CARBON-14 MEASUREMENTS 423 a rather severe memory effect for CO,. Using ‘C-labeled CO., we have verified that Fergusson’s pretreatment method reduces the memory effect to less than 1%, which is entirely adequate for extended field use of the material. ) EXPERIMENTAL PROCEDURES A photograph of one of the samplers used in this study is shown in Fig. 1. The sieve material is contained in a double-top 1-gal paint can through which air is drawn by means of a suction unit located in the "F “ ae fee woes * ifs ee 2 WHEE ott + Fig. 1—Air sampler used to collect samples of CO; at ground levels.