JuLy 15. 1892.] 



SCIENCE. 



by the recognition of the products of its decay, but he can 

 by no means assert with certainty that any given water will 

 necessarily give rise to disease or will certainly prove to be 

 wholesome. Waters containing putrescent organic matter 

 of animal origin have been drunk without harmful results. 

 Such cases are on record, and, on the other hand, waters 

 which analysis has shown to be of fair chemical purity have 

 unquestionably given rise to disease. Nevertheless the 

 chemical analysis of drinking waters, despite the limitations 

 and imperfections of our best processes, furnishes most val- 

 uable information, in no other way to be obtained, and I 

 shall spend no time in a defense of this method of investiga- 

 tion. There are unmistakable signs of pollution which 

 analysis may reveal, and such warnings should not go un- 

 heeded. If it be shown that a well receives the leachings of 

 a privy-vault or cesspool, or that a running stream is con- 

 taminated by sewage, as yet unoxidized and possibly in- 

 fectious, such water should be condemned, and neither chem- 

 ist nor bacteriologist should be required to demonstrate its 

 disease-producing power. Indeed this would be in most cases 

 entirely impossible, such proof being seldom attainable. 



Impurities in water exist in suspension or solution, and 

 may be either inorganic or organic. Suspended matter may 

 frequently be removed, wholly or partially, by mere sedi- 

 mentation or by some simple process of filtration, but matter 

 which is held in solution must be destroyed or removed in 

 other ways. The boiling of water may produce a deposition 

 of some of its earthy salts, a coagulation and precipitation 

 of some of its organic matter, and a destruction of its micro- 

 organisms including disease germs if present; and while this 

 method of purification is frequently serviceable as a house- 

 hold measure it is not adapted to use upon a large scale. By 

 distillation a still further purification may be effected, but 

 this is a still more costly process and can never come into 

 general use. Within a few days I have examined a sample 

 of distilled water prepared and sold in bottles for table use, 

 in which, while the free ammonia was high, the albuminoid 

 ammonia was very low; chlorine, nitrites, and nitrates ab- 

 sent, and total solids almost nil. Such water is as pure as 

 can well be made on a commercial scale, but it is necessarily 

 too expensive to be commonly used. Aeration has likewise 

 been resorted to for the destruction by oxidation of organic 

 matter, and is said to have been employed more than a cen- 

 tury ago by Lind on the west coast of Africa. Considerable 

 improvement has been effected in certain city supplies by 

 pumping air into the mains or reservoirs or by discharging 

 water in jets or fountains into basins so as freely to expose 

 it to the air. Where waters are shown to be deficient in dis- 

 solved oxygen, especially in the case of impounded waters in 

 which patches of green algae appear upon the surface in 

 warm weather, such treatment is often of the greatest value. 

 It is an imitation of a natural process of purification, and the 

 change effected is not to be regarded as purely chemical, 

 being brought about by bacterial organisms, the nitrifying 

 bacteria, which, under favorable conditions and in presence 

 of free oxygen, convert nitrogenous organic matter into 

 harmless inorganic forms. 



The purification of polluted water by direct chemical treat- 

 ment has been e%cted with more or less success in many 

 ways, all practical jjc^e.thods involving the separation of pre- 

 cipitated matter eithe^r }}y sedimentat^n or filtration after 

 treatment of the water, ip other words, there is no chemical 

 agent which, by simple addition toimpi^|re watef, will render 

 such water pure and who}p§>^^B. By cjhejnical tpeairuept we 

 may precipitate lime and Oft?,?;' earthjr gg.|J,| jf Present jn 



undue quantity, coagulate and remove organic matter and'' 

 bacteria, or promote the oxidation of such matter; and various 

 processes accomplishing, more or less perfectly, these results, 

 have, during recent years, been employed. 



Clark's process, designed particularly for the softening of 

 water owing its hardness to bi-carbonate of lime, consists in 

 the addition of milk of lime, which results in the formation 

 of an insoluble carbonate subsequently separated by sedimen- 

 tation. Colored and turbid waters are clarified and organic 

 matter and living organisms largely reduced by this treat- 

 ment, as has been shown by Dr. Percy F. Frankland {Chem- 

 ical News, Vol. Lii., p. 40) and others, but if much organic 

 matter is present the precipitation does not readily occur and; 

 filtration must be resorted to as in the Porter-Clark process. 

 Other methods for softening water involve the use of caustic 

 soda in addition to slaked lime, as in Howatson's process, and 

 the use of tri-sodic phosphate, now a commercial article, by 

 which means the salts produciug permanent hardness are 

 largely removed; and in the household carbonate of soda 

 (washing soda) is employed for the same purpose, though 

 its use is impracticable on a large scale on account of the 

 expense. 



Such methods as these, however, are primarily intended', 

 for purifying water for laundry use, manufacturing pur- 

 poses, and making steam. They are more important from a. 

 technical than from a sanitary standpoint, and we pass from 

 these to speak of those processes in which the main object is 

 the removal of constituents believed to be harmful to health. 

 Before doing so, however, a few words concerning filtration 

 may not be out of place, the more especially as either sed- . 

 imentation or filtration is generally necessarily connected 

 with every process intended for the purification of water^ 

 Filtration which is a mere straining, as for example, continu- 

 ous filtration through sand or animal charcoal, may clarify 

 a water without otherwise improving it in any respect, and 

 if, after a time, the filter becomes foul, the water may be- 

 polluted rather than improved. I regard with disfavor most 

 of the old-fashioned filtering appliances, which not only 

 gave a false sense of security, but often served as breeding 

 places for the growth of living organisms. A house filter 

 which is not easily cleansed is an abomination, being gen- 

 erally allowed to take care of itself and in time becoming a 

 source of real danger. A few years ago a case of no little 

 interest was reported in the Chemical News (Vol. LU., p. 70)> 

 Two samples of water were analyzed for a family in which 

 one member was ill with typhoid fever. One of the samples- 

 was from the house supply direct, and the other was the- 

 same water filtered through a portable charcoal filter of the 

 common type. This latter sample yielded a much larger 

 amount of albuminoid ammonia than the former, decolor- 

 ized five times as much pern)anganate of potassium, and was 

 in every respect objectionable. On inquiry it was learned, 

 that the filter had been in use for more than a year, and that 

 in the place where the owner had formerly resided he had 

 found the water so bad that he had made use of it to filter 

 that which he used for his bath. A few years ago whea 

 typhoid fever prevailed in Providence, R.I., and seemed not 

 to be fairly attributable to the city water-supply, Dr. T. M. 

 Prudden examined several of the filters used in private 

 houses and found the typhoid bacillus in no less than three 

 of them {Netv York Medical Joui-nal, Vol. L., p. 14'. Fil- 

 ters giving such results, it need scarcely be said, are a con- 

 stant menace to health, but those which allow of easy clean- 

 ing by reversed cwrrents of water are free from most of the- 

 objections attending Jhe use of the older forms. Five years 



