490 RECAPITULATION. 



Perhaps the truth of this observation is no where more manifest 

 than with respect to the bodies composed of oxygen and nitrogen. 

 These elements constitute the air that we breathe, and also one of 

 the most powerful of the acids ; they give us two other acids scarcely 

 inferior to the other in energy, but possessed of peculiar and charac- 

 teristic properties ; they produce also a gas eminently deadly, and 

 which, by acquiring more oxygen, passes instantly to the condition of 

 one, or of the other of these acids ; and finally another gas, deadly 

 to animals that are confined in it, but which, when breathed for a 

 short time, by human beings, is exhilirating beyond any other agent. 

 These differences, which have been fully unfolded in the preceding 

 pages, are attributable solely, so far as we know, to difference of 

 proportion and to different degrees of condensation. 



2. Dr. Henry, Gay-Lussac, Dalton, Davy and Thomson, have 

 contributed the most important facts, from which have been deduced 

 the proportions, both by volume and weight, of the compounds of 

 oxygen and nitrogen. Gay-Lussac gave us the law, to which no 

 certain exception has yet been ascertained ; "that compounds, whose 

 elements are gaseous, are constituted either of equal volumes of those 

 elements, or that, if one of the elements exceeds the other, the ex- 

 cess is by some simple multiple of its volume," 



It is obvious that if gases sustain this relation by volume, they must 

 sustain a similar one by weight, for twice, thrice, &LC. the volume 

 must be also twice, thrice, &c. the weight ; the temperature and 

 pressure being the same. 



3. The following numerical statements exhibit the proportions of 

 oxygen and nitrogen by volume and by weight. 



By weight Rep. No. Rep. 



for 100 Equivalent of the No. of 



Measures of By weight. parts, proportions, elements, the 



nit. ox. nit. ox. nit. ox. nil. ox. nit. ox. cornp's 

 Nitrous oxide contains 100 50 100-f 57 63.5836.42 +1 14-j- 8 22 

 Nitric oxide, 100 100 100 114 46.68 53.40 2 14 16 30 



Hypo-nitrous acid, 100 150 100 171 36.81 63.20 3 14 24 38 



Nitrous acid, 100 200 100 228 30.40 69.60 4 14 32 46 



Nitric acid, 100 250 100 285 25.97 74.03 5 14 40 54 



It will be perceived that the smallest number in the first, second, fourth 

 and fifth tables, is a divisor of all the larger numbers in that column, 

 and that those other numbers are of course multiples of the smallest 

 number. Most chemists regard common air as a mixture rather than 

 a compound ; but the fact that it corresponds with definite propor- 

 tions, both in volume and in weight, is perhaps the strongest argument 

 that it is a compound and not a mixture, and perhaps no good reason 

 can be assigned why it should not be added to the acknowledged 

 compounds of oxygen and nitrogen. See p. 197-8. 



