FRESH WATER FOR ARID LANDS—JENKINS 295 
In the simplest form of the apparatus, two cation and two anion 
selective membranes form a 38-compartment cell (fig. 4). Each 
chamber initially contains feed water, and the assembly or unit cell is 
immersed in brine. The passage of ions from brine to the less concen- 
trated water in the outer chambers through the appropriate mem- 
LEGEND 
tim 
v4 = Cation permselective membrane 
Zs 
YY 
N = Anion permselective membrane 
SS 
Z = Inert and impervious material 
> 
C-1 A-1 C 
Fic. 4.—Schematic cross section of osmionic unit cell. 
branes is necessarily electrostatically coupled with the simultaneous 
transfer of ions from the center to the outer chambers. 
feverse osmosis——Osmosis involves the passage of water through 
a membrane from a dilute solution to a more concentrated one [35]. 
If enough pressure is applied to the more concentrated solution (more 
than 350 p.s.i. for sea water) then the osmotic flow can be reversed 
and pure water will be forced through the membrane. Results of 
research sponsored by the Office of Saline Water have demonstrated 
492520—59-——20 
