Considerable attention has been focussed in recent years upon the validity of the radiocarbon dating method by papers whose authors have considered that one or other of the fundamental principles might either be in error or require serious modification (Crowe, 1958; Milojčić, 1957; Elsasser, Ney, and Winkler, 1957; Daniel, 1959). It has even been suggested that errors as great as 800 years might arise between datings on the same sample made in different laboratories (Crowe, 1958). In the light of such criticism, it is clearly of the utmost importance to investigate, and, if possible, justify the basic assumptions on which the validity of the method rests.

In the Copenhagen I and II date lists radiocarbon dates for samples representing the late-glacial Aller⊘d oscillation and early Neolithic periods in Switzerland and Denmark were given. At the time of publication no account was taken of the dilution of the atmosphere with inactive carbon by the extensive combustion of fossil fuels since the Industrial Revolution (Suess, 1955), and of its influence on the dating results. This effect as measured by Suess amounted to 3.4% depletion in wood samples from the heavily industrialized east coast of the United States. Several later measurements have shown that the magnitude of this reduction in atmospheric C14 concentration varies in different areas. The average universal decrease was calculated by Fergusson (1958) as 2.03 ± .15%. However, the magnitude of reported Suess effects may vary with the chosen reference sample as a result of periodic changes (de Vries effect) in the atmospheric C14 concentration as found by de Vries (1958).

The following list includes samples from sites or sections described in archaeologic or geologic publications. Several others, already dated, will be published when the archaeologic and geologic investigations are concluded.

The second series of radiocarbon measurements made at the British Museum Research Laboratory are reported in the following list. The equipment and method used remain the same as described in our first date list (Barker and Mackey, 1959) and, as stated there, the error terms are not based solely on counting statistics but are widened to include contributions of ±80 years for possible isotopic fractionation effects and ±100 years for the de Vries-effect. Ages are calculated on a half-life of 5568 ± 30 years.

The following is a list of radiocarbon dates obtained since the time of the preparation of Michigan list IV. The method of measurement and treatment of data are the same as those described in the introductions to lists III and IV.

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 of bis to their number. One of these (Y-140 bis) was a new preparation of CO2 from 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 C13 analyses have been reported (Oana and Deevey, 1960), are not included here but will form the subject of a separate paper.

The dates given have been obtained during the year 1959. They have been made with carbon dioxide at 2 atmospheres pressure in a proportional gas-counter, as for the series given in Radiocarbon Supplement, volume 1.

This paper is a list of radiocarbon dates obtained at the University of Saskatchewan since the last report was issued (McCallum, 1955). The method used is essentially that of Suess (1954), in which the sample is counted as acetylene gas. The proportional counter has a sensitive volume of one liter and is filled with acetylene to a pressure of one atmosphere. Each sample is counted for at least two 20-hour periods. The modern standards used were obtained from softwood logs grown in Northern Saskatchewan and were either 50 or 100 years old as obtained from ring counts.

This date list covers the period from September 1958 to December 1959 and a few earlier dates omitted from our first list (Nydal, 1959). As regards the geologic samples, the accordance between the C14 age and the age predicted from geologic considerations is generally very good, and most of the discrepancies can be reconciled in favor of the C14 result.

The samples in this list were measured by the methane proportional counter method reported by Burke and Meinschein (1955). Shell samples were mechanically cleaned and washed with water. Where necessary, cold, very dilute HCI was used to remove the powdery exterior. Sedimentary wood and mud or clay samples were treated with hot concentrated HCI and washed with water before burning. Four other types of materials recovered from sediments were dated: (1) the total organic carbon, (2) benzene-soluble organic material, (3) foraminiferal tests, and (4) “dispersed carbonate”. The foraminiferal samples were recovered from the sediment by washing on a 120-mesh screen. These were then converted to carbon dioxide by acid treatment. “Dispersed carbonate” was recovered in the form of CO2, by acid (HCI) treatment of the sediment wash which had been depleted of Foraminifera. The total organic carbon samples were recovered by combustion to CO2 after all carbonates had been removed by acid treatment. Organic extractables were also converted to CO2 by combustion.

The following list covers the samples measured at the Uppsala radiocarbon laboratory during 1959.

The dates listed herein have been determined at the U. S. Geological Survey radiocarbon laboratory at Washington since our last date list (USGS IV) and up to the end of 1959. Acetylene continues to be the gas of our choice. Each sample is run for a period of two days in two separate counters with separate electronics. The modern standard used is wood grown in the 19th century, and the ages and errors have been computed in the same manner as before. Pretreatment of wood, charcoal, and peat samples by boiling in acid, alkali, and acid again, is standard procedure.

This paper is a direct continuation of the second date list released from this laboratory (Östlund, 1959), and the technique of preparation and the characteristics of our two 3-atmospheres carbon dioxide counters are substantially unchanged (Östlund 1957a, b). As in previous lists, our standard is oak wood, grown, A. D. 1845–1855 in Stockholm. corrected for radioactive decay to 1960. As usual, the counting rates have been corrected according to the massspectrometrically measured C13/C12 ratio in each sample of purified carbon dioxide. In this scale the U. S. National Bureau of Standards Natural Radiocarbon Standard (NBS standard) gives a counting rate which is 104.5 ± 0.4% of our age-corrected oak standard. Taking into account that our oak has a C13/C12 ratio of 25 per mil lower than the Chicago PDB-C13 standard, our age figures can, by subtracting 55 years, be converted to the new, international radiocarbon age scale proposed by Broecker and Olson (1959).

The recently established low-level radiation laboratory of Scripps Institution of Oceanography has been measuring radiocarbon since August 1957. Through 1959 about 160 samples have been measured.