1904-5.] Dr Aitken on Evaporation of Musk. 899 
other substances — that it is gaseous particles from the musk that 
act on our sense of smell. 
In confirmation of these results some other experiments were 
made. It was thought that if musk passes into the air as a gas 
or vapour that it would be able to pass through a quantity of 
cotton-wool sufficient to stop all dust-particles. To test this, part 
of the apparatus shown in the figure was used. The air was first 
passed over the musk, then through the cotton-w T ool filter, with 
the result that the perfume came freely through the cotton-wool. 
It did not come just at first ; but after pumping a short time the 
scent became quite distinct, apparently as strong as when not 
passed through the cotton-wool. Some of the gas which first 
entered the filter was trapped and held by the wool, but the 
wool soon became sufficiently saturated to allow the musk vapour 
to pass. The trapped vapour remained in the wool and could 
easily be detected afterwards. 
Having the apparatus arranged for testing the musk, it was 
thought advisable to test some other odorous solid substances ; 
camphor and naphthalene were accordingly experimented with. 
They both acted like musk and gave no nuclei of condensation, 
and the gas or vapour from both passed easily through cotton- 
wool ; so we may conclude that they, like musk, evaporate in 
gaseous form. 
It is intended to test a number of other solid odorous bodies 
to see if any of them give any support to the idea that they give 
off their perfume in solid particles. 
Note added 27th July . — Since the above paper was read on 
10th July, a number of other odorous substances have been 
tested. The cloudy condensation method of testing was used in 
all cases, as it seems to be the most satisfactory, and definite 
results were obtained by it ; whereas filtering through cotton-wool 
and diffusion tests are at times uncertain owing to the sensitive 
surface — the nostrils of the observer — not always giving a definite 
answer, especially when fatigued ; and there is the further risk of 
subjective sensations interfering with the correctness of the results. 
Diffusion tests made with ordinary porous cells are somewhat 
unsatisfactory, owing to some of the vapour being condensed in the 
