1 88 BIO-CHEMICAL JOURNAL 



The curves (Fig. 4) reproduce these two series up to seven 

 hours. What we notice is that at the higher temperature the velocity 

 is greater until the equilibrium position at this temperature is 

 approached. The question of equilibrium will be discussed in the 

 next section. In estimating the value of the temperature coefficient 

 of the velocity, some uncertainty exists, since it will differ according 

 to what stage of the reaction we take. If we take as criterion the 

 time taken to reduce the concentration of the solution to a given per- 

 centage, say 90 per cent, at 10, this time is about 2-5 times that at 50, 

 if we take 80 per cent, it is about 1-3 times. In either case, how- 

 ever, it is extraordinarily low ; taking the higher value at 10 it takes 

 twenty-five minutes to become 90 per cent., and at 50 it takes 

 ten minutes, a difference of fifteen minutes for 40 ; so that, 

 assuming uniformity of increase for the total interval, the time taken 

 at 40 would be only ^' = 3-6 minutes more than at 50, or ten 

 minutes and I3'6 minutes respectively. This gives a temperature 

 coefficient of the extremely low value of ^- = 1*36. In the table 

 given by Van t' Hoff 1 there are only two values below this, viz., the 

 dissociation of PH 3 and AsH 3 probably depending on the high tempera- 

 tures at which the observations were taken, since, as Van t' Hoff 

 points out, the velocity-ratios for 10 usually diminish as the tempera- 

 ture rises. The value found in the present case indicates that the 

 theory of Nernst* as to the part played by diffusion-processes in 

 heterogeneous reactions applies here ; the corresponding value found 

 by Brunner 3 for the dissolution of benzoic acid in water is, in 

 fact, 1-5. 



A few observations on the effect of alcohol and certain electro- 

 lytes on the velocity of reaction may be shortly referred to. Congo- 

 red is the sodium salt of a substituted aromatic sulphonic acid, and is 

 less soluble in alcohol than in water, so that it seems probable that 

 more dye would be taken up from a solution containing alcohol than 

 from a watery solution of the same concentration. This was found 



1. Vorles. uber Theor. und Physik. Chemie., 2te Aufl. p. 225. 



2. Zeitsch.f. Physik. Chtmie., XLVII, 1904, p. 52. 



3. Zeitsch.f. Physik. CAemit., XLVII, 1904, p. 62. 



