894 Proceedings of Royal Society of Edinburgh. [sbbs. 
Evaporation of Musk and other Odorous Substances. 
By John Aitken, LL.D., F.R.S. 
(Read July 10, 1905. MS. received July 17, 1905.) 
In scientific literature the evaporation of musk has a considerable 
interest. Almost every writer on the divisibility of matter cites 
it as an instance of the extremely minute division of which 
matter is capable, our sense of smell enabling us to detect 
a more minute quantity of this form of matter than can be 
detected of any other kind of matter by any of the modern refined 
methods, such as the spectroscope, or chemical processes. It is 
possible we may shortly have to modify this statement, as 
extremely small quantities of some kinds of matter can be de- 
tected by their radio-activity ; but, so far as I know, no reliable 
numerical values have been obtained in this direction. 
To give an idea of the extreme minuteness of the particles of 
musk that are capable of affecting our sense of smell, the following 
figures may be given. Leslie, in his Natural Philosophy (1823), 
says, referring to a grain of musk that had perfumed a room for 
twenty years, “ that at the lowest computation the musk had been 
subdivided into 320 quadrillions of particles.” The following- 
table, for which I am indebted to Dr Gordon Blackheath, gives 
a more recent estimate of the amount of musk that can be 
detected by its smell, and it will be noticed that it is not so small 
as Leslie’s estimate. The table also shows the smallest amounts 
of some other kinds of matter that can be detected by the most 
refined methods. 
Delicacy of the Sense of Smell compared with that of 
SOME OF THE MOST DELICATE OBJECTIVE TESTS. 
Substance. 
Smallest part of a 
Gramme detected. 
Re-agent. 
Authority. 
Musk 
Iodoform . 
Sodium 
Lithium . 
Nitrite 
0-000,000,000,000,000,01 
0-000,000,000,000,01 
0-000,000,000,03 
0-000,000,001 
0-000,000,001 
Sense of Smell . 
> J 
Spectroscope 
5 J 
Ilosvay’s re-agent 
Berthelot 
Bunsen k KirchofF 
Bunsen 
Warington 
