1895.] Argon, a new Constituent of the Atmosphere. 271 



was reasonable to suppose, that part afc least of the phlogisticated air 

 of the atmosphere consists of this acid united to phlogiston, yet it 

 was fairly to be doubted whether the whole is of this kind, or 

 whether there are not in reality many different substances com- 

 pounded together by us under the name of phlogisticated air, I 

 therefore made an experiment to determine whether the whole of a 

 given portion of the phlogisticated air of the atmosphere could be 

 reduced to nitrous acid, or whether there was not a part of a different 

 nature to the rest, which would refuse to undergo that change. The 

 foregoing experiments indeed in some measure decided this point, as 

 much the greatest part of the air let up into the tube lost its elas- 

 ticity; yet as some remained unabsorbed it did not appear for certain 

 whether that was of the same nature as the rest or not. For this 

 purpose I diminished a similar mixture of dephlogisticated and 

 common air, in the same manner as before, till it was reduced to a 

 small part of its original bulk. I then, in order to decompound as 

 much as 1 could of the phlogisticated air which remained in the tubs, 

 added some dephlogisticated air to it, and continued the spark until 

 no further diminution took place. Having by these means condensed 

 as much as I could of the phlogisticated air, I let up some solution 

 of liver of sulphur to absorb the dephlogisticated air ; after which 

 only a small bubble of air remained unabsorbed, which certainly was 

 not more than T ^ of the bulk of the phlogisticated air let up into 

 the tube ; so that if there is any part of the phlogisticated ai.v of our 

 atmosphere which differs from the rest, and cannot be reduced to 

 nitrous acid, we may safely conclude that it is not more than xi^th 

 part of the whole." 



Although Cavendish was satisfied with his result, and does not 

 decide whether the small residue was genuine, our experiments about 

 to be related render it not improbable that his residue was really of a 

 different kind from the main bulk of the " phlogisticated air," and 

 contained the gas now called argon. 



Cavendish gives data* from which it is possible to determine 

 the rate of absorption of the mixed gases in his experiment. This 

 was about 1 c.c. per hour, of which two-fifths would be nitrogen. 



III. Methods of Causing Free Nitrogen to Combine. 



To eliminate nitrogen from air, in order to ascertain whether any 

 other gas could be detected, involves the use of some absorbent. The 

 elements which have been found to combine directly with nitrogen 

 are : boron, silicon, titanium, lithium, strontium, barium, magnesium, 

 aluminium, mercury, and, under the influence of an electric discharge, 

 hydrogen in presence of acid, and oxygen in presence of alkali. 



* ' Phil. Trans.,' vol. 78, p. 271, 1788. 



