Refractions of Atoms and Ions

Atom refractions are known from direct measurement only for monatomic gases. Ramaswamy and Watson (1936), using data obtained by Damkohler (1934) and the Cuthbertsons (1932), deduced Rm s for the rare gases as He 0-52, Ne 1-03, A 4-14, Kr 6-27, and Xe 10-14 cm3. Mercury vapour has been studied by Ladenburg and Wolfsohn (1930-2) and by Wiisthoff (1936) the R value indicated (12-7-13-0 cm3) is close to that given by Evans et al. (1935) for combined mercury (12-84 cm3). 

The data quoted are based upon the earlier estimates by Fajans and Joos (1924). Modifications suggested by subsequent work (e.g. Newman (1934), finding 9-05 cm3 for sodium chloride at infinite dilution in water 

Wasastjerna (1922) found the molecular refractions of hydrochloric, nitric, and sulphuric acids at infinite dilution in water to be 8-45, 10-43, and 13-42 cm3. He assumed that the refractivity of the proton—a nucleus without an electron—was zero, so that the R s just quoted were the refractions of the anions Cl-, NOif, and SO these, subtracted from the Rs values observed for the corresponding salts, gave refractions attributable to the cations involved, e.g. 

Heydweiller (1925) proceeded similarly. The mean estimates from many such operations are in Table 12 under W. and H. 

A more recent treatment of the subject is that of Bottcher (1946), who argued that while the proton undoubtedly has a negligible refractivity it can penetrate a water molecule to give an H30+ ion having a smaller refractivity than H20, so that apparently H+ carries a negative refractivity (compare Table 13). Bottcher therefore started with the 

---