NITROGEN. 197 



(d.) Very great rarefaction diminishes, and even destroys its pow- 

 er of supporting combustion. 



(e.) Great condensation does not increase the intensity of the com- 

 bustion, although it is sustained for a longer time. 



(f.) Mixture with various gases diminishes it.* 



3. COMPOSITION, IN VOLUME, 80 NITROGEN, 20 OXYGEN BY 

 WEIGHT, oxygen 22.22 



nitrogen - - 77.77 



100.00 very nearly. f 



This proportion of oxygen is undoubtedly that which is best adapt- 

 ed to the support and comfort of human life, and to the convenience 

 of all the animal creation. Experiments have proved that animals 

 compelled to breathe oxygen gas alone, soon become feverish from 

 excess of stimulus, and life is eventually destroyed by the intense- 

 ness of its own functions ; just " as a candle burns brighter in oxygen 

 gas, and is more quickly consumed, so in this gas, the flame of life 

 would be more vivid, but sooner burnt out." 



Most chemists have stated the composition of air at 21 per cent, of 

 oxygen. Dr. Henry states that he could never satisfy himself wheth- 

 er it was 20 or 21 ; Dr. Hare obtained very constantly 20.66, but 

 20 corresponds with the theory of volumes, viz. 1 to 4, and also of 

 definite proportions by weight, that is, 1 proportion of oxygen 8, to 

 2 of nitrogen 28. Still the greater number of chemists do not admit 

 that the atmosphere is a chemical compound. 



4. MEANS OF ANALYSIS. 



They are numerous ; every substance which abstracts oxygen with- 

 out returning any thing ^ may be employed for this purpose. 



(a.) Phosphorus is effectual, either by slow or rapid combustion ; 

 the latter is the most convenient process, and if we subtract T \f of 

 the volume on account of the vapor of phosphorus dissolved, in the 

 nitrogen, the result will be accurate. 



(b.) Iron filings and sulphur moistened, and standing in contact 

 with a confined portion of air remove the oxygen.^ 



(c.) Quicksilver heated in the confined air of a retort, forms 

 oxide of mercury. 



(d.) Many other things to be mentioned in their place, produce a 

 similar effect ; see hydrogen, nitric oxide gas, hydro-sulphurets, &c. 



In all these cases, oxygen is abstracted and nitrogen gas is left, and 

 we know of nothing which will remove the latter gas, and leave the 



* See Henry, 10th Lon. Ed. Vol. I, p. 296. 



t Thomson's Principles of Chemistry, Vol. I, p. 100. t Turner. 



If they stand too long, hydrogen may be evolved from the decomposition of 

 water. 



