316 SCIENCE IN SHORT CHAPTERS. 



This demands a little more trouble and care in lighting the 

 fire, owing to the absence of bottom-draught, but when 

 the fire is well started the advantages of this further encas- 

 ing in fire-clay are considerable. They depend upon another 

 effect of the superior radiant and absorbent properties of 

 fire-clay that I will now explain. 



So far, I have only described the beneficial effect of its 

 radiation on the room to be heated, but it performs a further 

 duty inside the fireplace itself. Being a bad conductor, it 

 does not readily carry away the heat of the burning coal 

 that rests upon it, and being also an excellent absorber, it 

 soon becomes very hot i.e., superficially hot, or hot where 

 its heat is effective. This action may be seen in a common 

 register stove with fire-clay back and iron sides. "When the 

 fire is brisk the back is visibly red-hot, while the sides are 

 still dull. If, after such a fire has burnt itself out, we care- 

 fully examine the ashes, there will be found more fine dust 

 in contact with the fire-brick than with the iron i.e., evi- 

 dence of more complete combustion there ; and one of the 

 advantages justly claimed by Mr. Fletcher is, that with his 

 solid fire-clay bottom there will be no unburnt cinders 

 nothing left but the incombustible mineral ash of the coal. 

 Economy and abatement of smoke are the necessary con- 

 comitants of such complete combustion. 



A valuable "wrinkle" was communicated by Mr. Flet- 

 cher. The powdered fire-clay that is ordinarily sold is not 

 easily applied on account of its tendency to crumble and 

 peel off the back and sides of the stove after the first heat- 

 ing. In order to overcome this, and obtain a fine compact 

 lining, Mr. Fletcher recommends the mixing of the fire- 

 clay powder with a solution of water-glass (silicate of soda) 

 instead of simple water. It acts by forming a small quan- 

 tity of glassy silicate of alumina, which binds the whole of 

 the clay together by its fusion when heated. 



Londoners, and, in fact, Englishmen generally, have hith- 

 erto regarded anthracite as a museum mineral 'and a curi- 

 psity, rather than an everyday coal-scuttle commodity. If 

 it is to be the fuel of the future, it is very desirable that we 

 should all know something about its merits and demerits, 

 as well as the possibilities of supply. 



