122 VETERINARY HYGIENE 



form of facing brick is a machine-pressed clay brick made from 

 carefully prepared pug. These bricks present a more impervious 

 skin to the weather, and are usually of a pleasing and uniform colour. 



Tcrra-Cotta Bricks. Terra-cotta bricks are made from any 

 good clay or mixture of clays which will vitrify at a moderate 

 temperature. They may be obtained in all tints, varying from a buff 

 to a deep red. The colour of terra-cotta work depends upon the 

 proportion of oxide of iron which it contains, the deeper reds result- 

 ing from as much as 10 per cent, of oxide of iron. These bricks 

 are rather expensive, but result in a most durable and weather- 

 resisting surface, have fine arrises, and can be built with close joints. 

 They are used for facing domestic and commercial buildings, and 

 form a good sanitary dado for walls in byres, stables, stable-yards 

 and washing-courts. Terra-cotta work lends itself well to moulding 

 into any shape or decorative form. 



Enamelled Bricks. Enamelled bricks refer strictly to those 

 finished on one or more surfaces with coloured or white enamel, 

 but the term is often loosely applied to cover enamelled, glazed and 

 salt-glazed bricks, which are three totally different products. 



Enamelled fireclay goods of any description, whether bricks, 

 tiles or sanitary fittings, are easily distinguished by reason of their 

 opaque enamel, which does not depend in any way upon the body 

 of the brick for its colour. Before firing, the surfaces to be treated 

 are dipped in the enamel solution, passed into the kiln, and fired. 



Glazed Bricks. Glazed bricks are really glass faced, but they 

 must have a face of china clay, as the glazing, being transparent, 

 would show all the inequalities of an ordinary clay brick and present 

 a rough surface. The china clay facing enables the brickmaker to 

 start with a fine, smooth face. The glazing may be clear or 

 coloured. Glazed bricks are easily damaged on the surface if struck 

 with a sharp pointed instrument, and such fractures are liable to 

 lead to an extension of the damage by crazing, cracking and the 

 absorption of moisture and dirt. 



Salt-Glazed. Salt-glazed bricks are ordinary, good fireclay 

 bricks which have common salt thrown upon the surface while in the 

 kiln. This causes the brick face to flux, and results in a light or 

 dark brown glaze. These bricks are the cheapest form of im- 

 pervious facing brick, and should be used on the lower parts of the 

 walls of all animal habitations. They present a sanitary surface 

 which may be washed with ease. 



Blue Bricks. Most blue bricks are made in Staffordshire from 

 clay which contains from 7 to 10 per cent, of oxide of iron, and 

 are burned in the kiln at a high temperature. They are the hardest 



