184 Br. Thomas Thomsons Observations 



exceeded 79 volumes, the least residue being 79*. In six 

 of them, the residue was less than 80 volumes, while in four 

 it exceeded 80 volumes. The mean of the whole, which 

 must be very near the truth, gives 100 volumes of air com- 

 posed of 



Oxygen gas . . . 20-0665 

 Azotic gas . . . . 79-9335 



100-0000 



This only differs by jfa part from 20 volumes of oxygen gas 

 and 80 volumes of azotic gas. While the analysis of air, by 

 means of hydrogen gas, when the hydrogen amounts to 42 

 volumes, and the air to 100 gives the composition exactly 

 20 volumes oxygen gas. 

 80 volumes azotic gas. 

 These experiments, I conceive, leave no doubt whatever 

 that the real constitution of air, freed from all traces of car- 

 bonic acid, is 20 volumes oxygen and 80 volumes azotic gas. 

 But if this be the constitution of air, and if its specific 

 gravity be unity, it is easy to deduce the specific gravity of 

 oxygen gas and azotic gas. Let the atom of oxygen = 1 

 and that of azotic = 1-75. 



Since air is a compound of 1 atom oxygen and 2 atoms 

 azote, it consists in weight of 



Oxygen 1- or 22-222 = a 

 Azote . 3-5 or 77-777 = b 



100 

 Let x = specific gravity of oxygen gas, and 

 y = specific gravity of azotic gas. 



* + 4y . „ 



5 =1. Hence x = 5 — 4 y. 



x:±y::a:b. Hence x=^¥ 



b 



5_4 ?/ = 4 «# , 56 



J nr and 3/=4^T46 = ' 9722 



* = 5-4y = 5-3-888 = Mill. 



Thus, it appears that the specific gravity of pure dry oxy- 

 gen gas is 1 • 1 1 1 1 , and that of azotic gas 0-9722. 



Let us see how near the different experimenters who at- 



