Fire-places and Kitchen Utensils. 343 



it are much less liable to be burned to the sides of 

 the vessel, and spoiled, than when the utensil is formed 

 of a metallic substance. 



There is a very great difference in earthen-ware in 

 respect to its power of withstanding the heat without 

 injury, on being suddenly exposed to the action of a 

 fire, some kinds of it being much less liable to crack 

 and fly, when so exposed, than others ; and, in order 

 to take measures with certainty for diminishing this 

 imperfection, we have only to consider the causes from 

 which it proceeds. Now it is quite certain that the 

 cracking of an earthen vessel, on its being put over 

 a fire, is owing to two circumstances, the brittleness 

 of the substance, and the difficulty or slowness with 

 which heat passes through it; for it is evident that 

 neither of these circumstances alone, or acting singly, 

 would be capable of producing the effect. 



As heat expands all solid bodies, if one side of a ves- 

 sel, composed of a brittle substance, be suddenly heated 

 and expanded, it must crack, or rather it must cause 

 the other surface to crack, unless the heat can make 

 its way through the solid substance of the vessel, and 

 heat and expand that other surface so expeditiously 

 as to prevent that accident. Now, as heat passes 

 through a vessel which is thin sooner than through 

 one (composed of the same material) which is thicker, 

 it is evident that the thinner an earthen vessel for 

 cooking is made, the less liable will it be to receive 

 injury on being exposed to sudden heat or cold. 



I mention sudden cold as being dangerous, and it is 

 easy to see why it must be equally so with sudden heat. 

 If a brittle vessel be (by slow degrees) made very hot, 

 if the heat be equally distributed throughout the whole 



