PHYSIOLOGY OF OLFACTION 55 



centration necessary for the olfaction of a number of 

 alcohols. These determinations have been recorded in 

 millionths of a gram per liter of air and are given 

 in Table II. 



Passy 's determinations indicate that the lower alco- 

 hols have relatively faint odors, but that the higher 



Table II. 



Minimum concentrations for olfaction, in millionths of a gram of alcohol 



per liter of air (Passy, 1892c). 

 Alcohol Primary Secondary Tertiary 



Methyl 1000 



Ethyl 250 



Propyl 10 to 5 40 



Normal Butyl 1 20 to 10 



Isobutyl 1 



Normal Amyl 40 to 20 



Active sinistral Amyl 0.6 



Inactive Isoamyl 0.1 



Caprylic 0.005 



members of the series are fairly comparable with, for 

 instance, the essential oils. A determination for ethyl 

 alcohol by Parker and Stabler in 1913 showed that this 

 alcohol could be detected only to a concentration of about 

 5.75 milligrams of alcohol per liter of air. The smaller 

 amount found by Passy, namely 0.25 milligrams per liter 

 of air, is believed by these authors to be due to odorous 

 impurities that were found by them in certain ethyl 

 alcohols and that may have been present in those tested 

 by Passy. 



Some of the more striking determinations by Allison 

 and Katz (1919) are reproduced in Table III. 



Here it will be noted that the most active mercaptan 

 tested, propyl mercaptan, is detectable at a concentra- 



