July 15, 1892.] 



SCIENCE. 



37 



gallon was suflScient for the complete precipitation and clari- 

 fication of the New Brunswick city water, if sufficient time 

 was allowed for settling. Such an amount is imperceptible 

 to the taste and can exert no physiological action. If more 

 alum is used less time is required for sedimentatioD, and vice 

 versa. More than two grains to the gallon was seldom re- 

 quired. They showed likewise that waters which will not 

 yield clear filtrates on account of their containing finely di- 

 vided clayey matters, even when filtered through the finest 

 filter-paper, were immediately coagulated and precipitated 

 by 1.16 grains of alum to the gallon, so that they could be 

 filtered immediately after adding the alum, yielding bril- 

 tiantly clear filtrates, and. in their opinion, no more than 

 twice this quantity, or about two grains per gallon at most, 

 need ever be employed. 



In January, 1889, a sample of peaty water from Athol, 

 Mass., having a decided yellowish-brown color, was submitted 

 to me for examination. Difficulty had been experienced in 

 clarifying this water by filtration, and I made some experi- 

 ments to determine the action of alum upon it. Our city 

 supply was at that time yellowish in color and slightly tur- 

 bid, and this was also tested. It was found that, in both 

 cases, the addition of alum in the proportion of 3.3 grains per 

 gallon gave rise at the end of twenty-four hours to a yellowish 

 flocculent deposit, undergoing no further change on standing 

 for four days, the water becoming clear and almost perfectly 

 colorless. The waters were tested again by adding thealum, 

 shaking in a flask, and immediately filtering through paper. 

 The city water became transparent and perfectly colorless, 

 and the peaty water retained but a very faint, almost imper- 

 ceptible yellowish tint. The peaty water yielded originally 

 0.0225 parts of albuminoid ammonia per 100,000, but after 

 the addition of alum, agitation and filtration, it yielded but 

 0.0060 parts, or about one-fourth as much, showing how great 

 an improvement had been effected. 



For household use, on a small scale, water can bs easily 

 clarified and purified by placing a layer of clean cotton, two 

 or three inches deep, at the bottom of a glass percolator, such 

 as is used by druggists, and pouring the water to be filtered, 

 to which solution of alum has been added, into the percolator 

 and allowing it to drip through into a clean vessel placed to 

 receive it. The alum solution is conveniently made by dis- 

 solving half an ounce of alum in a quart of water, and of 

 this solution a scant teaspoonful should be added to each 

 gallon of water to be filtered. Alum is now used in a num- 

 ber of filtering and purifying systems which have of late 

 years been brought prominently before the public by their 

 inventors or the companies controlling them. 



If now it be asked, do such processes as these which we 

 have described, admit of practical and economical application 

 to the purification of large volumes of polluted water for the 

 supply of our great cities, I fear that an unqualified affirma- 

 tive answer can hardly be given. In American cities the 

 consumption of water is much greater than in European 

 towns. The " Encyclopedia Brittanica" states that " the con- 

 sumption varies greatly in different [English] towns, rang- 

 ing from about twelve to fifty gallons per head per day," 

 and that "an ample supply for domestic use and general 

 requirements is from 20 to 25 gallons per head daily."' With 

 us a hundred gallons is frequently supplied. Albany wants 

 15,000,000 gallons, with a population of less than 100,000. 

 Philadelphia and St. Louis consume 70 gallons; New York, 

 80; Boston, 90; Chicago, 115; and Detroit, 150; while Glas- 

 gow, Dublin, and Edinburgh consume but 50; London, 40; 

 Birmingham, Leeds, aud Liverpool about 30; and Manchester 



and Sheffield still less. On the continent it is about the 

 same. Paris uses about 50 gallons; Hamburg and Dresden 

 60, and Leipsic but 23. In American cities the waste of water 

 is enormous and to purify one gallon for drinking and house- 

 hold uses and nine gallons for flushing water-closets, water- 

 ing streets and extinguishing flres must ever be a wasteful 

 process, to say the least. Many towns in this country are 

 now using water purified by artificial means, with apparent 

 satisfaction ; but I do not think that the time has come when 

 it can be said that such purification is practicable in all cases. 

 Certain methods, like the Anderson process, give excellent 

 results under favorable conditions, but competent engineers 

 have not recommended them for American cities. Sedimen- 

 tation, coagulation, filtration, aeration, all these have passed 

 the experimental stage and are in a sense practical, but that 

 processes involving so much manipulation can be advan- 

 tageously employed in treating the enormous volumes of 

 water required by large cities, especially where pumping is 

 also necessary, is not as yet demonstrated. As regards fil- 

 tration alone, it may be said that in our climate the filter- 

 beds, which give satisfactory results in many parts of Europe, 

 cannot generally be employed to advantage, and that this 

 method of filtration has been by no means uniformly suc- 

 cessful even in Europe. In a recent report Dr. Theobald 

 Smith has called attention to the fact that in the Berlin epi- 

 demic of typhoid in 1889, " the distribution of the disease 

 was identical with that of the filtered river water," the filter 

 beds being worked with great rapidity to make up for a de- 

 ficiency in the water-supply, and the filtered water containing 

 at times 4,000 bacteria per cubic centimeter. In discussing 

 this case he says: " These facts go far to prove that polluted 

 water, when immediately delivered for consumption even 

 after filtration, is not wholly safe. They likewise make prom- 

 inent the fact, that, while filtration largely rids a given water 

 of its bacteria, it is a process requiring the utmost care, the 

 most constant attention, not only on the part of the engi- 

 neer, but also of the chemist and bacteriologist. We are 

 furthermore convinced," he adds, "by these experiments 

 that surface water which shows very little, if any, pollution, 

 and which is stored before use, is safer than filtered water 

 which before filtration is being manifestly contaminated with 

 sewage." As regards methods of rapid filtration under 

 pressure, combining chemical treatment of the water, gener- 

 ally by alum, as well, various systems are in use in this 

 country, controlled by individuals or companies employing 

 a variety of patented devices. Granting that the results in 

 some cases seem to be excellent, I think the time has not yet 

 come when they can be unhesitatingly recommended for the 

 purification, in all cases, of large city supplies. I know of 

 no city with a population of one hundred thousand that is 

 using such a process to-day. That numerous infectious dis- 

 eases are conveyed by water admits of no dispute. In my 

 opinion it is vastly better to purify our sewage before dis- 

 charging it into the streams which supply us with water, or 

 keepit out of them if practicable altogether, than to attempt to 

 purify the water which it pollutes. Chemical treatment 

 and filtration may be practicable and efficient in certain 

 cases', but I believe that the statement by the Elvers Pollu- 

 tion Commission of England, more than twenty years ago, 

 in their sixth report, is as true now as it was then : " Noth- 

 ing short of the abandonment of the inexpressibly nasty 

 habit of mixing human excrement with our drinking water 

 can confer upon us immunity from the propagation of epi- 

 demics through the medium of potable water." The cities 

 of this countrv mav eventually be driven to methods of arti- 



