ON THE PHYSICAL VI KW OF NA'iTHE. 



171 



Willard Gihlts ^ in America. They seem to have l^een the 

 first to approach the question of chemical equilihrium, 

 the result of llie action nf various conflicting cliemical 

 forces, termeil ailiiiities, from a general comjirehensive 

 j)oint of view ; recognising that the theory then com- 

 monly adopted on the Continent — the thermo-chemical 

 thenry of atlinity — was incorrect <ir incom])lete. This 

 theory, which had l)een principally ehil)orated by Julius 

 Thomsen in Copenhagen and l)y Berthelot in l-'iance, 

 was supi)orted l>y tlie large amount of valuable ex- 

 perimental research for whicli we are indebted t<^ 

 these two eminent men and their numerous follnwcrs. 



whilst chemists pemsted in the ex- 

 clusive use of atomistic concej)tions, 

 which, as Horstinann pointed out, 

 are of no avail in problems of that 

 nature (see Helm, 'Energetik,' p. 

 143). 



^ More fundamental than the 

 labours of Hor.«tmann were those of 

 Gibbs, which began with the year 

 1874, and were for a long time 

 buried in the ' Transactions of the 

 Connecticut Academy." They were 

 known to Maxwell, but remained 

 generally unknown, partly owing 

 to their abstract nature, partly 

 to the fact that the majority of 

 Continental chemists wore not 

 prepared to appreciate the mathe- 

 matical form in which his exposi- 

 tions were clothed. Previous to 

 the study of questions of chemical 

 equilibrium, Gibbs had successfully 

 developed an idea of .lames Thom- 

 son's — viz., the graphical re])resen- 

 tation of the diti'erent thermo- 

 dynamic ([uantities in three instead 

 of merely in two dimensions. Thom- 

 son had lepresented the projierties 

 of a body or system by referring 

 them to volume, pressui-e, and tem- 

 perature. Gibbs refers them to 



volume, energy, and entropy, tlie 

 former quantities being always de- 

 finable by the latter, but nut vice 

 rcrtsa. The advantages of this rep- 

 resentation were demonstrated to 

 English students in Maxweirs 

 ' Theory of Heat." In Germany it 

 was Prof. Ostwald who, by collect- 

 ing and translating the memoirs 

 of Gibbs, first made them accessible 

 to students (' Thermodynamisciie 

 Studien," von Willard tlibbs. Leipzig, 

 1892). Subsequently both Ostwald 

 and Helm have done much to pro- 

 mote an understanding of Gibbs's 

 methods. See Ostwald, 'Allg. 

 Chemie," vol. ii. part 2, p. 114, 

 &c. ; Helm, ' Grundziige der niathe- 

 matischen Chemie" (Leipzig, 1S94), 

 and 'Energetik,' passim. Subse- 

 quently Gibbs also introduced the 

 very general and useful term 

 "phase" to denote tiie different 

 states in which a substanc-e can 

 exist. This term denotes not only 

 such difl'erences as were formerly 

 called in German Af/i/rrt/atztutUindc, 

 but likewise conditions of dis- 

 sociation, allotropic and isomeric 

 modifications. 



