Pasteur has demonstrated that oxygen, supplied in the form of pure atmospheric air, is fatal to bacteria and other germs, while Dr. Pehl, of St. Petersburg, in the course of experiments with Neva water, at St. Petersburg, showed that water containing about 50,000 bacteria in a certain volume, after having been passed for about three-quarters of an hour through and through a centrifugal pump, had lost all but about 500 in the same volume of water. It is evident that the air caught up and violently agitated with the water produced the effect, which, however, can be obtained more satisfactorily by aeration at less than one-tenth the cost of centrifugal work, involving an enormous waste of power to pump or spray the water, aeration or air-treatment being understood as forcing the air through the water, by which operation a violent agitation of the water is combined with rapid movement of the air in the most rational and economical manner.

A recent publication speaks of experiments made for the purification of water at Philadelphia, by aeration, as follows: A Fairmount turbine engine was converted into an air pump, which delivered 20 per cent, by volume, of free air into the water main, this being the proportion found necessary to surcharge the water. Analysis showed that the quantity of free oxygen in the aerated water was 17 per cent, greater than before aeration, while the quantity of carbonic acid was 53 per cent, greater and that of the total dissolved gases was 16 per cent, greater.

The aeration of the water supply for Hoboken, N. J., was inaugurated, converting the formerly abominable Hackensack river water, unfit for ordinary domestic purposes, into a clear, sweet, unobjectionable water supply.

At an annual meeting of the American Society of Civil Engineers, a member made an interesting statement relating to the process for the aeration of water as introduced under his observation. He stated that during June of the preceding year an unpleasant taste and smell was first noticed in the public water supply of a city near New York. In July these peculiarities became very pronounced, and then a green scum began to collect on the water in the reservoir. After a while this took the appearance of green paint. There was no unpleasant taste or smell from the water drawn along the force main, and none from the source of supply, but after it was delivered into the reservoir the taste and smell became offensive. Then it was found, by keeping the water in motion from the time it left the river until it was delivered to consumers, these unpleasant characteristics largely disappeared.

Analyses frequently made showed that there was a deficient supply of oxygen in the water, and that the development of green vegetation increased as the supply of oxygen in solution in the water decreased. In its normal condition the amount of oxygen in solution in good water is about 6 1/2 cubic centimeters per quart, 0.65 of 1 per cent, by volume; but in this case it had run down to about 3 1/2 cubic centimeters. There is no sewage pollution in this area. The difficulty was entirely of vegetable origin. Since the deficiency in oxygen, together with a somewhat large percentage of dissolved extractive matters of vegetable origin, were the only abnormal features revealed by chemical analysis, it was suggested by a prominent scientist, whose co-operation had been requested, that the water could be improved by supplying the oxygen requisite to bring the water to its normal condition, and probably succeed in oxidizing the dissolved extractive matters at the same time. By laboratory experiment it was ascertained that the offensive taste and smell which affected certain water could be made to entirely disappear, and this had led to devising a process by which aeration could be easily applied. The benefit of aeration of drinking water has indeed been recognized from time immemorial, and had already been made the subject of certain patents in this country, but these involved the use of air at merely ordinary atmospheric pressure. These patents have been improved upon by introducing the air under greater pressure, which not only causes the work of oxidation to be very rapidly and effectually performed, but makes the process of such a character as to be easily applied in practice.

Under this advice air compressors were set up and the air was forced into the water mains under a pressure of about 125 pounds to the square inch. By so doing, the oxygen in the water is increased, and, ordinarily, when the water is not turbid from suspended earthy matter (a difficulty encountered after heavy storms, and which, of course, can only be completely removed by filtration), it manifests a sparkling appearance, and has only a pleasant taste and smell. The water as drawn from the main is often perfectly white, but in a moment it clears up from the bottom like soda water, and those who take the water directly from the main drink it with delight while still effervescent. Analyses of the water from different points are made once a month and sometimes oftener. Microscopic examinations are made also, which show that the animal life is changed in different conditions of the water. At present the condition of the water seems to be excellent.

Another system of aerating water, differing in many essentials from the foregoing process, and likewise patented, also applied to large water supplies, by which aeration is secured continuously and economically, is by gravity. To give the reader an intelligent idea of this method and its application, the writer will take the liberty of quoting from a very interesting and highly instructive pamphlet on the filtration of water, recently issued by the owners and patentees of this system,* as follows:

"The main feature may be described by taking, for example, a water supply that is pumped from a river or some other source, up to an elevated distributing reservoir. Between the pumps and the filter a stand pipe is raised. The supply pipe may, for convenience, be run through the centre of the stand pipe till within a short distance of the top, or it may be placed in any other position that the peculiar locality of the water supply calls for. The water from the supply pipe falls into the upper chamber of the aerator and thence down into the stand pipe. As it goes down, an automatic adjustment compels the water to carry with it a predetermined portion of air, the stand pipe being of somewhat greater capacity than it would be for the water alone. The farther down it goes in the pipe the greater becomes the pressure, until, at the connection with the reservoir pipe, the pressure is several atmospheres and oxygen is almost completely absorbed.

"The water is then led to a filter, still under pressure, and the mingled air and water are more minutely subdivided and more oxygen is absorbed. The water is charged now with all the oxygen it will take up, while at the same time the impurities that have been changed into tangible form are filtered out. When the water thus aerated is drawn from the filter, it gives abundant evidence of the quantity of oxygen it has absorbed. The moment the pressure is released the excess of air escapes and the water bubbles as if freshly drawn from a mineral-water fountain. It is so filled with these microscopic bubbles of oxygen that it looks at first like diluted milk, but in a very short time they escape at the surface, and the water sparkles clear and bright, pure as nature supplies from the hills. Where the natural water supply is at such an elevation that no pumping is necessary, the supply pipe may lead directly to the top of the aerator, and thence, with the same action, to the filter and distributing mains. In another application of this principle, the aerator is wholly underground. In this the water is mingled with the air at the top of a deep well. Both are carried down together through a pipe and rise in another, the latter pipe being smaller than, and inside of, the former. The water is thus aerated under great pressure, previous to its passage into the suction of the pump, and so complete is the absorption of air that there is no 'pounding' whatever, as would inevitably result if air were introduced at the pumps, or if it were not perfectly intermingled and absorbed. In all the aerating processes of this system the water carries with it and absorbs 25 per cent. or more of its own bulk of air while under pressure.

"The Hyatt System," by the Hyatt Pure Water Company, New York.

"These systems of aeration, it may be well to state, perhaps, are intended to be applied to the purification of large supplies of water. They seem to be very successful. The question now is, Can the process of water aeration be applied on a reduced scale sufficient to meet the requirements of the carbonating industry ? Carbonated waters especially require water as clear as possible, or else the sparkle, which is one of their essential features, will be lost. The writer believes that after a careful examination of many so-called filters, which at best are merely strainers, the purification of water will he successfully accomplished only by a combination of the aerating process and a filter constructed in accordance with the latest scientific discoveries".