258 CHEMICAL DISCOVERY AND INVENTION 



permutit mineral is immersed in such water an exchange takes 

 place between the soda of the mineral and the lime and magnesia 

 of the water, resulting in the formation of a solid compound 

 containing the latter bases, in quantity chemically equivalent to 

 the soda removed, while the water retains the harmless sodium 

 carbonate, sulphate, and chloride. After a certain amount of 

 the hard water has passed through the material the latter will 

 naturally cease to act for the obvious reason that it is fully 

 charged with lime or magnesia, and has nothing further to 

 exchange for the earthy constituents of the water. The chemical 

 law of mass action may then be put into operation, by shutting 

 off the hard water and passing slowly a moderately strong solution 

 of common salt in amount considerably in excess of the quantity 

 of soda required to restore the permutit to its original com- 

 position. Under these circumstances the calcium and magnesium 

 pass away in the form of chlorides into the solution. 



After the action is over the filter bed is washed free from the 

 excess of salt and earthy chlorides, and is then ready for its 

 renewed activity as water softener. In practice the softener 

 consists of a cylindrical tank containing a bed of permutit of 

 proper depth (according to the degree of hardness exhibited by 

 the water) arranged between two layers of fine gravel. All the 

 water supply required during the day passes through this bed and 

 issues completely deprived of the hardening constituents. At 

 night the water is turned off and the regenerative salt solution 

 flows slowly through. In the morning the permutit is washed by 

 passing a little water through it, and running the solution of 

 chlorides to the drain. The ordinary water supply can then be 

 resumed. 



The same principle is applied when the purpose is to remove 

 iron which would be objectionable in manufacturing operations. 

 In this case a manganese compound is prepared, and the re- 

 generative liquid is a solution of permanganate. 



CHAPTER XVII 



METALS AND SOME OF THEIR COMPOUNDS 



THE term metal is still in use without the possibility of a strict 

 definition. Seven metals were distinguished by the ancients 

 and were in alchemical times associated in a fantastic manner 



