1887 .] Prof. J. B. Hay craft on the Sense of Smell 
217 
If now an atom of hydrogen of the ammonia be replaced by methyl, 
the ammonia hands are still visible, but they are shifted somewhat 
towards the red end of the spectrum. Replacing the hydrogen by 
the larger molecule of ethyl, the hands are seen to pass still nearer 
to the end of the spectrum. 
hTH 3 Ammonia 
CH 3 .NH 2 Methylamine 
C 2 H 5 .NH 2 Ethylamine 
Produce hands which shift to red end of 
spectrum in ascending the series. 
In the same way we find that common alcohol possesses absorp- 
tion bands, seen also in the higher members of the group, but shift- 
ing towards the red end of the spectrum in ascending the group. 
C 2 H 5 .OH Alcohol \ Produce hands which shift to the red 
C 3 Hf.OH Propyl alcohol > end of the spectrum in ascending the 
C 4 H 9 .OH Butyl alcohol I series. 
In the case of coloured acids, such as chromic and picric acids, 
the salts too are coloured. If the hands of these acids he examined, 
and if they he then converted into salts, the absorption will shift 
towards the red end of the spectrum. It seems that the molecule, 
having a certain vibrational character depending upon its structure, 
is weighted by the added metal, the vibrations of which do not 
probably appear at all in the visible spectrum, and, in consequence, 
its pitch is lowered. If an odorous substance like acetic acid be 
combined with another odorous substance, it is generally possible 
to detect the two intermingled sensations in the compound. Ethyl 
acetate is ethereal and acetous at the same time. Allyl sulphide is 
like allyl alcohol, and has the odour of a sulphur compound as well. 
In this case it is probable that those vibrations in each substance 
which produce smell are not so much lowered in pitch by the new 
substance with which they are combined as to change the character 
of the sensations they are each capable of producing. The am- 
monia vibrations are shifted towards the red end of the spectrum in 
methylamine, but not enough to produce another sensation. In 
other compounds of two odorous substances it may not be possible 
to distinguish the original odours, and for the reason that the pitch 
has shifted, as we have seen it often does, so as to produce quite a 
different sensation. 
