CONSTITUTION OF CHEMICAL COMPOUNDS. XXI 



tion of these free affinities upon each other ; and, the com- 

 pounds once formed, the affinities are no \onger free. Upon 

 this mutual neutralization or saturation of free affinities 

 are based our fundamental ideas in regard to the constitu- 

 tion of chemical compounds, or chemical structure. The 

 compounds of the elements with hydrogen alone are very 

 simple. We have hydrochloric acid, for instance, consist- 

 ing of one atom of hydrogen united with one atom of 

 chlorine ; and the molecule of the compound is represented 

 by the formula, H.C1 ; and so also for hydrobromic acid, 



f TT 



H.Br., etc. For water we have H.O.H or O \ jr which sig- 

 nifies that each of the free affinities of the bivalent oxy- 

 gen atom is saturated by a hydrogen atom ; for ammonia 



.H (H 



we have N.H or N < H ; for marsh gas, CH 4 , we have 



H (H 



H. .H 



C or C < j These formulae indicate the constitution 



[H. 



of the compounds, i. e., the arrangement of the atoms in the 

 molecule. By the expression "arrangement of the atoms 

 in the molecule, "however, we do not intend to go so far as 

 to refer to the actual relative position of the atoms in 

 space, as our present knowledge will not permit conclu- 

 sions of any value in regard to this point. We only mean 

 to give an account of the employment of the affinities of 

 the atoms, which are the essential causes of the formation 

 of the molecules. In the case of hydrochloric acid, for 

 instance, we mean that the one free affinity originally pos- 

 sessed by the hydrogen-atom, and that possessed by the 

 chlorine-atom, as inherent, characteristic powers, have 

 been mutually satisfied, and, ceasing to be free affinities, 

 now perform a function in holding together the two atoms, 

 in order to form the molecule of the compound. It may 

 be here mentioned that the so-called free affinities are in 

 almost all cases never free except for an infinitesimally 

 short space of time. An atom of hydrogen or of chlorine 

 does not exist in a free condition, but, if nothing else be 

 present with which it can combine, it combines with 

 another atom of the same kind, forming a molecule of the 

 element instead of a molecule of a compound. The mole- 

 cule of hydrogen, or of chlorine, has the same chemical 



