82 



found the température-coefficient 6.2 for the reaction 

 between etliylene and bromine ad — 78° C. T r a u t z and 

 Vol km an, ') for the saponification of etliyl-acetate by 

 baryta, give tlie following values for the température- 

 coefficient : 



10° 20« 800 400 



-f = 1.96, — — 2.04, ^^^ = 1.90, ^, = 1.75, 



Qû ' iQo ' 20" 30'^ 



50O 60O 



—- — 1.60, — - = 1.45. 



40O ' 500 



For the saponification ofpropyl-acetate the corresponding 

 values: 1.63, 2.00, 1.81,» 1.70, ].55, 1.43. 



Cohen'') also points out that the température-coefficient 

 in a Chemical reaction is in gênerai liable to vary with 

 change of température. At high températures the tem- 

 pérature-coefficient decreases, at low ones it rises. 



The other reason why van Iterson believes Black- 

 man's theory to be untenable, is that the curve whicli 

 représente the connection between alcoholic fermentation 

 and température, is also a pronounced optimum-curve for 

 a preliminary warming-time of minutes. In my opinion 

 the authors hâve attached too great weight to this 

 objection also. Varions points can be brought forward to 

 explain this phenomenon. 



In the first place, there is the fact already mentioned, 

 that the temperature-coef&cient decreases with a rise of 

 température. 



Further it must be pointed out that van 't Hoff's law 

 applies less strictly in the field of botany than in that 

 of chemistry, for the living organism may not be regarded 

 simply as a homogeneous System, and it is only to such 



1) M. Trautz and K. Tli. Volkman, 1908, p. 68 and 78. 



2) E. C o h e n, 1907, p. 39. 



