FRESH WATER FOR ARID LANDS—JENKINS 297 
zone is passed along a column of salt water to concentrate the salt 
impurities at one end. This has been done and fresh water actually 
obtained but rates of production are very low; it remains to be deter- 
mined if there is a basis for a practical method. 
Research and development on demineralization by freezing ap- 
pear worthy of great emphasis. Its inherent advantages indicate 
that a freezing process when completely developed should be able to 
compete economically with the most promising developments in the 
distillation field. 
COMPRESSOR f= 
REFRIGERATION UNIT 
Chilled 
Refrigerant 
Compressed 
Vapor | 
FREEZER 
ICE AND 
SEA WATER 
SEPARATOR 
j Fresh Water 
i toHeat 
fExchanger 
Cold Brine t 
_Heat Exchan 
Ice & Brine 25 F—~> 
}Sea Water 
from Heat 
Exchanger 
35°F 
HEAT EXCHANGER 
° 
er 
FREEZE-EVAPORATION PROCESS 
Fic. 5.—Layout of freeze evaporation, by Carrier Corporation. 
OTHER PROCESSES 
Lon exchange.—The phenomenon of ion exchange was investigated 
about 1850 but it is only within the past 20 years that this principle 
has been extensively developed commercially for treating water of 
low salinity and for removal of hardness. 
Salt ions can be removed from saline water by passing the water 
through a mixed bed of ion-exchange material. That material soon 
becomes saturated and must be regenerated by use of relatively 
expensive acids and bases. 
To overcome this excessive cost, a process suggested by Gilliland 
[42] is being developed at the University of California [43], at 
Berkeley, which employes ammonium bicarbonate as a regenerant. 
When saline water is passed through such a bed, it is demineralized 
and the effluent consists of water containing only ammonium bicar- 
bonate. Heating the solution removes the chemical as carbon dioxide 
