The Efficiency of Quenching Collisions and the Radius of the Excited Mercury Atom

The evidence in favor and against the assumption of Foote that every collision of a foreign gas molecule with an excited mercury atom is efficient in quenching the resonance radiation is discussed, and a new calculation of the efficiency of collisions is given, based on Stuart's measurements, which shows that the efficiency can be assumed to be equal to one in the case of CO, ${\mathrm{H}}_2$, and perhaps ${\mathrm{O}}_2$, but that it is undoubtedly smaller than one for ${\mathrm{H}}_2$O, ${\mathrm{N}}_2$, A, and He. CO has actually a greater quenching efficiency than ${\mathrm{H}}_2$. The radius of the excited mercury atom is calculated using an improved value for the amount of resonance-radiation re-absorbed in the resonance vessel and found to be $r_{{\mathrm{Hg}}^{\prime }}=2.91\mathrm{}\times {10}^{-8\mathrm{}}$ cm, or 1.62 times larger than the radius of the normal atom for the case of ${\mathrm{H}}_2$, and $r_{{\mathrm{Hg}}^{\prime }}=5.5\mathrm{}\times {10}^{-8\mathrm{}}$ cm or three-fold normal for the case of CO. The apparent higher quenching efficiency of oxygen than hydrogen is explained by the partial oxidation of the mercury vapor and consequent decrease of the density of the last. It is shown that the life of metastable atoms increases with the admission of certain foreign gases into the fluorescence vessel.