RECENT ADVANCES IN SCIENCE 211 



merely by a diminution of the solubility of the oxygen in the 

 solution. The actual mechanism is not at all understood. 

 Such results remind one of heterogeneous catalysis, especially 

 the catalytic effects of colloidal metals which can be poisoned 

 by minute amounts of foreign material. In the present case, 

 however, we are apparently dealing with homogeneous systems 

 in which the degree of dispersion has attained the molecular 

 limit. No suggestion as to a possible mechanism is made by 

 Bigelow. 



Bigelow's work was extended by Young (2), who showed that 

 negative catalytic effects are produced by alkaloids upon the 

 oxidation of sodium sulphite and the oxidation of stannous 

 chloride. 



The sodium sulphite reaction was taken up later by Titoff (3), 

 the reaction being again carried out under thermal conditions. 

 Titoff discovered a number of positive catalysts for the re- 

 action, chiefly inorganic salts. In this connection copper sul- 

 phate occupies a unique position in virtue of its strong positive 

 effect even at extreme dilution, the influence of one gram- 

 molecule of the salt in ten million litres being measurable. 

 Approximate proportionality was found to exist between the 

 increase in speed and the concentration of the copper salt. 

 The catalytic effect is attributed to the copper ion. When 

 mannitol and copper sulphate are present simultaneously, 

 the rate of the reaction depends upon the relative amount of 

 each ; the net effect indicates mutual influence. Titoff also 

 found that stannic and stannous chlorides exert the greatest 

 negative catalytic influence so far observed. Acids exhibit 

 the very interesting property of accelerating the reaction as 

 long as the hydrogen ion content is small, but on further 

 addition of acid the catalytic effect becomes negative and the 

 reaction finally ceases. 



The view put forward by Luther (4) as an explanation of 

 negative catalysis is that it results from a partial destruction 

 of some positive catalyst already present in the system. Titoff 

 shows that this view leads us to expect that the observed 

 velocity of reaction should be inversely proportional to the 

 concentration of the negative catalyst, which is in general in 

 agreement with experiment. Luther's explanation is probably 

 true in certain cases, but by no means in all. 



The above investigations refer to the oxidation of sodium 



