Procedures and equipment of the laboratory have been described in previous date lists. Wood, charcoal, and peat samples are pretreated with dilute NaOH and dilute H3PO4 before conversion to the counting gas methane; marls and lake cores are treated with acid only. Very calcareous materials are treated with HCl instead of H3PO4.

UCR I (R, 1974, v 16, p 395–401) previously reported measurements carried out jointly by the UCR and UCLA radiocarbon laboratories between November 1972 and September 1973 and interlaboratory check samples used to calibrate the UCR 1.7L counter. This list reports the measurements of the UCR laboratory from September 1973 to August 1974.

The following radiocarbon measurements made since our last date list (R, v 17, p 112–120), are a partial list of projects and samples released for publication by the submitters. The technique employed is liquid scintillation counting of wholly synthesized benzene as described by Noakes et al (1965) and discussed in R, v 16, p 402–408. Errors are reported as one standard deviation. No correction factors are applied.

The Water Resources Division of the US Geological Survey has operated a low-level tritium laboratory since the late 1950's. In 1970, 14C-measuring facilities were added to that laboratory to provide analyses of ground water and other carbonates, primarily for research and field projects of the Division.

The following list contains dates of samples measured since our previous list (R, 1973, v 15, p 435–441). As before, age calculations are based on the Libby half-life 5568 ± 30 yr, and reported in years before 1950. The modern standard is 0.950 of the activity of NBS oxalic acid.

Measurements have continued with the same proportional counter system, pretreatment procedure, methane preparation and measurement, and calculation, as described previously (R, 1970, v 12, p 298–318). Uncertainties quoted are single standard deviations originating from standard, sample, background counting rates and half-life. No C13/C12 ratios were measured.

The following list of dates are selected from geologic and archaeologic samples measured in late 1974. The technique employed is liquid scintillation counting of wholly synthesized benzene as described in (R, v 16, p 402–408). Errors are reported as one standard deviation. Sample descriptions and comments were written in collaboration with collectors and submitters.