Before the development of “modern” isotope ratio mass spectrometers (Nier 1947; McKinney et al. 1950) stable isotope ratios and their ratio variations were measured by techniques such as gravimetric determination (e.g. Richards and Wells 1905; Curie 1921) and mass spectrography (Aston 1921, 1931; Kallmann and Lasareff 1932; Nier and Hanson 1936). Although these techniques produced results that were not as precise as the more modern mass spectrometric techniques, surprisingly good results were already obtained with them and the atomic weight of chlorine was determined with good precision using these techniques. Isotope ratio variations in natural samples however were not yet observed using these techniques as natural isotope variations are smaller than the precisions of these techniques. Isotope ratio variations and differences in atomic masses were however observed in samples obtained by separation techniques such as diffusion (e.g. Harkins and Hayes 1921). A short description of these techniques therefore seems viable here as they facilitated the later development of more advanced isotope ratio analysis techniques.