Dates obtained since our last date list (Yale III∗), and up to the end of 1958, are given here. All are based on duplicate measurements of CO2 in a proportional counter. Grateful acknowledgment is made to the National Science Foundation, which has supported our work through grant no. G-2278. Participation of Väinö Hoffren during 1956–1957 was made possible through an arrangement with the Geological Survey of Finland. The technical assistance of Julius Kovats has been invaluable.
The following list of dates, measured since the publication of Yale IV, includes a few repetitions of published dates, noted as such by the addition ofbisto their number. One of these (Y-140bis) was a new preparation of CO2from a sample previously measured as acetylene; the others are rechecks of repurified CO2, repeated because instrumental difficulties plagued our laboratory throughout the year beginning in September 1958 and might have affected some dates published in Yale IV. No important differences were found, however. Several measurements of geochemical interest, on lake water and other lacustrine materials for which C13analyses have been reported (Oana and Deevey, 1960), are not included here but will form the subject of a separate paper.
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