That part of. the work which is out of sight is most important; no elaborate fittings can compensate for imperfect plumbing in the wall or under the floor.

8. Sanitation. - (A.) The disposal of sewage is always one of the gravest problems to consider in the development of a community. The cities upon or near the seacoast have the nearest to ideal conditions for disposing of their sewage, as it is simply emptied into the ocean or one of its tributaries, generally by gravitation, and the action of the tides will carry the matter out to sea, where it is scattered by the ocean currents, and in no case is there any danger of the water supply being affected, as salt water is not used for domestic purposes.

Any lake or river, no matter how large, if it continually receives sewage in any quantity, will eventually be contaminated.

It is not the purpose of this book to discuss the efficiency of the many various systems of disposing of the sewage of inland cities, so we will consider merely the aspects of sanitation with which the carpenter has to deal.

(B.) The privy, which is in common use in rural districts, is prohibited by law in modern towns and cities, where the houses are close together and where a sewer is provided. Even where there is plenty of room, care must be used that the privy is not placed where there is the slightest danger of affecting the water supply, or where it will drain into a brook from which cattle have to drink. It should be located always below the water supply if possible. A privy is usually very obnoxious in warm weather, even at some distance from the house, but it may be made inoffensive by scattering, in the vault, dry earth, which will prevent odors from spreading.

Chamber slops should not be thrown into a privy, but instead should be thrown upon the grass, or in any place where the sun can do its work of purifying.

(C.) Where there is no sewerage system and privies are in common use, the dry earth closet is a simple and efficient method of dealing with this problem. The closet should be light, well ventilated, and fly-proof. The equipment may consist of a box of dry earth or road dust, to be used as often as the closet is, or it may be an elaborate arrangement, in which the earth is thrown in above and handled with a slide, as it is needed. A closet of this sort may be built as close to the house as desired, and if properly cared for, will never be objectionable.

If this form of closet is used, there should be provided a place, perfectly dry and large enough to contain a sufficient quantity of dry earth to care for the privy during rainy weather and the winter months. This should be kept full of road dust, which is well suited for this purpose. The receptacle should be a well made, water-tight, movable box with handles, so it may be easily emptied, though an ordinary vault may be used.

(D.) Water-closets are not possible in all localities, not only on account of the absence of a sewerage system, but because the soil is not adaptable to the construction of a cesspool, which is simply a deep hole, loosely walled to keep the earth from caving in, but which will allow the contents to seep away through the soil. This is connected by a drain to the house, and is the means of disposing of sewage and household waste in many places where there is a sandy subsoil and where there is no danger of contaminating the water supply. It is not considered a system suitable for general use, even in isolated places, as a well a long distance away may be affected; nevertheless, it is used in many places where there is a deep sandy soil.

A method of disposing of sewage, known as the subsurface system, is sometimes used in localities where there are good natural drainage facilities. In this system, the sewage or other household waste is conducted to tanks in which the solid matter is precipitated, and the liquid is distributed through a series of drains laid under the surface of the ground, from which it finds its way to some natural watercourse. This is a complex matter to discuss, and we shall not do more than mention it.

Another method known as the "Septic" consists of beds of sand located in some isolated place, lower than the area which is drained, in which the sewage is exposed to the action of the sun and the air. This method is being used with satisfactory results in small inland communities and by institutions.

(E.) Sink drains should carry as far as possible from the house, and should have as much pitch as can be obtained, not less than 1' in a run of 40', for a 4" drain tile, which is as small as should be used. Under the sink there always should be a trap made perfectly tight with solder. If more than a sink enters the drain, the work of connecting should be done by a plumber, for if improperly done, the effects may be very serious.

A drain should have as few bends as possible in it; the bottom should be laid straight, or in straight sections, regardless of the surface of the ground, and low enough to be well below the frost line.

The end of the drain should empty in a sandy place upon a side hill if possible, as high as the nature of the ground will allow, or otherwise the outlet will freeze in winter and possibly destroy several feet of the end of the drain.

In rural districts the drain often empties upon the top of the ground at some distance from the house, and for ordinary conditions in the country there is little to criticize in this, provided there is no danger of affecting the water supply, as the sun is a great purifier. The drain tile should be laid in cement, with perfectly tight joints, and without low places, or rough cement on the inside of the pipes, to catch the matter from the sink.

9. Refrigerators. - (A.) Refrigeration upon a large scale has become the work of the scientist and the engineer, and we shall not discuss the problem, as it includes very little in which the carpenter would be interested, but we will discuss the construction of an ice refrigerator suitable for family use, or for use in a meat market, or wherever one is needed.