PHYSICAL AND LITERARY. 235 



fewel at prefent ufed in that operation is 

 charcoal of oak, and other hard woods j a- 

 ny attempt made to do it with pit-coal, fo far 

 as I can learn, has hitherto proved unfuccefs- 

 ful i and indeed from the nature of that fub- 

 ftance, there feems little hopes of ever bring- 

 ing it to anfwer the end, the bituminous or 

 inflamable part of pit-coal having nearly the 

 fame efFed: upon iron, which common ful- 

 phur has. It deftroys, as experience (liews, 

 the malleability of iron and all other metals. 

 Pit-coal has likeways another bad quality, 

 which I have often found to my coft. With 

 a ftrong heat it runs into a glafTy fubftance, 

 which in time, by its flicking fo clofely to- 

 gether, and to the fides of the furnace, quite 

 choaks it up, and, by its tenacity, hinders 

 the metallic parts from finking downwards, 

 as they would do by their natural gravity. 

 What is chiefly wanted in fmelting, is an o- 

 pen fire ; the furnaces are commonly fuffici- 

 ently clogged with the flony and other he- 

 trogeneous bodies united with the ore, which 

 run into glafs without the addition of any 

 fuch foreign matter as has a tendency to vi- 

 trification. The char'd wood, on the con- 

 . rrary, keeps always an open fire, the in- 

 flamable 



