The use of hollow conduits made of baked clay in buildings dates as far back as that of bricks; this has been proved by excavations made in Asia Minor.

The Romans frequently used pipes of pottery to distribute water, and pipes of rectangular section to conduct the hot air which heated their baths.

After their time, these products were very little used, and it was not until the 19th century that they acquired real importance with the manufacture of drain pipes, which began in England at the end of the 18th century, and that of round or square hollow pottery, which dates from the beginning of the 19th century. Then came the introduction of glazed stoneware pipes, which are so valuable in the distribution of water. For a long time the pipes were fashioned by hand, by a series of long and difficult operations. The first attempts at machine-manufacture were made in France, about 1858, by Reichenecker, at Ottweiler (Upper Rhine). The use of machinery extended rapidly, and on all sides appeared different types of machine, all based on the principle of the macaroni press.

Omitting drain pipes, which are not directly concerned with architecture, hollow conduits may be divided into -

I. Water distributing pipes.

II. Pipes for chimneys.

I. Water Distributing Pipes

These are made of ordinary clay or stone-clay. The latter are always glazed, and will be considered under the head of composite pottery.

Manufacture

This comprises, as usual, the preparation of the pastes, moulding, drying, and firing. The choice of clay depends upon the quality of the pipes to be manufactured; for ordinary pipes, such as drain pipes, the clays which are used for hollow bricks will be sufficiently good.

But if a better quality is required, a certain quantity of rich clay must be mixed with the poor clays.

Whatever the composition of the mixture may be, it undergoes preparation by rollers and pug-mills, which convert it into a homogeneous paste free from all impurity and ready for moulding.

Moulding

This is done by machines, as in the case of hollow bricks; the clay, which has been suitably prepared, is pressed into a closed space furnished with a die having an annular orifice of the diameter required for the pipe. One or several pipes may be produced at once, according to the magnitude of this diameter. If it is not very great, the pipes are received upon horizontal cutting-tables similar to those used for bricks. Drainage pipes are so treated; but for pipes of large diameter, these cutting-tables must be modified, or, better still, machines expressing vertically may be used.