

 a blinding film of dew-drops from the air, (b) When a 

 little clear lime-water is shaken in a flask of air the liquid 

 becomes milky from the formation of solid carbonate of 

 lime, a compound of carbonic acid with lime. Hence, 

 carbonic add is one of the constituents of air. (c) When 

 a candle, or a piece of charcoal, or of phosphorus is allowed 

 to burn in a limited quantity of air under a tumbler or bell- 

 jar inverted in water, the flame soon goes out, and another 

 bit of burning charcoal, or phosphorus is extinguished the 

 moment it is introduced ; moreover, the water rises until it 

 fills about one-fifth of the jar, showing that about one-fifth 

 of the atmosphere is a gas which is consumed by burning 

 substances. This gas .is oxygen, (d) The residue from 

 which burning phosphorus has extracted the oxygen is a 

 gas with no striking properties called nitrogen, (e) When 

 a sunbeam traverses a darkened room, or when strong sun- 

 light streams through an opening in a thick cloud, immense 

 multitudes of motes may be seen dancing in the light. 

 Thus dust is an ingredient of the atmosphere. The amount 

 of water-vapour is variable, and the amount of dust is still 

 more uncertain ; but the other constituents occur always 

 very nearly in the proportions : 



Total 100-00 100-00 or i 



152. Nitrogen. The most abundant gas of the atmo- 

 sphere has no colour, no taste, no smell, no tendency to 

 combine with other elements, no poisonous effect on living 

 creatures, and no power to keep them alive. From the 

 last circumstance it is sometimes called Azote. Its service 

 in the atmosphere is mainly to dilute the other ingredients, 

 and to produce mechanical effects. Most of the pressure 

 of the atmosphere, the strength of wind, the refraction of 

 light, and the buffer -action which breaks the force of 

 meteorites and drives them into dust, are due to nitrogen. 



