The Germicidal Action of Metals, etc. 



79 



other meilium, and that in some direct way the metal arrests the growth or 

 actually brings about the death of the micro-organisms. 



Certain observations made by Prof. Barnes, and a recent paper by Barnes 

 and Shearer, have opened up the possibility of gaining a more direct 

 knowledge of the mechanism by which these metals act, and the present 

 series of observations owes its origin to Prof. Barnes. Barnes and Shearer 

 working with aluminium showed experimentally that aluminium foil in water 

 containing dissolved oxygen generated peroxide of hydrogen according to the 

 following hypothetical equation : — 



2AI + 6H2O + 6O = Al2(OH)6 + 3H202. 



Concerning the production of the peroxide tliey write as follows : — " We 

 placed pure aluminium sheet in ordinary pure distilled water open to the air 

 and thoroughly charged, and after standing for a few hours we applied the 

 well-known potassium iodide test for peroxide with marked success. Having 

 obtained evidence of the production of the peroxide, we found that the yield 

 could be increased by using considerable quantities of aluminium foil in small 

 pieces, and leaving it for two or three days in water, through which air 

 bubbled." They further showed that the production of peroxide of hydrogen 

 depended upon the presence of dissolved oxygen, and subsequently that zinc 

 acted in a manner similar to aluminium, and that with copper there was no 

 production of peroxide of hydrogen. 



The germicidal action of hydrogen peroxide is well known. It became, 

 however, a matter of interest to observe in the first place in connection with 

 those metals which in water gave origin to hydrogen peroxide, how far their 

 bactericidal properties bore relationship to the presence of the peroxide, and, 

 in connection with the metals causing no development of peroxide, whether 

 any cause could be determined for their activity. The problems to be 

 solved demanded the development of a series of experiments ; in the first 

 place, upon the maximal production of hydrogen peroxide through the 

 agency of the pure metals, and later the effects of the metal in water 

 containing dissolved oxygen, and lastly in oxygen-free water. 



After some preliminary investigation during which many experiments were 

 performed, the technique to be described was adopted, and, although some of 

 the results here made use of were obtained prior to the improved method of 

 investigation generally adopted, subsequent experiments showed them to be 

 sufiiciently accurate as compared with the newer method, the results varying 

 slightly in degree, but not in kind. The metals used in the experiments were 

 pure and were supplied by I'rof. Barnes. The water used was the Montreal 

 tap water, which is a soft alkaline water derived from the Ottawa Eiver, 

 containing variable, but in general small numbers of natural micro-organisms. 



H 2 



