Cast iron is brittle, but when iron of the proper softness is used, and when the castings are of sufficient thickness, its brittleness need not be an objection.

Wrought iron is smoother, denser, more uniform in thickness and tougher than cast iron and can be absolutely tightly jointed by threading, and is more and more used each year for soil and drain pipes. Wrought iron when exposed uncoated to clean fresh water will rust quicker than cast iron under the same circumstances. On this ground many persons have opposed its use for plumbing. But in view of the extreme slowness of the action of rust in both cases, especially when covered with the fatty deposits which coat the inner walls of these pipes, and in view of the ease and cheapness with which the surface may be protected before laying, this argument loses its force. Experience shows it to be in all respects a reliable and most satisfactory material for the larger sizes of soil and drain pipes.

Joints.

Equally important with the question of the material is the manner in which the several parts are put together, inasmuch as upon this depends not only the safety of the work, but also, in a measure, the choice of the material itself. The question of joining or coupling the pipe will therefore next be considered.

Classification or Requirements.

An ideal joint for waste pipes should possess the following ten characteristics, which may be called the ten commandments of pipe jointing:

(1) It should be airtight even under heavy pressure, and even under considerable deflection.

(2) It should be unaffected by the expansion and contraction of the pipes.

(3) It should be capable of resisting severe jars and strains, both compressive and tensile, such as are occasioned by its own weight and by settlement and movement in the building. In other words, it should be flexible.

(4) It should be of such a form and nature as to admit of its being as easily taken apart for repairs or alterations as it is put together, and this without damage to any part.

(5) Its form and construction should be such as to allow it to be made and put together rapidly, to follow easily the irregular contour of the construction, and to be used immediately after fixing in place.

(6) It should require no caulking or hammering, which is liable to fracture the pipe or its lining.

(7) It should be so formed that any imperfection either in the materials used or in the manner of putting them together can be easily detected from without, without expert aid, since only in this way can the owner be protected against accident or fraud.

(8) It should be compact enough and so constructed as to enable it to be put together and used in contracted places and slots.

(9) It should cause no obstruction to the waterway, and leave no space or pocket for the deposit of sediment.

(10) It should be simple, durable, indestructible, economical, and unobjectionable in appearance.

A pipe joint which shall answer the above desiderata would evidently be suitable for water, gas and other fluids under pressure, as well as for drains.

Classification of the Different Kinds of Joints.

Pipe joints may be divided into five general classes:

II. The flange joint.

III. The sleeve joint.

IV. The screw joint.

V. The flexible joint.

These may be subdivided as follows:

(a) The hand-caulked lead joint.

(b) The machine-caulked lead joint.

(c) The rubber ring joint.

(d) The cement packing joint.

II. The flange joint into:

(a) The spigot and socket flange joint.

(b) The spherical flange joint.

(c) The loose ring flange joint.

(d) The wedge and key flange joint.

(e) The plain non-adjustable flange joint.

(f) The plain adjustable flange joint.

III. The sleeve joint into:

(a) The lead packing sleeve joint.

(b) The plain ring sleeve joint.

(c) The divided ring sleeve joint.

(d) The bolted ring sleeve joint.

IV. The screw joint into:

(a) The flanged screw joint.

(b) The inner ring screw joint.

(c) The outer ring screw joint.

(d) The plain screw joint.

V. The flexible joint into:

(a) The rotary play joint.

(b) The longitudinal play joint.

The ordinary flanged joint secured by bolts, as used by engineers for gas, steam and water pipes, is unsuitable for plumbing purposes on account of the restrictions it presents in obtaining the proper directions, and to meet the different branches used in piping a house. At every point slight variations of direction are required to avoid the beams and other members of construction, and to meet the different fixtures at the proper angle.

The steamfitters' flanged joint has not the flexibility which allows a piece of piping to be turned slightly on its axis in this or that direction before fixing, as is necessary. Hence the ordinary bell and spigot joint, caulked with lead, was substituted for the flanged joint in plumbing. It enabled the plumber to cant the pipe in any direction, or to revolve it on its axis to conform with the irregularities of the construction and fit every contour.

But this joint is in every other respect the most barbarous, expensive and unscientific device imaginable, and it is difficult to understand how it can have acquired the popularity it has. Only one of the new conditions imposed by plumbing has been met in this device; the condition of flexibility in arrangement, as already described. But this condition has been met only at the sacrifice of others far more important. The caulked joint is neither tight nor permanent; it cannot be made to resist water or gas under pressure, and it is soon destroyed by alterations of heat and cold in the pipes, such as is often produced by the passage through them of hot water or steam. It is expensive both in time and material. It requires expert labor to adjust, but defies expert labor to take it apart again without more or less destruction of the piping. Even the process of putting together involves a hammering which endangers the integrity of the pipe, and the most experienced and careful workman often cracks it in the process.