A MODEL WATER SOFTENER FOR CLASSROOM DEMONSTRATION
A demonstration apparatus illustrating the zeolite or "green sand" process for softening hard water i s described. This demonstration affords a n opportunity, not only to acquaint the student with one of the practical applications of chemistry, but to emphasize the law of mass action. . . . . . . . . . I n the opinion of the writer one of the important objectives of the instructor in high-school chemistry should be to relate the science of class-
room and textbook to the activities of the workaday world. In this particular locality there is a wide range of industries which make use of chemical processes, and classes are cordially received. In some cases, however, where the industry is not of such nature as to necessitate the maintenance of a chemical laboratory, chemical processes are conducted by rule-ofthumb methods and there is little knowledge of the science underlying them. In such cases the instructor must supplement the information acquired by the class in the course of an inspection trip with explanatory details imparted in the classroom. The apparatus here described was devised for such a purpose. 1364
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MODEL WATER SOFTENER
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Construction and Operation The accompanying photograph and drawing reveal aU the essential details of construction. The vessels which serve as containers for salt water (A) and hard water (I?) and for the zeolite filters (E) and (F) are ordinary laboratory acid bottles. The bottoms have been removed from
A-CONTAINERFOR SALTWATER H-4om-WATER DELIVERY B-CONTAINERFOR H A ~ WATRR D 1AND ]-DRAINS EOR WATERWEEN REC AND D-INLETS FOR HARDWATER(AND VIVING SPENTZEOLITE FOR SALT WATER WHEN REGRNERAT- K-DRAM TO SUPPLY HARD WATERPOR ING). TAESE ARE PROTECTEDWITH TEST BRASSSCREEN 1 AND STOPCOCKS E AND F-OUTLET DRAMS POR SOFT WATER
the former two. This may be done by first chilling the bottles and then quickly pouring in enough boiling water to cover the bottoms completely, taking care that i t does not splash upon the sides. When the bottles are lifted the bottoms will drop out. Sharp edges may then be dressed with a file. The zeolite containers are filled to about two-thirds of their volume
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1931
with zeolite. The openings of the tubes (C and D) which serve as inlets into these bottles should be protected with brass screening to prevent clogging. The apparatus shown in the photograph permits switching the flow of hard water from the first softener to the second when the former has "gone hard." However, operation must be suspended when regeneration of one or both softeners becomes necessary. A slight modification in connections (shown in the diagram) makes it possible to revive either softener while the other is in operation. For the reviving fluid we have found i t best to use a saturated brine solution. This is best prepared in advance by allowing concentrated salt solution to stand for several days in contact with excess solid salt. A rapid, easily visible test for hardness is desirable for demonstration use. For this purpose the writer has found soap solution satisfactory. A little hard water &awn a t K curdles the soap; soft water drawn a t H does not. This simple test also serves to indicate the eventual exhaustion of the zeolite and its subsequent revival. The time necessary to complete the exchange of metals which is the essential feature of this process will vary according to the "hardness" of the water and the amount of sand employed. Rates of flow should be adjusted accordingly.
Pedagogical Considerations The instrnctor may employ this demonstration, not only as an explanation of one of the everyday applications of chemistry, but as an occasion for stressing or reviewing the law of mass action and the characteristics of reversible reactions in general.
