obtained in the Combujlion of Fuel. 43 



kiln, is pounded crucibles mixed up with moiftened Stur- 

 brldge day ; but good balls may be made with any very hard 

 burnt common bricks, reduced to a coarfe powder, and mixed 

 with SlUrbridge clay, or even with common clay. The balls 

 fhould always be made fo large as not to pafs through between 

 the front bars of a grate. 



Thefe balls have one advantage, whieh is peculiar to them, 

 and which might perhaps recommend the ufe of them to the 

 curious, even in fire-places con(lru6ted on the bed principles ; 

 they caufe the cinders to be confumed almoft entirely; and 

 even the very afhes may be burnt, or made to difappear, if 

 care be taken to throw them repeatedly upon the fire when 

 it burns with an intenfe heat. It is not difficult to account 

 for this effect in a fatisfaclory manner, and in accounting for it 

 we (hall explain a circumitance on which it is probable that th<s 

 great increafe of the heat of an open fire, where thefe balls are 

 ufed, may, in fome meafure, depend. The (mall particles of 

 coal and of cinder which, in a common fire, fall through the 

 bottom of the grate and efcape combuftion, when thefe balls 

 are ufed can hardly fail to fall and lodge op fome of them ; 

 and, as they are intenfely hot, thefe final! bodies which alight 

 upon them in their fall, are foon heated red-hot, and dif- 

 pofed to take lire and burn ; and, as frefli air from below the 

 grate is continually making its way upwards amongft the 

 balls, every circumftanee is highly favourable to the rapid 

 and complete combultion of thefe fmall inflammable bodies. 

 Hut if thefe fmall pieces of coal and cinder ihould, in their 

 fall, happen to alight upon the metallic bars which form the 

 bottom of the grate ; as thefe bars are conductors of heat, 

 and, on account of that circumftance, as well as of their fitu- 

 ution, bthj-w the fire, never can be made very hot, any fmall 

 particle of fuel that happens to come into contact with them, 

 not only cannot take fire, but would ceafe to burn fhould it 

 arrive in a Hate of actual combuftion. 



Thefe facts are very important, and well deferving of the 

 attention of thofe who may derive advantage from the im- 

 provement of fire-places, and the ceconomy of fuel. 



There are fome circumltances which ftronglv indicate that 

 an admixture of incombuftible bodies with fuel, and efpe- 

 eially with coal, caufe an increafe of the heat even when the 

 fuel is burnt in a clofed fire-place. No fire-place can well be 

 contrived more completely clofed than thofe of the iron ftoves 

 in common ufe in the Netherlands ; but in thefe (loves, which 

 are heated by coal fires, a large proportion of wet clav is al- 

 ways coarfely mixed with the coals before they are introduced 

 into the fire-place. If this pradtice had not oeen found to be 



ufeful, 



