The name is absent

282 Science and Human Welfare
some waters lend themselves to softening more cheaply
through the use of exchange zeolites.

By the action of hard waters on certain complex silicates,
both natural and synthetic, an exchange of the calcium and
magnesium for the sodium of the zeolite may be brought
about. These zeolites, when exhausted, are revivified by
passing a strong solution of common salt through them.
After thorough washing, the cycle may be repeated. The
zeolites were used originally as sodium zeolites, and since
calcium and magnesium are basic, the term “base exchange
material” was often applied. Research has now given us a
carbonaceous zeolite, “Zeo-Karb,” which is free of dangerous
silica. When regenerated with sodium chloride it functions
as the early zeolites. When regenerated with dilute acid,
not only the calcium and magnesium, but also the sodium,
may be removed. Used in this manner we have a “Zeo-Karb
H” unit.

With the advent of this zeolite it became possible to re-
place all metallic ions with hydrogen ions, leaving only the
corresponding acids in solution. Now it is obvious that if the
free acids could be absorbed by some insoluble substance
which could be regenerated and operated indefinitely in re-
peated cycles it would be possible to remove the soluble salts
entirely. Such exchangers have now been developed which,
in some respects, even excel the earlier cation exchangers.
Typical of these exchangers is the aliphatic-amine resin,
called “De-acidite.” Now we have a two-step commercial
unit: the first removes all the metallic components and the
second extracts the acids. Deaeration removes practically all
of the carbon dioxide and the effluent from the process
analyzes as H₂O—nearly as free from soluble materials as if
it had been distilled.

Other applications of these exchangers might be the com-

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