82 



Dr. A. C. Rankin. 



[June 12, 



follow. The work of Clarke and Gage would also point to the fact that it 

 was not so. To investigate the point, however, the following experiment was 

 performed : — 



Aluminium, zinc, and copper were bubbled for a period of one hour in tap 

 water, and the water was then withdrawn into a sterile bottle and allowed to 

 stand overnight. These three portions of water were then inoculated 

 with B. coll ; plates were made immediately, and again in one hour. The 

 results are given below : — 



Metal. 



Water. 



Time. 



1st plate, 

 1/20 CO. 



2nd plate, 

 1/20 c.c. 





c.c. 



hour. 







Aluminium... 50 grammes ... 



150 



1 



Innumerable 



Innumerable. 



Zinc 50 



150 



1 



J' 





Copper 50 „ 



150 



1 





Slight reduction. 

 • 



These results conform to the previous experiments, and were to be expected. 

 Others have shown that small quantities of copper may at first inhibit the 

 growth of B. coli, but that subsequentlj' the results are very similar to those 

 obtained when B. coli are added to sterile water in glass vessels and allowed 

 to stand. The results with aluminium and zinc show that the amounts of 

 these metals in solution exert no bactericidal action ; that the small 

 quantity of peroxide of hydrogen still present exerts no effective action. 



Froduciion of Peroxide of ITi/drogen. — Quantitative tests of the amount of 

 available oxygen in the water after air liad been bubbled tlirough for one hour 

 gave the following figures : — 



With zinc — 



(1) 0-318 per cent, by volume, equivalent to 0'00096 per 



cent, hydrogen peroxide by weight. 



(2) 0'299 per cent, by volume, equivalent to O'OOOQO per 



cent, hydrogen peroxide by weight. 



With aluminium — 



(1) 0'252 per cent, by volume, equivalent to 0 00076 ])er 



cent, hychogen jicxoxide by weight. 



(2) 0-195 per cent, by volume, equivalent to 0-00059 per 



cent, hydrogen peroxide by weight. 

 With copper None. 



I do not need to emphasise the point that these amounts of peroxide per 

 cent, can have little germicidal olfect. Obviously the results to be noted below 



