July 26, 1901.] 



SCIENCE. 



127 



science during the last twenty years. Let 

 me briefly trace how this physical chemistry 

 has grown, and what it is at present. Al- 

 low me in doing this to rely partly on per- 

 sonal observations. 



When, as a student of the Bonn Univer- 

 sitj, I studied chemistry first, about thirty 

 years ago, under the guidance of one of the 

 most famous men, Kekule, chemical science 

 had, according to our master, come to a 

 dead point. 



The existence of atoms, though an indi- 

 rect chemical conclusion, seemed to have 

 been well established, corroborated as it 

 w^as by the conception of molecules — a con- 

 ception which rested merely on physical 

 grounds. The details about the mutual 

 relation in which these atoms stood in the 

 molecule either were already known, or in 

 the case of complicated or new compounds 

 a knowledge of them was but a question of 

 time. Thus H3COH was used to represent 

 the mutual relations of the atoms in the 

 molecule of a simple compound, methyl 

 alcohol ; that is to say, it was known that 

 three atoms of hydrogen are held in some 

 unknown way by the atom of carbon, the 

 fourth hydrogen atom is held by the atom 

 of oxygen, and this in turn again by the 

 carbon atom. Yet all such formulas were 

 merely schemes in the mind, or diagrams 

 on paper, and chemistry was looking out 

 for a kind of Newton who might tell us the 

 laws which hold together these atoms in 

 their constellations, the molecules. 



You know as well as I that up to the 

 present time this ISTewton has never come. 

 Yet, only a few years after Kekule' s dis- 

 appointing prophecy (which, by-the-by, a 

 teacher should never express before his 

 pupils) stereochemistry awoke, and is now 

 a fully developed and well-founded branch 

 of chemistry. By stereochemistry so much 

 at least was attained that, admitting the 

 existence of atoms, we now know to a large 

 extent, not only the mutual relations, but 



also the mutual positions, which these atoms 

 occupy in the molecule. H3COH becomes 



H 



I 

 H— C— O— H. 



I 

 H 



That is, the three atoms of hydrogen and 

 the atom of oxygen were found to be ar- 

 ranged in space around the carbon atom in 

 such a way as to occupy the four corners of 

 a tetrahedron, in the center of which the 

 carbon atom lies. 



But there we stood, and still stand, since 

 more than twenty-five years, still ignorant 

 of the laws to which their relative position 

 is subordinated, though a recent attempt 

 seems to me hopeful. 



Nevertheless, research went on in a way 

 which had very little to do with that archi- 

 tecture constructed by the mind whose 

 building stones are atoms. So, fifteen 

 years after Kekule's discouraging prophecy, 

 a second child of hope awoke, and this was 

 physical chemistry. It did not appear at 

 once— a scientific branch hardly ever does 

 — it developed as a plant unseen in the 

 shadow, till it felt the sun, and then grew 

 up to be a giant tree. 



Some, as Duhem, even say that physical 

 chemistry is a third fundamental science, 

 entitled to be placed between physics 

 and chemistry. Others, like Winkler and 

 Ladenburg, say that, to begin with, we 

 might allow it a prominent place in chem- 

 istry and substitute for the division into 

 the two branches, organic and inorganic, 

 a division into three. It will be of in- 

 terest to add that the University of Got- 

 tingen has recently organized the chemical 

 department on this principle. But, apart 

 from all principle of division, which in the 

 end is always arbitrary, because our whole 

 science, like nature, which it reflects, is 

 only one thing, though rather large, we ask : 

 What has physical chemistry achieved ? 



