Page:Popular Science Monthly Volume 92.djvu/272

 Softening Water by Filtering It

For domestic use a water softener is an absolute necessity to prevent waste

��THE production oi absolutely soft water (water of zero hardness) is one of the most notable recent achievements of industrial chemistry. A little more than half a century ago two English chemists, Clark and Porter, discovered that the addition of lime and carbonate of soda would reduce the hard- ness of natural waters. To soften water com- pletely, however, was considered an impossi- bility, save by distilla- tion. Then came Dr. Robert Gans, a chemist in the service of the German Geological Sur- vey, with the discovery that certain substances in the soil, known as zeolites, had the power of absorbing hardness from water brought in contact with them. Since the capacity of natural zeolites to effect this change was found to be too weak for commer- cial use. Dr. Gans set about the production of an artificial zeolite which he called Permutit. His artificial product softens the hardest of natural waters. Fur- thermore it is entirely in- soluble and can be used over and over again.

Permutit is essentially a silicate of sodium and aluminum and when hard water, that is, water containing in solu- tion salts of calcium and magnesium, is passed through a filtering medium of this substance, the sodium in the permutit changes place with the calcium and magnesium, which remain in the filter, thus substituting sodium salts for them

��Water inlet

��Soft

water

outlets

f

��and softening the hardest natural water. Permutit is of a granular and flaky tex- ture, very porous, exceedingly tough and possessing a mother-of-pearl lustre. It is made by fusing in definite proportions the minerals, feldspar, kaolin, pearlash and soda. The fused mass is crushed. After the soluble matter is washed out the mass is ready for use.

Permutit can be regenerated when all of its sodium has been exchanged for calcium magnesium. This is accomplished by allowing a solu- tion of ordinary table salt to stand the filter over

���Crushed marble suppqrted on : screen

��^^Permutit
 * ^ ,on gravel

^Collection ^chamber

��let to sewerfor back sh cleansing water -'

��Above: How the water is softened simply by pass- ing it through a filter filled with permutit

��At right: A filter which supplies thousands of gal- lons of soft water a day for industrial purposes

���night. The calcium and magnesium in the filter are replaced automatically with sodium, and the filter, after a washing of about thirty minutes, is again ready for use. There are filters which have been regenerated nearly three thousand times.

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