KEEPING WELL 403
and frequently changed, will catch the coarser materials as the water flows through it as effectively as the expensive forms of apparatus, most of which can do little more than this. If one is about to buy a filtering apparatus it is better to first talk the matter over with an intelligent physician or expert chemist, rather than trust to the plausible arguments of the man who has filtering apparatus to sell. In many cities filtering beds are used on a large scale, and sometimes with satisfaction.
As an example of the above, the city of Poughkeepsie, N. Y., which is on the Hudson River, has derived its water supply from that river for many years. The tide water is of course salt, but with the outgoing tide the supply from above the city is fresh. This is pumped into beds of sand which are near the river, and then forced into a reservoir at an elevation of several hundred feet, from which, with ample force, it is distributed over the city.
The addition of certain chemicals to water which is of doubtful purity will destroy animal or vegetable germs which it may contain, and render it innocuous. One of the least objectionable substances which may be used for this purpose is dilute hydrochloric acid. A teaspoonful of this in a quart of water will slightly acidulate it and not render it unpalatable. It is better to use this than to use the stronger, more corrosive acids, which are very dangerous in the hands of the careless or ignorant.
More effective than the use of weak acids, and positively without danger, is the subjection of suspected water to a boiling temperature for half an hour. This will positively destrov all noxious germs. There are many germs which will resist a freezing temperature with ease and apparent comfort, but none have yet been found which would endure boiling. If any sediment remains after the water has been boiled, straining or filtering through a linen towel will remove it. When such water has been cooled it is by no means unpalatable and is absolutely safe. The dead taste which is the more apparent when it is not cold, may be overcome by forcing air into it with a bellows, or by hanging the vessel containing it in a draught, where it will swing back and forth and absorb air, its tempera-