IxiV FHOCEEIHNGS. 



valence wliicli any atom exhibits is eight. 'IMie eft'cet of this exten- 

 sion of the atomic theory was to vastly increase its usefulness. It 

 now became possible to formulate relationships between the atoms 

 in the molecules of even complex organic compounds. In other 

 words, chemists were now able to form a mental picture of the 

 internal mechanism of molecules of compounds, which, whether it 

 corresponded closely to fact or not, at least justified itself, for it 

 greatly facilitated chemical investigation. A single example will 

 serve to illustrate this. An analysis of acetic acid shows that it 

 is composed of -40.11 per cent, carbon, 6.80 per cent, hydrogen, 

 and 53.0'.) per cent, oxygen. Expressed in the language of tlie 

 atomic theory, this composition would be given by the formula 

 CH^O. Physical as well as chemical considerations lead to a mole- 

 cular fnimula just dmible this, or (\,H,().,, expressing, of course, 

 the same composition. Now experiment shows that one-quarter 

 and no more than one-quarter of the hydrogen in acetic acid can 

 be replaced by an equivalent weight of a metal, as sodium, yielding 

 sodium acetate. The remaining three-quarters cannot l)e so 

 replaced. This fact is expressed in terms of the atomic theory 

 by the statement that one hydrogen atom in the molecule of acetic 

 acid bears a relation to it different from that of the other three. 

 Again, experiment shows that in a wide variety of reactions where 

 one-quarter of the hydrogen of the acid is abstracted from it, one- 

 half of the oxygen also disappears at the same time, and these 

 quantities of hydrogen and oxygen reappear again together in one 

 of the products of the reaction. The inference is that part of the 

 oxygen and hydrogen in acetic acid are c-loscly associated, or, in 

 terms of the atomic theory, one of the hydrogen atoms in the 

 molecule is closely combined with, or linked to, one of the oxygen 

 atoms; and as the valence of hydrogen is unity ami that of oxygen 

 two, the hydrogen must be attached to the rest of the molecule 

 by means of the oxygen; and hence if the oxygen is split off the 

 hydrogen must go off with it. Proceeding in this way, interpret- 

 ing experimental results by the atomic theory and its extension 

 in the theory of valency, we finally arrive at a mental picture of 

 the molecular structure of a compound. Xr)w the important 

 feature is t1iat tliis mental pictinv may suggest new methods of 



