A discussion of various technical improvements in the tritium analysis facility is presented. A summary is also given of the tritium content of Chicago precipitation from 18 December 1957 to 15 June l959. A smooth decay curve was obtained during an undisturbed period of two months following the "Hardtack" weapons tests in the spring and summer of 1958; a residence time for water in the troposphere of 21.0 plus or minus 1.4 days is reduced therefrom. Examination of the data following cessation of weapons tests reveals a major peak of tritium activity in March 1959; an anomalous peak in June 1959 is noted and discussed as a subject for further study. (auth)