188(i.] NEW YORK ACADEMY OF SCIEJSCES. 180 



Professor Langley ^'' discussed tlie problems of chemical dyiui- 

 mics, and pointed out tlie rich store of promise in this neglected 

 field. Physics deals with three quantities — space, mass, and 

 time. Cliemistry has too long been content with studying the 

 changes of matter in terms of space and mass only, that is to 

 say, in units of atomic weight and atomic volume. The dis- 

 covery of a time-rate for the attractions due to affinity is des- 

 tined to throw new light on chemical science, and to render it 

 cai)able of mathematical treatment. 



(12.) A prodigious amount of work has been done in thermo- 

 chemistry, and within a few years, the multitude of isolated ob- 

 servations have been collected, classified, and made available. 

 The importance of this undertaking will be more appreciated in 

 the future than it has been in the immediate past. 



In all cases of chemical cluinge, energy in the form of heat is 

 either developed or absorbed, and the amount is as definite in a 

 given reaction as are the weights of the substances concerned; 

 hence, measurement of the quantity of heat set free or absorbed 

 in chemical reactions often enables the chemist to determine the 

 true nature of the change. For example, the exact condition of 

 certain bodies in solution can only be conjectured from certain 

 physical characters, few and ill-defined; but by thermic methods 

 of investigation the bodies formed can be accurately ascertained. 

 This is accomplished by reference to the law of maximum work. 

 *' In any reaction, those bodies, the formation of which gives 

 rise to the greatest development of heat, are formed in prefer- 

 ence to others." Thus the thermometer alone in skilful hands 

 determines the a priori necessity or impossibility of a reaction." 



Berthelot," in Paris, and Thomsen,^'- in Coi)enhagen, have 

 })ursued the subject of thermo-chemistry witli indefatigable 

 zeal, and their published results form monuments of exhaustive 

 researcii. ''By the labors chiefly of these two men, we now 

 know the thermal values corresponding to many thousands of 

 chemical reactions. We have learned that the energies of a re- 

 action which can be brought about in two methods, either in the 

 dry way or by solution, differ in the two cases; that salts in so- 

 lution are in a partial state of decomposition; that the attraction 

 of a polybasic acid radical is not the same for the successive por- 

 tions of base added, and that the behavior of a monobasic acid 

 in solution differs essentially from that of a dibasic or tribasic 

 acid. We also know that the total energy involved in any reac- 

 tion is largely influenced by the surrounding conditions of tem- 

 perature, pressure, and volume."*^ 



(13.) The interesting border line between chemistry and 

 physics is an increasing subject of research on the part of both 

 -the chemist and the physicist. The periodic press chronicles 



