_Softening hard water_.--The disadvantages attending the use of hard water either for drinking purposes, steam generation, lavatory purposes, and for many manufacturing purposes, are well known, but as there are several methods of softening waters which are hard in different degrees by different substances, we may be pardoned if we here reproduce, for the convenience of some of our readers, a few passages from the sixth report of the River Pollution Commission, 1874, pages 21 and 201-16, which give some very valuable information on the relative merits of hard and soft waters in domestic and trade uses. "Some of the mineral substances which occur in solution in potable waters communicate to the latter the quality of hardness. Hard water decomposes soap, and cannot be efficiently used for washing. The chief hardening ingredients are salts of lime and magnesia. In the decomposition of soap these salts form curdy and insoluble compounds containing the fatty acids of the soap and the lime and magnesia of the salts. So long as this decomposition goes on the soap is useless as a detergent, and it is only after all the lime and magnesia salts have been decomposed at the expense of the soap, that the latter begins to exert a useful effect. As soon as this is the case, however, the slightest further addition of soap produces a lather when the water is agitated, but this lather is again destroyed by the addition of a further quantity of hard water. Thus the addition of hard water to a solution of soap, or the converse of this operation, causes the production of the insoluble curdy matter before mentioned. These facts render intelligible the process of washing the skin with soap and hard water. The skin is first wetted with the water and then soap is applied; the latter decomposes the hardening salts contained in the small quantity of water with which the skin is covered, and there is then formed a strong solution of soap which penetrates into the pores, and now the lather and impurities which it has imbibed require to be removed from the skin by wiping the lather off with a towel or by rinsing it away with water. In the former case the pores of the skin are left filled with soap solution; in the latter they become clogged with the greasy, curdy matter which results from the action of the hard water upon the soap solution which had previously gained possession of the pores of the cuticle. As the latter process of removing the lather is the one universally adopted, the operation of washing with soap and hard water is analogous to that used by the dyer and calico printer for fixing pigments in calico, woolen, or silk tissues. The pores of the skin are filled with insoluble greasy and curdy salts of the fatty acids contained in the soap, and it is only because the insoluble pigment produced is white, or nearly so, that so repulsive an operation is tolerated. To those, however, who have been