268 RECENTLY DISCOVERED GASES. 



able to confirm Berthelot's results with benzine or carbon bisulfid. I 

 bave, however, ottered to place a liter of argon at tbe disposal of my 

 distinguished colleague, that be may repeat bis experiments on a larger 

 scale. No one can doubt tbat it is exceedingly desirable tbat tbe ques- 

 tion of tbese atomic weigbts sbould be finally decided, and that by 

 chemical methods. 



In order that tbe subject may not depend wholly on physical theories, 

 I have considered it from another standpoint. If we assume, as from 

 countless chemical facts we are fully justified in doing, that the periodic 

 law is true, then, giving helium the atomic weight 2 and argon 20, there 

 is no possible place for an element of their mean atomic weight; for, 

 unless we absolutely overturn the accepted views, there is no vacancy 

 in the table for such an element. This appears from the following 

 portion of the table: 



H = l He = 2(f) Li=7 Gl = 9.2 B = ll = 12 N = 14 = 16 

 F = 19 A = 20(?) 



It is true there is space enough between He = 2 and Li = 7, but it is 

 highly improbable that an element belonging to the argon series could 

 have so low an atomic weight. The difference between adjacent mem- 

 bers of tbe same group of elements is generally from 16 to 18 units, but 

 here such a difference is wholly excluded. If, on the other hand, we 

 assume He = 4 and A = 40, it would be, in my opinion, by no means 

 improbable that such an element could exist whose atomic weight 

 would be somewhere about 16 units greater than that of helium, and 

 consequently 20 units less than that of argon. The discovery of such 

 an element would be, therefore, not only a proof of the correctness of 

 40 as the atomic weight of argon, but also a confirmation of the present 

 views regarding the significance of the specific heats of gases for their 

 molecular weight. 



A glance at the periodic table will make tbese considerations clear, 

 tor in the latter case we have the following series: 



Li=7 Gl=9.2 B = ll 0=12 N=14 

 Na=23 Mg=24.3 Al=27 Si=28 P=31 



He=4 

 = 16 F=19 (!)=20 

 S=32 01=35.5 A=40 



Shortly after the discovery of helium I began the search for this 

 suspected element of atomic weight of about 20, at first in connection 

 with Doctor Collie, my former assistant, and later with my present 

 assistant, Doctor Travers. 



At first it appeared not improbable that this element might be found 

 in those uranium minerals from which helium had been obtained. We 

 did not, bowever, confine ourselves to these minerals, but tested all 

 available metals, either by beating in a vacuum or by fusion with sodium 

 bisulpbate. In many of these minerals helium was found; in many, on 



