tains a large amount of organic matter, when some preliminary treatment is necessary. Mud should be removed, as bleaching powder will not clarify water. When the bleaching powder is added in properquantities, no unpleasant taste is perceptible in the water nor is any undesirable chemical compound formed in it. Large cities should place their main dependence upon sand filters, but the hypochlorite method may be resorted to as a temporary measure in case a supply pipe breaks or if for any other reason the filtering plant is put out of action. A few years ago, at Germantown, Pa., one of the main supply pipes leading from the filter broke, and it was necessary to furnish part of the town with raw water from the Schuykill River for a few days. Over 300 cases of typhoid fever occurred within a short time in the part of the city using this water. A year or so later a similar accident occurred and it again became necessary to furnish a portion of the city with raw water, but on this occasion the water was treated with bleaching powder, with the result that there was no increase in the number of typhoid fever cases over the number normally present.

Where it is necessary to purify only a small quantity of water the solution is prepared by dissolving 1 teaspoonful of fresh bleaching powder in 1 quart of water. This should be placed in a tightly stoppered bottle and kept away from light. To disinfect water add 1 teaspoonful of the disinfectant solution so prepared to each 2 gallons of water, stir the water thoroughly, and allow it to stand for 15 minutes, when it will be ready for use.

Persons living in the country and in small villages have to depend as a rule upon wells, springs, and cisterns for their water supply. Great care should be taken to prevent their pollution.

The shallow well.-The well should be at least 200 yards away from a stable, privy, or hogpen. If these structures are on a slope, the well should be above them, never down hill from them, as the soil becomes polluted with filth, which may seep through the ground into it. The trough for watering stock, if one is required, should be 40 feet away from the pump and an iron pipe should be used to convey the water to it. The well platform should be higher in the center than at the sides so that water falling on its surface will drain off. This platform should be water-tight and have a raised rim and form a tight joint at the foot of the pump. The curb should be made of concrete, brick, or masonry laid in cement mortar. It should rise 1 foot above the surface and extend 2 feet into the ground. It is important to have the casing water-tight so that no water can enter the well except that which comes through the bottom. Terra-cotta sewer pipe is the best material to use for this purpose. The joints should be held together with cement. The earth should be packed tightly' around the casing. Sand should be used for this purpose, if it is available, as it is a good filter.

The old-fashioned well bucket should not be used, as it may act as a vehicle to carry dirt into the well. This bucket is frequently set on the well platform, where it may be soiled by filth brought to the platform on the feet of a chicken or the sole of a shoe. The water becomes polluted with this material when the bucket is dropped back into the well. The bucket chain or rope may also be soiled by unclean hands when the water is being drawn up or the bucket is being emptied.

such a well through cracks in the platform, is washed into
it by surface water through holes under the platform,
seeps into it through the loose casing, and is carried in
by the bucket or the rope soiled by filthy hands. (Vir-
ginia Health Bulletin, vol. 3, No. 6, 1911.)

Deep or artesian wells.-These wells are less liable to pollution, as the water is not drawn from the soil immediately adjacent to the well. The hardpan or rock through which the bore of the well passes prevents the deep water from becoming polluted by the surface water near the well. The places where this deep water falls upon the ground as rain may be a long way from the well and the

ground through which it travels purifies it. This is the case in all instances except where the water has come through crevices in lime

FIG. 16a.-Heavy pollutions of the soil about the well from the privy, stable, and hogpen will in time overcome the natural purifying agencies of the soil and will seep through the ground into the well. (Virginia Health Bulletin, vol. 3, No. 6, 1911.) stone rocks, as water may travel for miles through such spaces without being purified.

Surface water,

FIG. 17.-Diagram showing pollution of wells in limestone soils. heavily polluted, frequently disappears in a crevice in the limestone and may carry filth to wells and springs near at hand or long distances away. Health Bulletin, vol. 1, No. 14, 1909.)

(Virginia

FIG. 18.-Pollution and protection of a spring. The spring on the left receives pollution by washings into it from the slope above and from the soil immediately around it. It may also be polluted by dirty vessels dipped into it. The spring on the right is protected against surface washings by the ditch and by the concrete spring box. It is inclosed and provided with a discharge pipe so that vessels need not be dipped into it. It furnishes water as pure as when it comes from the ground, unmixed with surface water or filth. It should furnish pure water.

is not properly braced. If the pipe moves or rocks, surface water may flow down a channel along its sides and thus mix with the water at the bottom.

Driven wells are good in sandy regions. Care should be taken to see that they are placed at a safe distance, fully 200 yards from the privy or barnyard. The well should be provided with a tight platform and the earth should be banked up around it. Dirty water should not be employed for priming the well, but only water that has been kept in a clean, covered bucket.

FIG 19.-An insanitary privy of primitive type permitting extensive soil pollution. Reproduced from a photograph. (Original.)

L-H-WILDER

FIG. 20.-Covered can. The simplest type of sanitary receptacle privy. Used with a suitable drying powder, or disinfectant solution, it may be kept sanitary and practically odorless. The seat should be provided with cleats on the under surface to hold it in place on the can. (Original.)

Springs should be inclosed in a brick or cement box with an outlet pipe so arranged that the water may run into a bucket placed beneath it. This arrangement prevents contamination of the spring by dipping the bucket or cup into it. The spring should have a ditch running around it on the upper side to carry off the surface water, as this water, if allowed to flow into the spring, may carry filth and dirt with it. No water from a spring should, of course, be used if the spring is situated on a slope below a stable, insanitary privy, or pigpen, as the water may be polluted by filth which seeps through the ground from such places.