82 Prof. Louis Henry on the Polymerization 



mula indicates the three facts fundamental to the being of the 

 molecule, viz. (1) the nature of its constituent elements, (2) 

 the actual number of atoms of each present, and (3) their 

 combining proportion. 



We are still far from this degree of completeness. Our 

 knowledge of bodies from the molecular point of view is very 

 incomplete, and especially so as regards Mineral Chemistry. 

 Not only is the number of compounds, of which the constitu- 

 tion and structure have been successfully determined, very 

 limited, but there are a great number, I might even say the 

 greater number, to which we are still unable to attribute a 

 formula expressing in a satisfactory manner the true size and 

 real weight of the molecule. The formulae used in Mineral 

 Chemistry are in the majority of cases only the empirical for- 

 mulae, indicating merely the nature and relative weights of 

 the atoms of the elements in the compound, and are wholly 

 silent as to the absolute quantity of matter, or the actual 

 number of atoms present in the molecule. They do not give 

 therefore any idea either of its size, or of its absolute w r eight, 

 or of its internal structure. The properties of compounds do 

 not depend on chance ; they depend chiefly no doubt on the 

 nature of the elements constituting the molecule, but they are 

 also conditioned by the internal structure of the latter, and by 

 its size and weight. 



It is to Berzelius that we owe the idea of isomerism, without 

 which a rational study of the innumerable compounds of 

 carbon would be absolutely unattainable. However it may 

 be, each of these three great factors in the diversity of com- 

 pound bodies exercises a special and preponderating influence 

 on certain classes of properties. If, on the one hand, the 

 chemical activity of a given compound depends especially on 

 the essential nature of the atoms constituting the molecule, 

 and on the constitution of the latter, on the other, an increase 

 in its weight powerfully affects the physical and mechanical 

 properties. 



Whatever may be the specialization of this dependence, the 

 properties of a body, considered individually or relatively, the 

 one in relation to the other, their analogies and their differ- 

 ences, can only be well understood when we know the size of 

 the molecule. 



Just as the adoption of rational and true formulae for the 

 various compounds may render great service in a systematic 

 study, so in the same degree will the adoption of imperfect 

 formulae, artificial and false, or even incomplete and expressing 

 only simple relations, lead to results which are untrue. Such 

 formulae mislead by obscuring, or even by totally concealing, 



