Apbil 15, 1904.] 



SCIENCE. 



631 



ides and iodides, whereas fluorides do not in- 

 hibit the catalysis. It is to be observed that 

 silver chloride, bromide and iodide are in- 

 soluble and that silver fluoride is soluble. 

 This fact explains why chlorides, bromides 

 and iodides inhibit the catalysis while fluor- 

 ides do not, as in the latter case no insoluble 

 coating can be formed. Silver cyanide is 

 insoluble and hence hydrocyanic acid and the 

 soluble cyanides inhibit the catalysis by silver. 

 Thallium resembles silver in the solubility of 

 its halogen salts, i. e., the fluoride is soluble 

 while the chloride and bromide are insoluble, 

 and similarly soluble chlorides and bromides 

 inhibit the catalysis by thallium while fluor- 

 ides do not. Thallium differs from silver in 

 that its cyanide is soluble and it was found 

 that hydrocyanic acid has only a slight inhib- 

 itory action on the catalysis by thallium and 

 this result is due to the fact that the metal is 

 dissolved and hence the action of hydrocyanic 

 acid on thallium is not at all comparable to 

 its action on silver. Using freshly cut shav- 

 ings of thallium the formation of the film on 

 treatment with potassium bromide can be di- 

 rectly observed. On the other hand, hydro- 

 cyanic acid accelerates the catalysis by copper 

 sulphate and ferrous oxide and also by finely 

 divided copper and iron. It was found that 

 if the salts of a given acid exert a retarding 

 effect on the catalysis by a given metal the 

 ammonium salt retards more than the cor- 

 responding sodium or potassium salt. This 

 is also capable of simple explanation. Am- 

 monium is a far weaker base than sodium or 

 potassium, and is, therefore, more easily re- 

 placed by the catalyzer. 



The ammonium salt thus lends itself more 

 readily to the formation of a film. Thus the 

 action of certain salts on the catalysis of hy- 

 drogen peroxide by metals is readily explained 

 when we take into account the simple and 

 well-understood chemistry of the substances 

 with which we are dealing. It is true that 

 the action of all inhibitors has not been ex- 

 plained as yet and in some instances undoubt- 

 edly other factors play a part, as has been 

 found in the case of ammonium sulphocy- 

 anate. The action of accelerators is not as 

 yet perfectly clear, but when the explanation 



is reached it will certainly take into consid- 

 eration more the chemistry of each individual 

 substance than the mere fact that they are in 

 the ionic state. In general the sodium salts 

 of the organic acids accelerate the catalysis. 

 In our opinion the hydrolysis of these salts is 

 to be taken into account as one factor in this 

 acceleration, since the alkalies promote the 

 decomposition of hydrogen peroxide and in- 

 crease its instability. When we state that a 

 thing is an anion or a cation we by no means 

 exhaust the chemistry of the ion as seems to 

 be sometimes inferred. An attempt to ex- 

 plain the action of inhibitors on the catalysis 

 of hydrogen peroxide by metals in terms of 

 the ionic theory as ordinarily employed in 

 physiological work leads to conclusions that 

 are entirely misleading. Thus ammonium 

 chloride inhibits the catalysis by silver and 

 thallium much more than sodium or potas- 

 sium chlorides. To conclude from this that 

 the ammonium ion is the inhibiting agent 

 would be entirely erroneous. It is the chlorine 

 in all cases that acts on the metal to form the 

 film and the ammonium chloride inhibits the 

 catalysis more strongly because the chlorine is 

 less firmly held. To state from such facts 

 that the cation retards the catalysis would 

 neither be expressing a fact nor offering an 

 explanation of the supposed fact. In a sub- 

 sequent publication* Neilson and Brown make 

 the following statement : ' In our work on the 

 effect of ions on the decomposition of hydro- 

 gen peroxide by platinum black, we obtained 

 results which may be explained by the assump- 

 tion that in general the anions exert a stimu- 

 lating action, and the cations a depressing 

 action, so that the action of a given salt de- 

 pends on whether the anion or cation is the 

 more powerful.' The writers fail entirely to 

 see the slightest suggestion of an explanation. 



It seems to be true that most chemical reac- 

 tions occur between substances in the ionic 

 state, and the necessity of the presence of 

 water for many chemical reactions has led 

 some chemists to assume that chemical inter- 

 action only occurs between ions. This is still 

 an open question. Even in so simple a case 



* Amer. Jour, of Physiology, Vol. X., p. 336, 

 1904. 



