1909.] The iiermicidal Action of Metals, etc. 



83 



are not due to the mere presence of peroxide, but are due to some action 

 with which is associated the production of the peroxide. 



Germicidal Effect of Aluminium. — Aluminium strip cut into small squares 

 and cleaned was then experimented with. The metal, in various proportions 

 by weight, was bubbled with water containing B. colt. The results are shown 

 below : — 



Quantity of metal. 



Water. 



Time. 



1st plate, 

 1/20 c.c. 



2nd plate, 

 1/20 c.c. 



Peroxide. 





c.c. 



hour. 









Aluminium, 125 grammes 



150 



1 



Innumerable 



1 colony 



Present. 



100 



150 



1 



)i 



5 colonies 





75 „ 



150 



1 



n 



1 in 48 hrs. 





50 



150 



1 



)) 



1 



Slight trace. 



25 



150 



1 





Many 



25 



150 



1 



J» 







The first two experiments in the series were performed prior to a change 

 in technique, and it was subsequently shown that 50 grammes of aluminium 

 caused, depending upon the cleanliness of the metal, a good production of 

 peroxide of hydrogen, and would generally give a plate free from colonies. 

 A fair amount of peroxide of hydrogen is formed and a hydrate is thrown 

 down. The hydrate has no opportunity of sedimenting, the bubbles of 

 air keeping it constantly in motion and thoroughly mixed with the water. 

 In taking the test water, therefore, the hydrate is thoroughly mixed with 

 the water, thus excluding the possibility of live organisms being entangled in 

 the precipitate and carried down with it, and thus not appearing on the 

 plates. Quantitative tests for aluminium in solution showed only traces of 

 the metal present. 



Germicidal Effects of Zinc. — A series of experiments similar to those 



performed with aluminium were carried out with granulated zinc. The 



Metal. 



Water. 



Time. 



1st plate, 

 1/20 c.c. 



2nd plate, 

 1/20 c.c. 



Peroxide, 





c.c. 



hour. 





hours. 







150 



1 



Innumerable 



. 24 none 













48 a few 



Strong. 



„ 100 



150 



1 





24 none 











48 one 





» 75 „ 



150 



1 



») 



24 none 













48 tliree 



Fair. 



.> 50 .,, 



150 



1 





24 none 













48 two 





„ 25 „ 



150 



1 





24 six 





10 









48 twenty-four 



Slight. 



150 



1 



91 



24 thirty 





