The specific activity of Silicon-32 is measured is near-coastal seawaters using anin situ method for the extraction of dissolved silica. The results are discussed in relation to the input of Si³² at the surfacevia rains, the expected variation in its concentrations due to continental run-off and influx of open ocean surface waters. The experimental results clearly demonstrate the usefulness of Si³² as a tracer for the study of the vertical structure of the ocean in the upper layers, and of seasonal variations in the types of waters entering in the coastal regions.

Analyses of uranium extracted from South Pacific waters by thein-situ extraction method point to a uniform depth independent value of 1·14 ±0 02 for the U²³⁴/U²³⁸ activity ratio. This value is also the same, within one standard deviation, as that determined for the N. Pacific, S. Indian and Atlantic waters.

A rapid method of separation of³²P from³²Si by hydrofluorisation saves considerable amount of time besides being more efficient in the chemical recovery of phosphorus. Similarly, 4π beta counting of³²P activity allows a more accurate estimation of small amounts of this activity. These improvements make it possible to reliably measure amounts of³²Si as low as 0·1 dpm present in about 10 tons of water.

The mercury concentration of all analyzed meteorites (falls) shows an increasing trend with their terrestrial age. Such a trend, in view of the intense Hg pollution of the earth, warrants careful selection of well preserved and well documented specimens for analysis.