Expression machines only allow of the manufacture of straight pipes and, by heading the fresh pipe with the hand as it issues from the die, of those having a slight curvature.

When the curvature is too pronounced (Fig. 585), we must have recourse to moulding, and this is done in plaster moulds which are in two parts, and have a central core equal in breadth to the inner diameter of the pipes to be manufactured. As for the single (Figs. 584, 588), double (Fig. 586), or perpendicular (Fig. 587) junction pipes, they are made by hand. We take two pipes which have been expressed by the machine and are sufficiently firm; by means of templates the part where the junction is to be is cut out and removed from each pipe, then the join is made in the usual way by thoroughly welding together the clay of the two pipes.

Drying

Drain pipes are dried in the open air under sheds in which are arranged horizontal wooden shelves; the pipes are laid flat upon these, and are turned over from time to time to assist desiccation.

Socket-tiles are dried in storeyed drying-places, and are simply placed socket downwards on the floor. The volume of these pipes being large (diameters vary from 2 to 20 inches, and even more for certain pipes of limited sale), a large space is required.

Firing

All brick-kilns are available for firing pipes; intermittent covered kilns are used, but preferably continuous kilns. The pipes are placed upright, side by side, small ones being put inside larger ones to economise space, The fire is managed as in the case of bricks, but its action is more rapid on account of the thinness of the products being baked and the frequent vacant spaces.

Fig. 583.

Fig. 584.

Fig. 586.

Fig. 587.

Fig. 588.

Fig. 589.

Fig.590.

Fig.591.

Figs. 583 to 591. Pipes for Water Conduits (Brault) and for Drains (Legros).

II. Chimney Conduits

These are divided into ventiducts or round "boisseaux" (Fig. 592), rectangular "boisseaux" (Fig. 593), and "wagons" (Figs. 594, 595), more especially used in Paris.

They are made like other pipes, with machines expressing vertically. The oblique or canted "wagons" are made by inclining the receiving plate. The socket of the "boisseaux" is cut out of the thickness of the sides, and this is done by hand when the paste is firm enough to keep its shape. At one end paste is taken away from the outside, and at the other from the inside.

To make connection between the " wagons" they are provided with projections which fit together. These projections are made by the machine when they are continuous, like the dovetails on straight (Fig. 600) or oblique (Fig. 601) "wagons"; when they are interrupted (Figs. 598, 599), they are made by hand.

The dimensions of "wagons" and "boisseaux" are extremely variable; the interior dimensions may vary between 5 inches by 6 inches, and 12 inches by 20 inches, with a length of from 13 to 20 inches. (See table).

Fig. 592.

Fig. 593.

Fig. 594.

Fig. 595.

Fig. 596.

Fig. 597.

Fig. 598.

Fig. 599.

Fig. 600.

Fig. 601.

Figs. 592 to 601. Ordinary (Perrusson), Cross-joint (Gilardoni freres), and Dove-tailed (Arthur Metz) "Boisseaux " and " Wagons".

The drying and firing of these products do not present any special difficulty.

Pipes. Applications

"Wagons" are much used for forming chimney conduits inside walls; this is an interesting and a recent application of pottery to the construction of buildings.

When several conduits are placed side by side they must be bound together, and for that purpose the dove-tailed "wagons" (Figs. 590, 600, 601) are to be recommended.

Chimney Tops. (See roofing accessories, p. 335).

Details As To Pottery For Building