BURNING PRICKS. 383 



rompacl as to exclude water. But if too great 

 \iolencc of fire be applied, there will he danger 

 that the bricks, efpccially in the low eft and the 

 middle lira turn, be cither entirely melted, or at 

 leaft, run together. 



4 vii. Attempts to improve Ch w f hy the intermix- 

 tine if ttber Sitblliinccs, arc tf no Service. 



Tin; makers of bricks difapprove of mixing 

 poor clays with a large proportion of fand, earth, 

 and lime : for experience has ihcwn that thcfc 

 fubftances are of no ufe whatever in the prepa- 

 ration of bricks. Yet it is often nof fo much the 

 fubdancc, as the method of preparation followed 

 that i^ faulty. The burning is frequently con- 

 dueled in fuch a manner as to reduce the lime 

 to quick-lime, in which ft ate it abforbs moilture 

 from the atmofphcrc, and caufcs the bricks to 

 crack and form chinks for the reception of walcr. 

 But a more entire burning will obviate this in- 

 convenience, by blending the lime thoroughly 

 with the fand and clay, and producing a fort of 

 vitrification. In this cafe, the lime, inftcad of 

 doing harm, is even of advantage, contributing, 

 in no fmall degree, to the fulioii of the clay. 

 When, fhcrcforc, there happens to be marl in 

 the neighbourhood of a brick kiln, it ought to 

 be preferred to any other fort of earth. But 

 rnarl is liable to various impcrfcclibns which 



render 



