The temporarily exhausted " Permutit " can be readily " regenerated " or " revivified," and so restored to its full activity. To accomplish this it is needful to replace the sodium which it has lost in the softening process. This is easily obtained from a solution of ordinary salt (sodium chloride). When a salt solution is allowed simply to flow through the exhausted " Permutit," the laws of chemical exchange again come into play-the interchange in this case being in the opposite direction- sodium from the salt solution driving out calcium and magnesium from the " Permutit," the latter being at the end of the regeneration process completely re-converted from " Calcium - Magnesium - Per -mutit " into active " Sodium-Per-mutit,', having restored to it the whole of its sodium base, and consequently its full softening power. It is then ready to be employed again in the treatment of a further quantity of hard water, and so on, ad infinitum.

The chemical action which takes place in the regeneration of the " Permutit " Filter is expressed by the formulae given below. It should be noted that neither in softening nor regeneration is any solid deposit formed.

Elimination of Calcium from Exhausted " Permutit."

Ca - Pm + 2 Na CI = Na2 - Pm + Ca CI2 Calcium ;Sodium _ Sodium Calcium

Permutit + Chloride ~~ Permutit + Chloride

Elimination of Magnesium from Exhausted " Permutit."

Mg - Pm + 2 Na CI = Na2 - Pm + Mg CI2 Magnesium Sodium Sodium Magnesium Permutit + Chloride = Permutit + Chloride

Instructions for working " Permutit" Water Softening Plant.-Fig.

219 : normal working position- valves A and Bopen; all othersshut.

Preparation Of Salt Solution

The required amount of salt should be laid on the gauze-lined compartment, and the salt tank filled with the required amount of water.

Before injecting the salt solution into the plant, open valve " T " and steam valve " G," and circulate the solution until all the salt is dissolved. Then shut valves G " and "T."