CHEMICAL PROPORTIONS. 285 



have to consider. If alloiropky is evidenced in the 

 mineral world, it is certainly far more strikingly mani- 

 fested in the vegetable and animal kingdoms. 



There are some cases in which bodies appear to com- 

 bine without any limitation, as spirit of wine arid water, 

 sulphuric acid and water; but these must be con- 

 sidered as conditions of mixture rather than of chemical 

 combination. 



The composition of bodies is fixed and invariable, 

 and a compound substance, so long as it retains its 

 characteristic properties, must consist of the same 

 elements united in the same proportions. Thus, sul- 

 phuric acid is invariably composed of 16 parts of sulphur 

 and 24 parts of oxygen. Chalk, whether formed by 

 nature or by the chemist, yields 43' 71 parts of carbonic 

 acid, and 56'29 parts of lime. The rust which forms 

 upon the surface of iron by the action of the atmosphere, 

 is as invariable in its composition as if it had been 

 formed by the most delicate adjustment of weight by 

 the most accurate manipulator, being 28 parts of iron 

 and .12 parts of oxygen. This law is the basis of all 

 chemical inquiry, all analytical investigations depending 

 upon the knowledge it affords us, that we can only pro- 

 duce certain undeviating compounds as the results of 

 our decompositions. We are not in a position to offer 

 any explanation which will account for these constant 

 quantities in combination. The forces of cohesion and 

 elasticity have been advanced in explanation, 011 the 

 strength of the fact that the solubility of a salt in water 

 is regulated by cohesion, and that of a gas by its 

 elasticity. Although it may appear that some cases of 

 chemical combination are due to these powers, as, for 

 instance, when the union of oxalic acid or sulphuric 

 acid with lime produces an insoluble salt, we cannot 

 thus explain the constant proportions in which the 

 metals, sulphur, oxygen, and similar bodies, unite. It 

 is quite certain there is a power or principle, which we 



