3*4 PROCESS FOR 



render it Icfs fuitable as a material for brick?. 

 The chief of thefe, its containing too large a pro- 

 portion of lime, may be remedied by the addi- 

 tion of clay. Another fault of marie is, when 

 its parts have too great a tendency to vitrifica- 

 tion ; but the addition of filiceous earth rcclifie* 

 this*. Care muft likewife be taken, that the 

 lime be fufliciently pulverized. If it be in lumps, 

 the .procefs is more likely to milcarry. 



vin. Experiments of tie slutbor. 



I AM now to give an account of a ferics of ex- 

 periments which I made upon common clay, 

 without any admixture of lime, and two dille- 

 rent forts of marl both dug near Upfal. Of 

 ihefc earths I had bricks formed and burnt, fome 

 without any fund, others with one-fourth of fund 

 to three-fourths of clay. Thole in which there 

 was no fand did not crack as they were dried; 

 from which it appeared that the fubftancc of 

 which they were compofed, was of itfclf, without 

 any addition whatever, fufficiently fuitable as * 

 material for bricks. Of the bricks fume were 

 burnt till they became red, and toother* a more 

 intenfc heat was applied, which gave them a dm k 

 brown colour and rendered them hard on the 

 furface. But the hardeil were thofc into the 



compofltion 



* f iv. v. 



