relation between the ratio of activities and the ratio of mass before and after leaching. The ratio of the weight of solid remaining after leaching to the original weight was 48 per cent, whereas the ratio of the activity in the leached solid to the total activity of the solid before leaching was 54 per cent. Table 4.2 —X-RAY-DIFFRACTION ANALYSIS OF RADIOACTIVE PARTICLES REMOVED FROM THE DIFFERENTIAL FALL-OUT COLLECTORS Station Compounds present Janet CaCO; (calcite) CaCO;y (artificial calcite) Compounds probably present Remarks Ca(OH), (Portlandite) CaCO, (aragonite) Wilma CaCO, (aragonite) Amount of sample less than 1 mg; identity of compound not certain 540.16 CaCQ, (calcite) Unknown compounds of See Station 540.18 540.18 CaCO, (calcite) Unknown compoundsof The unknown compounds CaCO, (artificial calcite) CaCO, (artificial calcite) Ca(OH), (Portlandite) large lattice spacings large lattice spacings CaCO, (aragonite) remarks of large lattice spacings are not all the same; preliminary determina- NaCl(halite) tions have shown them to be the less common com- pounds; further research is needed to determine their nature 540.13 Ca(OH), (Portlandite) CaCO, (calcite) NaCl (halite) CaCO; (artificial calcite) 540.14 CaCO, (calcite) CaCO, (artificial calcite) MgO (pericilase) $40.09 Unknown compounds of See Station 540,18 CaCO, (aragonite) Amountof sample less large lattice spacings remarks than 1 mg; identity of compound not certain The liquid from the total collector located at Station 540.18 was analyzed to determine the percentage of activity from ions and that from colloids. This analysis was done by ultrafiltration at 38 atm through a cellophane dialyzing membrane with a pore size in the range of 12 to 40 A, It was found that 71 + 3 per cent of the activity was associated with the ionic species and 29 + 4 per cent with the colloids, Since this liquid sample had been previously filtered through Whatman No. 30 paper, someof the colloids remained with the particulate caught by thefilter. 40