be named. In preparing articles of food by boiling them in water, we find that they do not get so well done in hard water as in soft; indeed, it is a good plan to boil the water first before using it for such purposes. Greens, boiled in hard water, acquire a dull gray color, as the earthy matters of the water are deposited upon them. If they are cooked in boiling water, which has also been boiled some minutes before, and especially if a small pinch of carbonate of soda and a little salt be added, this defect will be remedied. For making tea with hard water, it is allowable to use a little carbonate of soda, but a great deal too much is commonly employed. For cleansing the skin, hard water is not nearly so efficient as soft."

Thus we claim that all water extensively used should be tested both as to its total, its removable and its unremovable hardness. Where any other inorganic or mineral ingredients of water are suspected to be present in undue proportions, they may be detected by further analysis. In the cretaceous formations of the State, iron pyrites or copperas (sulphate of iron) are common, and the water often has a slightly astringent taste and blackens tea. Soms of the waters are blackened by peat or by the cedar beds of some swamps. It has been claimed that the slight amount of iron and of cedar and pine present in some waters of the State exercise antiseptic powers and so prevent disease.

It is encouraging that there is in every part of the State so much attention now given to inquiry as to sources of water-supply. Yet it is evident that each family needs for itself to have a certain amount of knowledge as to possible sources of pollution. In the case of cisterns, springs, shallow or deep wells, we need to know that they are so made and used as not to expose them to contamination such as is generally an extra demand on the vital forces and too often causes actual disease and premature death.

ON FILTRATION.

PROF. GEORGE H. COOK.

By filtration, I understand the clarification and purifying of water for culinary and household use. The rapid increase in population, and the great number of manufacturing establishments, all over our Eastern States, is every year rendering the stores of water in the ground, and the streams which flow from the surface, and even the rain which falls from the clouds, more impure. Our well-waters, our lake and river-waters, and even our cistern-waters, are liable to be contaminated with impurities-some disagreeable, others dangerous, and all undesirable-and yet from one or other of these we must get our supplies.

How shall we accomplish this end, and at the same time get our supplies pure and wholesome? The answer, in general, must be, by filtration.

The term filtration is by some understood to mean only the straining out from a fluid such particles of floating solid matter as renders it roily or otherwise objectionable in appearance, while others understand by it the removal, not only of the solid floating particles, but also the substances which may be dissolved in it. The first can certainly be done, and the other only to a limited extent.

Water, to be wholesome and acceptable, should be clear and colorless; it should also be free from any organic matter, especially that which is of animal origin, but it is not necessary that it should be entirely free from mineral matter, such as the salts of lime and magnesia, which give the hardness to water. Hard water, even up to that containing fifty or sixty grains to the gallon, is not unwholesome for drinking, though it is very unfit for washing or for making steam. Water which is made hard by the presence of carbonate of lime, may be made soft by the addition of a proper quantity of quick-lime; but sulphate of lime, which causes the hardness in most of the waters of this country, cannot be economically filtered out or separated.

The natural filter of earth, through which the rain and surfacewaters have passed to get into our springs or wells, is composed of the earth and sand which everywhere covers the surface. The water, as it descends through these surface materials, loses the impurities which have given color or opacity to it, and at the same time it dissolves and carries along with it more or less of the minerals it has passed through. Such is the water of our springs and wells when the country is new or thinly sttled. But, as more water is drawn from the wells, and the rain-water has to soak through, the surface impurities, which accumulate with increasing population, are carrried farther and farther downwards till finally the earth and sand will intercept no more of them, and the water passes in its impure, though possibly clear and sparkling state, to the wells, to become the cause of sickness with all its attendant evils. The surface-waters which formerly ran from mountains and forest lands, now run off from cultivated and enriched fields or from the roads and streets of towns and villages, and are still farther contaminated by the waters, impurities and filth which necessarily attend manufacturing processes. All these help to make the water in our streams more impure every year.

Many people still consider the well-water to be the best because it is clear and has the most taste, but the majority of people, especially in our cities and towns, take water from public supplies, which are mostly drawn from streams. Such water is liked because it can be drawn in almost unlimited quantities, directly where it is needed, without pumping or carrying. And, though not so pleasing in appearance, it is probably safer than the well-water. But both of them are dangerous, and something should be done to remove or diminish the danger.

In the case of water from streams, very little has been done in this country to improve its quality beyond what can be accomplished by having large reservoirs and allowing the water to stand in them some time, so that the matters suspended may settle to the bottom, and then to have a wire screen for the water to pass through, while fish or other objects, swimming or floating in the water, are kept back. The organic matters in the water are not removed. Such waters, when left to stand in reservoirs, undergo singular and disagreeable changes, especially during the warmer seasons of the year. Sometimes they have a musty taste and odor, some generate a fishy smell, while others are said to have a cucumber smell. It is not yet explained by what change these effects are produced. Fortunately, though disagreeable, they are not

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generally dangerous. In some of them, as I have noticed, even boiling the water does not remove the peculiar smell. In a case of stored water which came under observation, where a most disagreeable and musty odor and taste was so strongly developed as to be extremely disagreeable, an attempt was made to correct it. The water, on close inspection, was seen to be just a little brownish in color and not perfectly clear. It obviously contained some organic matter. The reservoir of water was about eight feet deep and contained near 4,000,000 gallons. Two barrels or about 500 pounds of alum were dissolved in water and sprinkled over the surface of the water in the reservoir. In the course of two or three days a light scum of slimy coagulated matter gathered on the surface of the water, and was drifted by the wind to the bank. The water itself became perfectly clear and colorless, and its disagreeable smell and taste had disappeared, and this improvement in quality continued several weeks. A like trial has been made on two or three other occasions when the water had developed this disagreeable taste, and the effect was the same in every case. The alum was not sufficient to affect the taste, and I do not think that any one using the water ever suspected there was anything unusual in it. And when the very small percentage used is taken into account, I doubt whether it is possible to detect it by any easy test. Five hundred pounds of alum to 4,000,000 gallons of water, allows 1 pound for 8,000 gallons, or 2 ounces for 1,000 gallons, or about of an ounce for a hogshead of water, and if expressed in the ordinary form of chemical analysis, it would contain only .0016 per cent. of alum.

The trials with this substance are not sufficient to warrant the recommendation of its use, although it is probable that most of the alum is removed in the scum. Still, there may be some well-grounded objections to purifying water in this way. Some more satisfactory and regular mode of purifying water is still needed.

What are called natural filters have been taken advantage of in some cases with success. "Bordering upon all rivers there are found at intervals narrow plains of gravel or sand, brought down and deposited there by the river under the varying positions of its channelway. When these beds of gravel extend to a depth below the bottom of the neighboring stream, they will always be found saturated with water mainly derived from that stream, and however turbid the water of the river, this underground flow will always be found clear, pro

vided that we tap it at a reasonable distance from the channel-way." (Kirkwood on Filtration, page 17.) The water-supply of Newark was attempted by means of a natural filter of this kind. The pumping works are located on a strip of alluvial ground on the west bank of Passaic river, about a mile above Belleville. The surface is but little above high-water mark, and the basins are about 200 feet back from the border of the stream. Two basins were dug in this alluvial plain as deep as the water would easily permit, and they are each 350 feet long and 150 feet wide, walled up with vertical stone walls, and so deep that water will fill them to the depth of 8 feet. The filtration in this way was satisfactory, and the quality of the water was good. The supply needed for the city is from six to eight million gallons daily. At the present depth these basins will not yield that amount, and they have been obliged to open a passage-way from the river and allow the water to flow in without filtration.

It is to be regretted that a more thorough trial of this natural filter has not been made. The sand and gravel is 40 feet or more in depth, and if the basins had been sunk deeper, the filtration into them would have undoubtedly been much more rapid. The pumps are so set that they will not now draw water from much lower than the bottoms of the basins at their present depth, and to get a fair trial of any increased flow would require some new and differently-arranged pumps. In other cases, instead of open basins, long covered underground galleries have been constructed of dry masonry as far in the ground as possible below the surface level of the river, and the water allowed to filter through the sand and gravel of the alluvial plain into these, from whence it can be pumped up for use. The works at Lyons, Genoa, Toulouse, Angers and Pesth, in Europe, are of this sort, and are said to have been eminently successful in providing a good quality of water. The same plan has also been adopted at several places in the United States. At Lowell, Mass., there is a filtering gallery on the north shore of the Merrimac river, parallel with it and about 100 feet from its edge. Its length is 1,300 feet, width 8 feet and height 8 feet. At Columbus, Ohio, there is a long filtering gallery on the border of the Scioto river. It is a brick conduit, 36 by 42 inches, bricks laid close over the upper half and open in the lower. It is 5,715 feet long, and is said to be one of the best examples of this mode of supplying filtered water. The same plan of construction has been followed in the works at Taunton, Mass.