340 



GERMICIDAL ACTIVITY OF KUCALYPTUS OILS, 11., 



dilutions. For this reason, it would be a mistake to employ 

 ordinary tap- water when making dilutions, as its slight alkalinity 

 would tend to reduce the germicidal efficiency. 



Since phenol behaves as a weak acid, it is likely that its 

 activity will be enhanced in the presence of dilute acid. A pre- 

 liminary test showed that this was so, for with 10° of acidity, 

 as acetic acid, dilutions up to 1 : 200 were germicidal in 30 

 minutes. A test made at the same time with 11° (corrected) of 

 alkalinity as sodium bicarbonate gave normal numbers up to an 

 hour, and at four hours the lethal dilution was 1 : 180, as against 

 1 : 140 with neutral water. Alkali itself has no action when 

 used in small amounts, for a control test showed that water with 

 22° of alkalinity as sodium bicarbonate was inactive in four 

 hours. 



Thus the addition of alkali or of acid to the water used for 

 dissolving the phenol, increases the efficiency, and of these, the 

 acid is the more powerful. 



The effect of acidity upon the action of phenol was confirmed 

 in the following experiment. Solutions of acetic acid were pre- 

 pared to give l u and 10° of acidity, but when the pipette was 

 checked it was found that the number of drops per gram differed 

 with the strength of the acid. Solutions of _. strength gave 72 

 drops per gram, while those of ^ gave 90 drops. The actual 

 acidity was therefore weaker. 



Table xx. B. co/i communis. 



— or weaker. 



