January 13, 1905.] 



SCIENCE. 



55 



have reached equilibrium in the allotted 

 time. If he had boiled three hours, the 

 lowest permissible concentration of hydro- 

 chloric acid would luidoubtedly have been 

 less than three per cent. Ansehiitz, on the 

 other hand, worked at ordinary tempera- 

 ture and his solutions consequently needed 

 more acid and more time to approximate 

 to equilibrium. All of this is really first 

 principles and it is only one case out of 

 many. If any one will try to classify and 

 explain the results given in Lassar-Cohn 's 

 book, he will find himself provided with 

 enough interesting research to last him the 

 rest of his natural life. 



The second field for research to which I 

 have alluded is that of irreversible reac- 

 tions. In inorganic chemistry there are as 

 yet no well-authenticated cases where a re- 

 jaction starts and then stops short of equi- 

 librium. The results of Pelabon on hy- 

 drogen and selenium and of Helier on hy- 

 drogen and oxygen have been disputed by 

 Bodenstein and must for the present be 

 considered as wrong. In organic chemistry 

 we appear to have many such reactions, 

 typical instances being the formation of 

 nitro-benzene and the decomposition of al- 

 dehyde into methane and carbon monoxide. 

 AATiile it is possible that these and other 

 reactions run to an end in infinite time, we 

 have not infinite time at onr disposal, and 

 it may, therefore, jirove profitable to find 

 out whether and how the apparent end- 

 point varies with varying initial conditions. 

 This work is desirable now and will become 

 necessary if we should ever revise our opin- 

 ions as to the theoretical possibility of an 

 irreversible equilibrium. By definition we 

 can not determine the existence of an ir- 

 reversible equilibrium by approaching the 

 end-point from the two sides. It seems to 

 me probable, however, that we can draw 

 conclusions from the reaction velocity. If 

 we are dealing with a case of a theoretic- 

 ally rever.sible reaction running practically 



to an end, I can see no reason why the con- 

 centration of the decomposition products 

 should have any effect on the reaction ve- 

 locity, so long as we confine ourselves to 

 gaseous systems. If, however, we are deal- 

 ing with a theoretically irreversible reac- 

 tion which does not run to an end, the reac- 

 tion velocity would vary with the concen- 

 tration of the decomposition products. 



It should be noticed that it will not do 

 to reason from the behavior of a system 

 in presence of a catalytic agent to that of a 

 system without a catalytic agent, since the 

 catalytic agent may displace the equilib- 

 rium. Thus ethyl alcohol is decomposed 

 b}^ heated copper into aldehyde and hydro- 

 gen, while heated alumina changes it chiefly 

 into ethylene and water. It was the study 

 of organic solutes in organic solvents which 

 led Raoult to the formulation of his law. 

 It seems probable that a study of organic 

 reactions may lead to an entirely new class 

 of equilibria. If this happens it will throw 

 much light on the preceding problem be- 

 cause it is very difficult to explain some of 

 the peculiarities in regard to yields in or- 

 ganic chemistry so long as we are obliged 

 to postulate reversible reactions only. 



The theorem of Le Chatelier has been 

 applied chiefly to heat and work effects, 

 but this is by no means the extent of its 

 usefulness. Wherever we get a reversible 

 displacement of equilibrium by light, it 

 must be possible to make use of this the- 

 orem. The change of color of the silver 

 photoclilorides is in accordance with the 

 theorem ; but there seems to be no reverse 

 change in the dark. The simplest case 

 with which to begin would appear to be the 

 formation of ozone. There seems to be a 

 contradiction here. Ozone is known to ab- 

 sorb ultra-violet light and yet it is believed 

 to be formed by the action of ultra-violet 

 light. Whether we are dealing with the 

 same sets of rays in the two eases is a point 

 that has not been settled. In fact, we do 



