FOOTS AND MOHLER: IONIZATION 443 



by dissociation into (HgCl)+ and (Cl)~. The ionization poten- 

 tial corresponding to this type of inelastic collision differs by 

 1 . 8 volts from the ionization potential (without dissociation) of 

 mercurous chloride. An ionization potential may exist corre- 

 sponding to the removal of the second chlorine ion from the mer- 

 curous chloride ion, but this type of ionization is statistically 

 improbable in low voltage arcs. This potential would have a 

 value equal to the difference of the complete and partial ioniza- 

 tions, viz., J'ngci, - Jugch = (i2345''-io-s + 8.8 - Jugci) 

 volts. Finally, an ionization potential may exist corresponding 

 to the formation of a mercuric chloride ion. Evidence for this 

 would be the existence of spectra characteristic of HgClo as dis- 

 tinguished from HgCl, but no spectral relations of this type are 

 established. 



Relations analogous to those described for mercuric chloride 

 probably hold for the other chlorides of this group and the halogen 

 compounds. Even though such compounds as ZnCl are incapa- 

 ble of existing to any stable degree there is no apparent reason 

 why they may not exist momentarily as a product of decomposi- 

 tion, and especially so as positive ions. In fact, the existence 

 of ZnCl"^ is recognized in electrolytic dissociation of ZnCl2. 



Lohmeyer^ has studied in some detail the emission spectra 

 of the mercuric halides. Each shows a characteristic com- 

 plicated band structure. This gives further evidence that ioniza- 

 tion of HgXo into Hg++ and 2X~ is at least not predominant, 

 for then, as with the alkali halides, we would expect to find 

 no spectrum characteristic of the salt. Whether the observ^ed 

 spectra rise from the ions (HgX) + or (HgX2) + remains an open 

 question. 



Hydrogen-chloride, -bromide and -iodide. — -The ionization of 

 these gases has been considered by Born, Fajans, and others.^ 

 The thermochemical relations are as follows: 



(HCl) + Ohci = 'MB.,) + V2(Cl2) 



V2(H2) + I^H = (H) 



* Diss. Bonn, 1906. Zeit. Wiss. Phot. 4: 367. 1906. 



^ Series of papers in Verh. d. Phys. Ges. 1919-20. See also FooTE and 

 MoHLER. Journ. Amer. Chem. Soc. September, 1920. 



