43° 



MECHANICAL. 



BRICK-MAKING, Hints on.— The art 

 of brick-making is a distinct branch of 

 the useful arts, and does not properly 

 belong to that of the builder; but as he is 

 frequently obliged to prepare this 

 material, the following outline of the 

 process may prove of service. 



The best brick-earth is composed of a 

 mixture of pure clay and sand, deprived 

 of pebbles of every kind, but particu- 

 larly of those that contain lime and 

 pyritous, or other metallic substances ; as 

 these, when in large quantities, and in 

 the form of pebbles, act as fluxes, destroy 

 the shape of the brick, and weaken it, by 

 causing cavities and cracks; but when 

 present in small quantities and equally 

 diffused throughout the earth, they assist 

 the vitrification and give it a more uni- 

 form character. 



Good brick-earth is frequently found in 

 a natural state, and requires no other 

 preparation for the purpose of the brick- 

 maker. 



When he is obliged to prepare the 

 earth by mixing the pure clay and sand, 

 direct experiments should be made in all 

 cases to ascertain the proper proportions 

 of the two. If the clay is in excess, the 

 temperature required to semi-vitrify it 

 will cause it to warp, shrink and crack ; 

 and if there is an excess of sand, com- 

 plete vitrification will ensue under similar 

 circumstances. 



The quality of the brick depends as 

 much on the care bestowed on its manu- 

 facture as on the quality of the earth. 



The first stage of the process is to free 

 the earth from pebbles, which is most 

 effectually done by digging it out early 

 in the fall, and exposing it in small heaps 

 to the weather during the winter. In the 

 spring the heaps are carefully riddled if 

 necessary, and the earth is then in a 

 proper state to be kneaded or tempered. 



The quantity of water required in 

 tempering will depend on the quality of 

 the earth ; no more should be used than 

 will be sufficient to make the earth so 

 plastic as to admit of its being easily 

 moulded by the moulder. 



About half a cubic foot of water to one 

 of the earth is, in most cases, a good pro- 



portion. If too much water be used, 

 the brick will not only be very slow in 

 drying, but it will, in most cases, crack, 

 owing to the surface becoming complete- 

 ly dry before the moisture of the interior 

 has had time to escape ; the consequence 

 of which will be that the brick when 

 burnt will be entirely unfit for use, or very 

 weak. 



Great attention is requisite in drying 

 the brick before it is burned. It should 

 be placed for this purpose in a dry ex- 

 posure, and be sheltered from the direct 

 action of the wind and sun, in order that 

 the moisture may be carried off slowly 

 and uniformly from the entire surface. 

 When this precaution is not taken, the 

 brick will generally crack from the un- 

 equal shrinking, arising from one part 

 drying more rapidly than the rest. 



Too large a proportion of sand will 

 render the brick brittle under this process; 

 while too large a proportion of clayey 

 matter will be indicated by the brick 

 shrinking and cracking. 



The burning and cooling should be 

 done with equal care. A very moderate 

 fire should be applied under the arches of 

 the kiln for about 24 hours, to expel any 

 remaining moisture from the raw brick. 

 This is known to be completely effected 

 when the smoke from the kiln is no longer 

 white. The fire is then increased until 

 the bricks of the arches attain a white 

 heat ; it is then allowed to abate in some 

 degree, in order to prevent complete 

 vitrification ; and is alternately raised and 

 lowered in this way until the burning is 

 complete, which may be ascertained by 

 examining the bricks at the top of the 

 kiln. 



The cooling should be slowly effected ; 

 otherwise the bricks will not withstand 

 the effects of the weather. This is done 

 by closing the mouths of the arches and 

 the tops and sides of the kiln, in the most 

 effectual manner with moist clay and 

 burnt brick, and allowing the kiln to 

 remain in this state until the warmth is 

 perfectly subsided. 



A kiln 13 feet long, 10 feet 6 inches 

 wide and 12 feet high, the walls being 

 perpendicular on the inside, and piled 

 full, deducting the arch openings, will con- 

 tain about 25,000 bricks. 



