General Principles. 37 



repulsion, since it counteracts that of attraction, 

 and seems to keep the particles even of solid 

 bodies from adhering too closely; for an in- 

 crease in the quantity of caloric, we see, ex- 

 pands even the most solid substances, such as 

 metals. Yet we do not consider it as in a state of 

 combination even when present in solid bodies, 

 and still less so when obvious to our senses as 

 producing fire and heat. But it may fairly be 

 considered as in a state of combination when 

 its presence preserves a body in a fluid state, 

 even in the temperature of our atmosphere, as 

 is the case with, water, quicksilver, &C. 



A certain portion (or, in the chemical lan- 

 guage, dose) of caloric reduces a body to the state 

 of an incompressible fluid; a further dose brings 

 it to the state of an aeriform or gaseous fluid. 

 Thus a certain portion of caloric reduces ice to 

 the state of water, a larger dose makes it volatile 

 in the state of vapour. 



Some bodies have a superior attraction for 

 caloric in one state and some in another. Thus 

 mercury will not part with its caloric and be- 

 come solid till the temperature is reduced to 4-0* 

 below 0. Water will not part with it and be- 

 come ice till the surrounding bodies are at 30. 

 But though water retains it obstinately in this 

 state, and though it becomes vapour at 212; yet 

 it readily in this state parts with its caloric to any 

 body colder than itself, and becomes water again. 

 The gasses (or permanently elastic fluids) have 



