81 



perature than it was at lower température; only at the 

 last inentioned ones it reaches the value to be expected 

 according to van 'tHoffs law. 



Van Iterson points aut, that, according to B lac km an, 

 this decrease of the température-coefficient must be ascri- 

 bed to a harmful influence, but that during the warming- 

 times used hère such an influence h ad not been seen and 

 ho adds: „It must therefore be pointed out very empha- 

 tically, that already on account of the course of the 

 optimum-curve below harmful températures the theory of 

 Duclaux and Blackman must be rejected". 



As regards the values found at harmful températures, 

 i. e. above 45° C, van Iterson also arrives at the 

 conclusion that they do not confirm Black m an's theory. 

 The values of the reaction-velocity found after a time 

 zéro show a distinct optimum, no matter in which way 

 they are determined. The time-curves show only a slight 

 falling off during the first few minutes, which is by no 

 means sufficient to give on extrapolation the values 

 according to van 't Hoff's law, 



Summarising van Iterson mentions as his principal 

 results, that the curve corresponding to a preliminary 

 warming-time of minutes is a pronounced optimum- 

 curve; and secondly that considérable déviations from 

 van 't Hoffs law appear long bcfore the harmful tem- 

 pératures are reached; for thèse two reasons he thinks 

 Blackman's theory must be rejected. 



When trying to answer van Iterson's objections we 

 must make clear at the outset, to what extent v a n 't H o f fs 

 law holds good in the field of chemistry. In doing so, 

 we see that there too the same decrease of the tempéra- 

 ture-coefficient is to be observed. Thus Plotnikowi) 



1) J. P 1 t n i k w, 1905, p. 632. 

 Recueil des trav. bot. Nécrl. Vol. IX. 1912, 



