Febeuaey 16, 1900.] 



SCIENCE. 



243 



means of it many cases of isomerism have 

 been satisfactorily explained, whose mean- 

 ing was entirely shrouded in darkness be- 

 fore the theory was proposed. By means 

 of this theory large numbers of isomeric sub- 

 stances have been predicted, and many of 

 these have already been discovered. 



The theory of the space relations in car- 

 bon compounds has led directly to a theory 

 of the stereochemistry of compounds con- 

 taining nitrogen, and some extremely inter- 

 esting and important work has been done 

 in the last ten years upon this problem. 

 Under the guidance of these new concep- 

 tions entirely new classes of compounds 

 have been brought to light, and cases of 

 isomerism discovered whose existence could 

 never have been suspected, had not the 

 theory of the tetrahedral carbon atom been 

 proposed. 



If we look over the field of organic chem- 

 istry in a broad way,' it is not too much to 

 say that the most important advances which 

 have been made in organic chemistry in the 

 last quarter of a century, have centered 

 closely around this theory of the tetrahedral 

 carbon atom. If we think only of the appli- 

 cations of the theory which have been made 

 by Wislicenus, Hantzsch, and Emil Fischer, 

 we shall see that it has contributed more to 

 the advancement of our knowledge in this 

 field, than any suggestion since Kekule pro- 

 posed the benzene hypothesis which bears 

 his name. 



In 1878 Van't Hoff published a book 

 which is but little known, and which has had 

 but little direct influence — ' Ansichten iiber 

 die organische Chemie.' But this book is 

 closely connected with his second great con- 

 tribution to chemistry. 



He attempted to develop a side of organic 

 chemistry which had hitherto received but 

 very little attention. What would be the 

 effect of different masses of one substance 

 ■when allowed to act on a given mass 

 of another substance? This quantitative 



side of organic chemistry had been either 

 entirely neglected, or dealt with only as 

 affecting the yield which would result from 

 the reaction. Van't Hoff applied the law 

 of Guldberg and Waage to organic re- 

 actions, and pointed out the importance 

 of the study of the dynamics of reactions. 

 He studied the velocity with which given 

 reactions would take place, and the condi- 

 tions under which equilibria in chemical 

 processes were established. His first results 

 were published in his 'Etudes de Dynamique 

 Chimique ' in 1884. 



The work is not simply experimental. 

 Indeed its theoretical side is of the very 

 highest importance, since it was shown here 

 that we can apply thermodynamics to chem- 

 ical processes. The whole science of chem- 

 ical dynamics and statics has acquired an 

 entirely new meaning in the light of this 

 work, which has contributed more to place 

 organic chemistry on a quantitative basis, 

 than any investigation which has ever been 

 published. This work was greatly enlarged 

 and published in 1896, under the title ' Stu- 

 dien zur chemischen Dynamik,' by Van't 

 Hoff and Cohen. 



The second epoch-making work of Van't 

 Hoff is much less widely known than the 

 first. This is due in part to the compara- 

 tive complexity of the processes dealt with, 

 and in part to the rigorous mathematical 

 treatment which he applied to them. But 

 I belie ve that time will show that the Chemical 

 Dynamics of Van't Hoff is vastly more im- 

 portant than his Stereo-chemistry in placing 

 chemistry upon that exact mathematical 

 basis, toward which all branches of natural 

 science tend, as our knowledge of the phe- 

 nomena becomes deeper and deeper. 



The third great work of Van't Hoff still 

 remains to be considered. I refer to the 

 relation which he showed to exist between 

 the pressure of gases and the osmotic pres- 

 sure of solutions. The genesis of this idea 

 has been furnished us by Van't Hoff him- 



