PRESENT PROBLEMS OF TNOROANIf CHEMISTRY. 209 



such tliat the surface ener<»T for e(Hial numl)ers of luoleciiles distrib- 

 uted over a surface is equal for equal iutervals of teui]:)erature below 

 the teuii)erature at which surface (nieri>:y is zero — that is, the critical 

 point. This gives a means of (leterniining the molecular Aveights of 

 liquids, and we assume that the molecular weight of a compound is 

 accui'ately the sum of the atomic weights of the constituent elements. 



2. The volume energy of gases is equal at equal temperature from 

 that at which volume energy is zero — i. e., absolute zero. And it fol- 

 lows that those volumes of gases which possess equal volume energy 

 contain equal numbers of molecules — again, a close connection with 

 atomic weights. 



3. The specific heats of elements are approximately inversely pro- 

 portional to their atomic weights, and of compounds to the quotient 

 of their molecular weights divided by the number of atoms in the 

 molecule. Specific heat and entropy are closely related; hence one 

 of the factors of thermal energy is proportional (nearly) to the 

 reciprocal of the atomic weights. 



4. The ion carries in its migration through a solution one or more 

 electrons. Now, the ion is an atom carrying one or more charges — 

 one for each equivalent. Here we have the capacity for electric 

 charge proportional to the equivalent. 



5. The factors of chemical energy are atomic weight and chemical 

 l)otential ; and as the former is identical numerically, or after multi- 

 plication by a simple factor with equivalent, electric potential is 

 proportional to chemical potential. 



We see, therefore, that surface, volume, thermal, electrical, and, 

 no doubt, other forms of energy have as capacity factors magnitudes 

 either identical with or closely related to units of chemical capacity 

 while kinetic and linear energy are not so related, except through 

 the periodic arrangement of the elements. 



It appears, therefore, to be a fundamental problem for the chemist 

 to ascertain, first, accurate atomic weights, and, second, to investi- 

 gate some anomalies which still present difficulties. In America you 

 iiave excellent workers in the former branch. Mallet, Morley, 

 I\ichards, and many others have devoted their time and skill to per- 

 hai)s the best work of this kind which has been done, and F. W. 

 Clarke has collated all results and afl'orded incalculable help to all 

 who work at or are interested in the subject. Valuable criticisms, 

 loo, have been made by Hinrichs; but it must be confessed that, in 

 spite of these, which are perhaps the best determinations which have 

 been made, the problem becomes more and not less formidable. 



There are lines of work, however, Avhich suggest themselves as pos- 

 sibly likely to throw light on the question. First, there is a striking- 

 anomaly in the atouiic weight of nitrogen, determined by analysis 

 SM 1UU4 14 



