from which samples were combined for analysis. 
Five plankton samples were analysed in detail for their 
radioisotopic content eleven months after the date of col- 
lection. These included 
Sample No. Stations 
I (Ave 
1g 23,4 5 
a gat 43, 44,45, 46 
IV 50,51,52,53 
V 57,58,59 
The samples were filtered through No. 1 Whatman filter 
papers and the plankton and filtrate fractions dried sepa- 
rately. Gamma spectra were made from both fractions. The 
plankton samples were then wet ashed with concentrated 
nitric acid and hydrogen peroxide and converted to the 
chloride form by evaporating the sample to partial dryness 
repeatedly with hydrochloric acid. The moist salts were 
dissolved in 0.2 N HCl, filtered, and the filtrate passed 
through a cation-exchange column (5 mm x 100 mm) of Dowex 50 
(IS eure Ieee 
Two hundred and fifty mgm or less of the sample in 0.2 N 
HCl solution were passed through the column at a4 rate of 0.2 - 
0.5 ml per minute, then the resin was washed with 50 ml of 
0.2 N HCl. The eluate from the sample and the subsequent 
hydrochloric acid wash contained those ions not adsorbed to 
the resin, 1.e. the anions. These included Zr?95-Nb95 and/or 
