The variety of articles used by the engineer and builder - which are made from burnt or baked clay - is endless.

A few of the more important may now be mentioned.

Perforated Air Bricks are made in stoneware and terra cotta. They are pierced with different patterns, and are most useful for ventilating courses, supplying air to stores, etc.

They are better for this purpose than iron gratings, as they are cheaper, more durable, do not stain the walls with rust, or require painting.

The pattern shown is from Mr. Jennings' circular. They are made in all sizes, from 9x3 inches up to 18 x 18 inches.

Miscellaneous Clay Wares 30051

Fig. 56.

Miscellaneous Clay Wares 30052

Fig. 57.

Damp-proof Courses are made in stoneware (or sometimes in fireclay) pierced with perforations of different patterns.

Miscellaneous Clay Wares 30053

Fig. 58.

Miscellaneous Clay Wares 30054

Fig. 59.

The slabs are generally 9 inches long. They vary from 9 inches to 18 inches in width, to suit different thicknesses of brick wall, and their own height or thickness varies from 11/2 to 23/4 inches.

A damp-proof course slab in stoneware, as made by Messrs. Doulton, with ribbed surfaces and tongue and groove joints, is shown in Fig. 58. A thicker slab, as made by Mr. Jennings, is shown in Fig. 59. The method in which these damp-proof courses are used is explained at page 216, Part II.