CHAPT2R VI. 



FIRE-CLAY AND ANTHRACITE. 



FOR household fireplaces, whether open or closed, these may 

 be regarded as the material and the fuel of the future, and 

 should be more generally and better understood than they are. 



The merits of fire-clay were fully appreciated and described 

 nearly a hundred years ago by that very remarkable man, 

 Benjamin Thompson, Count of Rumford. Any sound scien- 

 tific exposition of the relative value of fire-clay and iron as fire- 

 place materials can be little more or less than a repetition of 

 what he struggled to teach at the beginning of the present 

 century. 



It is impossible to fairly understand this subject unless we 

 start with a firm grasp of first principles. The business before 

 us is to get as much heat as possible from fuel burning in * 

 certain fashion, and to do this with the smallest possible 

 emission of smoke. Substances that are hotter than their 

 surroundings communicate their excess of temperature in three 

 different ways: 1st, by Conduction; 2d, by Convection; 

 3d, by Radiation. All of these are operating in every form 

 of fireplace, but in very different proportions according to 

 certain variations of construction. 



To demonstrate the conduction of heat, hold one end of a 

 pin between the finger and thumb, and the other end in the 

 flame of a candle. The experiment will terminate very speed- 

 ily. Then take a piece of a lucifer match of the same length 

 as the pin, and hold that in the candle. This may become 

 red-hot and flaming without burning the fingers, as the pin did 

 at a much lower temperature. It matters not whether the pin 

 be held upward, downward, or sideways, the heat will travel 

 throughout its substance, and this sort of travelling is called 

 "conduction," and the pin a "conductor' 1 of heat. The 

 conducting power of different substances varies greatly, as the 

 above experiment shows. Metals generally are the best con- 

 ductors, but they differ among themselves ; silver is the best 

 of all, copper the next. Calling (for comparison sake) the 

 conductivity of silver 1000, that of copper is 736, gold 532, 



