^ Method of tncjrtajing the Heat of FiteS. 3 15 



In ufing'thefe balls, care muft be taken to prevent their accumulating at the bottom of 

 the grate : as the coals go on to confume, the balls mixed with them will naturally fettle 

 down towards the bottom of the grate, and the tongs muft bciifed occafionally to lift thcra 

 up ; and, as the fire grows low, it will be proper to remove a part of them, and not to 

 replace them in the grate till more coals arc introduced : a little experience will fliew how 

 a fire made in this manner can be managed to the greatcft advantage, and with the leaft 

 trouble. 



Balls made of pieces of any kind of well burnt hard brick, though not equally durable 

 with fire-brick, will anfwer very well, provided they be made perfeftly round ; but if they 

 are not quite globular their flat fides will get together, and by obftruding the free pafTage 

 of the air amongft them, and amongft the coals, will prevent the fire from burning clear 

 and bright. 



The befl compofitlon fcft* making thefe balls, when they are formed in moulds, and af- 

 terwards dried and burnt in a kiln, is pounded crucibles mixed up with moiflened Stur- 

 bridge clay; but good balls maybe made with any very hard burnt common bricks, reduced 

 to a coarfe powder, and mixed with Sturbridgc 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, which is peculiar to them, and which might perhaps 

 recommend the ufe of them to the curious, even in fire-places conftruded on the bed 

 principles ; they caufe the cinders to be confumed almofl intirely ; 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 dilTicult to account for this effe£l in a 

 fatisfaclory manner, and in accounting for it we fliall explain a circumftancc on which it 

 is probable that the great increafc of the heat of an open fire, where thefe balls are ufed, 

 may, in fome mcafure, depend. The fmall 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 on fome of them ; and, as they are intenfely 

 hot, thefe fmall bodies which alight upon them in their fall, are foon heated red hot, and 

 difpofed to take fire and burn ; and, as frefh air from below the grate is continually making 

 its way upwards amongft the balls, every circumftance is highly favourable to the rapid and 

 complete combuftion of thefe fmall inflammable bodies. But if thefe fmall pieces of coal 

 and cinder fhould, in their fall, happen to alight upon the metallic bars which form the 

 bottom of the grate ; as thefe bars are condudors of heat, and, on account of that circum- 

 ftancc, as well as of their fituation, behnu the fire, never can be made very hot, any fmall 

 particle of fuel that happens to come into contaft with them, not only cannot trfkc fire, 

 but would ceafe to burn, fliould it arrive in a ftate of a£lual combuftion. 



Thefe fa£ts are very important, and well deferving of the attention of thofe who may 

 derive advantage from the improvement of fire places, and the economy of fuel. 



Ss2- There 



