mated by disappearance of radioactivity from medium) presumably as the resultant of an exchange reaction with potassium a t certain sites of the external surface. Typical results obtained after 16-24 hours of rotary shaking a t 22-25' (at which time R b uptake is near maximal) are shown in Table I. I n the absence of a competing ion orthoclase prefers R b to Na by a factor of about 4:l. However, R b uptake is not significantly diminished by the presence of 10 times more Na (or Li) than R b ; similar R b uptake values are obtained with Na:Rb mixtures a t 30:1, but K in equimolar amounts inhibits R b uptake. NaZ2 uptake cannot be detected in the presence of Rb. TABLE I 2 g. orthoclase (20-80 mesh) incubated for 24 hr. with 2 ml. medium. Medium
RbWl NaZ2C1 RbW1 NaCl NaWl RbCl
+ +
3799
COMMUNICATIONS TO THE EDITOR
July 20, 1959
Concen. uM./ml:
2 2 2 20 2 20
RbsBuptake uM. per 2 g.
Na" uptake uM. per 2 g.
2.06 0.44
2.00
