M. MATERIA MEDICA, THERAPEUTICS, AND HYGIENE. 537 



ter in various localities and at different depths, and these 

 were secured and sealed up with the utmost care, so as to 

 avoid the possibility of the introduction of any additional im- 

 purities. In the case of all the specimens of water obtained 

 within a few miles of the shore, the beam of light revealed 

 more or less impurity, and it was only in the indigo water of 

 the sea (as distinguished from the green) that he found a de- 

 cided reduction of the amount of foreign ingredients. He 

 assures us that the prevalence of one or the other of these 

 tints in sea-water is always expressive of a greater or less 

 degree of purity, as depending upon suspended matter. He 

 advises the use of an experiment similar to that referred to 

 for determining the purity of water of any kind, especially 

 that used for drinking, as, notwithstanding a careful filter- 

 ing through porous paper, and even through a charcoal filter, 

 there may be left in suspension matter almost too fine for 

 detection by the microscope, and yet clearly indicated by the 

 beam of light. 



He stated in his lecture that the purest water that he was 

 able to find was obtained by melting a block of pure ice, 

 but that even this required extreme caution to insure suc- 

 cess. He called attention to the remarkable purity of the 

 water from the chalk districts of England, and remarked that, 

 but for the hardness of the water, or the amount of carbon- 

 ate of lime held in solution, it would be the most desirable 

 for drinking and other purposes. He said, however, that at 

 Canterbury and elsewhere the water is subjected to a special 

 preparation that causes a deposit of the lime. This is ac- 

 complished by adding clear prepared lime-water to the chalk- 

 water, thereby causing a precipitate of carbonate of lime to 

 the bottom of the reservoir. By this means the percentage 

 of this salt in the water is reduced from 17 to 3, leaving a 

 water of extraordinary beauty and purity. 3 A, June 27, 60. 



HAED WATER VeVSUS SOFT. 



The curious proposition has recently been enunciated by 

 Dr. Letheby, of London, that moderately hard water is better 

 suited for drinking than that which is soft. He states that 

 a larger percentage of French .conscripts are rejected from 

 soft-water districts than from neighborhoods supplied with 

 hard water, and also that English towns with water of more 



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