782 



Dr. R. v. Hirsch and Mr. F, Soddv : A Gas 



p, 



V. 



p 2 V. 



26 



15000 



10140 



28 



13000 



10192 



32 



10000 



10240 



34 



8000 



9288 



40 



6000 



9600 



26 



5000 



10180 



51 



4000 



10404 





Mean value . 



10292 





Hydrogen va 



lue 38120 



The second indication given by earlier results is the 

 probable connexion of the p 2 V values with the molecular 

 weights. But as this regularity mainly rests on the com- 

 parison of hydrogen and nitrogen, more gases ought to be 

 tested. Unfortunately, the members of the argon family, 

 which seemed best suited for this purpose, show the peculiarity 

 that their behaviour is extremely dependent on very small 

 impurities present (Strutt, Phil. Trans, vol. cxciii. p. 377, 

 1900 ; Soddy, loc. cit.). Helium was tried and gave p 2 Y 

 values much higher than hydrogen. 



Several compound gases were then tried, choosing such 

 bodies, the occurrence of which seemed possible for one 

 reason or another. These gases are : — 



Water vapour, 



Carbon dioxide, 



Methane, 



Acetylene, 



Cyanogen, 



Hydrocyanic acid. 

 None of these gases could stand the discharge without 

 changing ; water vapour, methane and hydrocyanic acid 

 split up into their components, the carbon compounds forming 

 a thin carbon deposit on the glass near the cathode. Acety- 

 lene and cyanogen begin by polymerizing, the latter forming 

 paracyanogen, which is deposited on the cathode, the former 

 probably benzene. On the other hand, a partial decomposition 

 sets in, the equilibrium altering with every change of pressure 

 or potential. Carbon dioxide is less quickly decomposed, 

 but is not stable enough to give satisfactory p 2 Y values. 

 Moreover, it shows an anomaly otherwise not observed, the 

 bulb becoming suddenly non-conducting with a small decrease 

 of pressure, so that no readings could be taken above 5000 volts. 

 On the whole, all these gases were found altogether unlike 

 the unknown gas, and small chance seems to be left to find 

 it among the class of chemically compound bodies. 



