100 



FfFcctof in- 

 creased or di- 

 minUhed 

 temperature. 



Degreei of 

 consistency. 



Constitution 

 ot uieials. 



Zinc. 



Hot short ar.fl 

 cold stiortiron 



Tempering'of 

 sieel. 



ON THE EFFECTS OF HEAT. 



the thermometer therefore will rise. This also agrees with 

 experiment. I have observed it several times this mornino-. 

 The expjinsioii and contraction of gasses, by an increase 

 or diminution of temperature, will be easily explained. 

 As the addition of caloric will increase the density of the 

 atmospheres, expansion must ensue. The abstraction of 

 caloric will occasion a diminution of their density ; the at- 

 traction of the particles, therefore, for each other will pre- 

 vail : they will then approach ; and, in many cases, con- 

 dense into a liquid, or even a solid substance. 



There are many substances, as wax, tallow, &c., which 

 assume various degrees of consistence in passing from the 

 solid to the fluid state. This may be accounted for by the 

 increasing sphericity of the atmospheres, which surround the 

 particles, of which these bodies are composed : as this in- 

 creases, their motion must be facilitated. 



The malleability, tenacity, and ductility of metals, are 

 explained in a similar manner: the atmospheres not being 

 too dense to admit of motion, when a considerable force 

 is applied : and the attraction between the particles beino- 

 sufficiently strong to prevent their separation. When the 

 atmospheres are too dense to permit the motion of particles 

 by the application of a considerable force, the body must 

 be brittle, or exceedingly hard, according as the affinity of 

 the particles for each other varies. When the atmospheres 

 are very far extended, the body will also be brittle, or ra- 

 ther friable, from the diminished attraction of the particles. 

 When zinc is cold, it is brittle, because its atmospheres are 

 too dense to admit of the motion of its particles; a small 

 addition of caloric renders it malleable, by increasino- their 

 sphericity: and a still greater addition renders it friable, by 

 separating the particles too far from one another. Perhaps 

 the difference between hot short and cold short iron may 

 depend, in some degvee, upon a similar cause. When ig- 

 nited steel is suddenly plunged into cold water, it becomes 

 brittle, owing to the separation of too large a quantity of 

 caloric; but by exposure to heat, it may be made of different 

 degrees of hardness, so as to answer various mechanical 

 purposes. We may thus, I think, account for the effects 

 produced by caloric in the tempering of steel : always re- 



collertirg. 



