90 GERMICIDAL ACTIVITY OF EUCALYPTUS OILS, i., 



Table viii. — Iodide reaction of neutralised oils. 



E. dives, crude 



E. cinerea, rect. 



E.an$t r></ ia»a(Bra,k\wood) 



Time in seconds. 



Untreated. 



37 



7 



45 



Neutralised 

 with lime 



300 

 15 



with 

 Na 2 C0 3 



ISO 



Treated witl 

 sodium bisul- 

 phite, then 

 with lime. 



over 3,600 

 540 



The lengthening of the time of reaction certainly points to 

 the acidity having some influence upon the test. If, however, 

 the problem is attacked in another way, viz., by adding acid to 

 a feebly-reacting oil, it is found that the acid has no influence. 

 The crude oil of E. polybractea had an acidity of 4°, and gave the 

 reaction in 80 seconds. A quantity had been acidified witli 

 acetic acid seven days previously and had increased in its toxicity 

 towards the staphylococcus. The acidity was 95°, but the time 

 of reaction was the same as with the original oil, viz., 80 seconds. 

 We must conclude that the lime or the sodium carbonate, used 

 in neutralising the oils, removes much of the substance which 

 gives the iodide reaction. 



When considering the activity of the oils, there is no reason 

 for separating the rectified from the commercial. They are no 

 less germicidal than the crude oils, and indeed some of the recti- 

 fied oils were among the most active. Acidity may be developed 

 in the oils by aeration during a considerable period of time, and 

 concomitantly an amount of iodide-reacting substance may be 

 formed, but no relation was found to exist between the acid and 

 the ozone-like oxidising substance. Neither was there any rela- 

 tion between the iodide reaction and the bactericidal activity, 

 so that the iodide test is of little importance in determining the 

 bactericidal power of the oils. 



The Activity of the Vapours of the Oils. 

 The vapours of the Eucalyptus oils are supposed to possess a 

 disinfecting action, and some experiments were made with them 



