1. By exposing water contained in bottles to the air of the room.

2.

By drawing a current of air through the water by means of an aspirator.

3. By shaking the water with air in a bottle, in a shaking machine driven by an electric motor, the air being renewed from time to time by removing the stopper from the bottle.

4. By exposing the water to air under a pressure of sixty to seventy-five pounds to the square inch in soda-water siphons.

RESULTS OF AERATION OF WATER BY A CURRENT OF AIR DRAWN THROUGH
THE WATER IN A FLASK BY MEANS OF AN ASPIRATOR,* BY AIR UNDER
PRESSURE, AND BY SHAKING THE WATER WITH AIR IN A BOTTLE.
First Experiment with Cochituate Water.

The air used for aspiration was taken from outside the building. The air of laboratories where gas is burned contains enough nitrogen in the form of nitrites to vitiate an experiment of this character. It was found that there was a very small amount of free ammonia taken up by pure water from the air in the cases of prolonged aeration.

RESULTS OF AERATION OF WATER, ETC. Concluded.
Fourth Experiment with Cochituate Water.

EXPERIMENTS WITH COCHITUATE WATER TO WHICH A SMALL AMOUNT OF

* This decrease in nitrates may have been possibly due to the growth of algae in the bottle.

The variations in the amounts of albuminoid ammonia and the nitrates in these experiments are, in general, too small to have any significance, and fall, in most cases, within the limits of accuracy of the processes used. The loss of free ammonia when the water is aerated is an instance of the driving out of one gas by another. Ammonia cannot be completely removed in this way, but when it is present in considerable amount in a water the effect of aeration by a current of air is very marked. When sewage is thus aerated a very considerable amount of free ammonia passes out with the air.

In some cases the changes in the amounts of nitrogen compounds are not easy to explain as the result of any particular treatment. The problem is a complex one. On the one hand we have the tendency of the organic nitrogen to pass into ammonia, and the ammonia to be oxidized to nitrates, and, on the other, the influence of vegetable organisms in directly assimilating the nitrogen of the ammonia and nitrates. Still, the results, as a whole, show plainly that the aeration of water containing nitrogenous matter and ammonia in considerable amount has no tendency to accelerate the oxidation of the nitrogen.

In the foregoing experiments the nitrogen compounds only were investigated. The oxidation of the carbon of the organic matter represented by the albuminoid ammonia would have as a result the formation of more free ammonia; but, as any inference based on the amount of free ammonia might be complicated by its partial removal by aeration, a series of experiments were made to ascertain directly whether any carbon was oxidized by vigorous aeration. In this series only air under pressure was used, and the evidence of the oxidation of carbon was obtained by the "oxygen consumed" from permanganate, which oxidizes only carbon and hydrogen of organic matter, not nitrogen. Should any considerable oxidation of the carbon take place by the oxygen of the air under pressure there would be a considerable reduction of the amount of permanganate used, or of the "oxygen consumed."

EXPERIMENTS ON THE AERATION OF COCHITUATE WATER BY AIR UNDER PRESSURE OF SEVENTY POUNDS TO THE SQUARE INCH.