BURKING BRICKS. 38$ 



compoiltion of 'which a fourth part of fund had 

 entered. Others which had been cxpofcd to the 

 moll intcnfe heat, (Veiled and afllimed the form 

 of a black fibrous Hag. The bricks, after being 

 burnt and cooled, were caft into water, which, 

 after abforbing copioufly, they were removed, 

 and e.xpofed for three whole years, to the open 

 air. Thole which had been cxpofcd for the 

 ihortcfl time to the fire, were almoft totally dc- 

 llroycdand crumbled down by the aftion of the 

 air; fuch as had been more thoroughly burnt, 

 fullered lefs damage; and upon thofe which were 

 formed folely of clay, and had been half vitrified 

 on the furface by the action of a very ftrongfire, 

 not the flighted alteration was produced by the 

 influence of the air and weather* 



5 ix. Advice relative to tie burhing tf Bricks. 



FROM thcfe experiments in the fmall way 

 a judgement may be formed, how far any clay is 

 proper 'as a material for bricks. The more clay is 

 liable to contract ion in drying, the greater ad- 

 dition of fand docs it require. The bed clays 

 are thofe which need no fand. For, with fuch, 

 the labour is abridged, and the bricks are ofafu- 

 pcrior quality. The colour, after burning, fliews 

 whether there be any iron in the bricks. The 

 nature and appearance of the matter varies with 

 the degrees of the heat to Which it is expofcd ; 

 B b and 



