1823.] Mathematical Principles of Chemical Philosophy. 2">7 



are the result of the operation of the two great powers, attrac- 

 tion and the repulsive force of caloric. In the present state of 

 chemical science, from the want of some important data, we 

 cannot estimate the effect of these forces, nor compare the 

 relative forces of chemical attraction, which is very different to 

 the order of decomposition ; for it is affected and even inverted 

 by the following causes, the results of the operation of the pri- 

 mary forces upon similar particles. 



1. Temperature. — Heat mercury to nearly its boiling point 

 during several days, giving it access of air; it will be converted 

 into a red oxide ; heat this nearly to ignition, the mercury 

 reassumes its metallic state, and oxygen gas is evolved. At the 

 usual temperature of the air, the attraction of the particles of 

 mercury for each other, and the elasticity of the oxygen gas, 

 prevent their union : at a certain temperature, the former force is 

 so far diminished, that they combine : at a temperature 

 approaching to ignition, the mercury becomes elastic, and the 

 elasticity of the oxygen is amazingly increased, and they are 

 again separated : similarly, at the ordinary temperature of the 

 air, sulphuric or muriatic acid will separate the boracic from its 

 combination with alkaline or earthy bases ; the contrary takes 

 place at a red heat, evidently because the sulphuric and muriatic 

 acids, from their tendency to become elastic, are united to the 

 bases by a less force than at a lower temperature. Many other 

 cases might be advanced to prove that the apparent attractions 

 of bodies for each other are changed by variations of tempera- 

 ture, which acts in two ways ; first, when it favours chemical 

 union, it diminishes the cohesive force of one or more sub- 

 stances ; secondly, when it effects decomposition, it is by giving 

 to one element at least a tendency to become elastic. Hence 

 tables of chemical attraction serve for only one temperature. 



2. Elasticity. — This might have been considered solely as a 

 result of the last cause, but it acts in various peculiar ways at 

 the ordinary temperature, and on this account deserves a sepa- 

 rate place. Carbonic acid is elastic at all temperatures, and 

 probably has a greater tendency to a gaseous state than any 

 other. Its power of saturation is very great, and the force with 

 which it adheres to many bases is peculiarly powerful, yet it is 

 separated from its combinations by every other acid, doubtless, 

 in part at least, from its great tendency to the elastic state at all 

 temperatures. And, in general, bodies which are volatile are 

 separated from their compounds more easily than those which 

 are fixed. Hence carbonic acid will not unite with dry lime, but 

 with its hydrate ; aud phosphorous will not shine in pure oxygen 

 gas. 



3. Cohesion promotes combination when the body to be 

 formed has a great cohesive force, and those to be separated are 

 elastic, fluid or soluble, in the menstruum employed. It opposes 

 it when the substance used for decomposition has a cohesive 



New Scries, vol. v. s 



