1887 .] Prof. J. B. Hay craft on the Sense of Smell. 
209 
is met with, this difficulty, that there is no nomenclature familiar to 
every one. Hundreds of terms expressing the well-known colours of 
familiar objects, enable one to describe by a single term almost any 
tint and shade. We have cardinal, rose, magenta, maroon, carmine, 
crimson, scarlet, and a dozen other shades of red alone, and all of 
these can be expressed by words. The smells, however, and espe- 
cially those of the chemist’s museum, are so unfamiliar, and often so 
peculiar, that we are forced to speak of them simply as the odours of 
the substances which produce them, or to say that they are like, 
though never identical, with that of some other and better known 
substance. 
USTo two observers quite agree in their descriptions of a given odour, 
and the information readily at hand in the text-books, but culled 
from a hundred sources, is therefore not reliable. I have, for this 
reason, availed myself freely of the kindness of my colleague Prof. 
Tilden and my friend Prof. Ramsay, who have placed at my disposal 
their private collections of chemical compounds. In almost every 
case the description of a smell given in this paper is derived from 
personal observation. 
In the first place, let us study those few substances found among 
inorganic compounds which have distinct smells. It is well known 
that many substances, like arsenic, chlorine, sulphur, bromine, and 
their compounds, have characteristic odours. Can we associate the 
odours of these substances with any chemical or physical properties 
they may possess, and show that when similar odours are produced 
by two or more substances, then we have some similar chemical or 
physical property present at the same time ? 
In recent years a remarkable discovery of Hewlands has opened 
up a fresh point of departure in the science of chemico-physics. 
His observations led him to formulate a law which he termed the 
law of octaves. Lothar Meyer, Mendel ejeff, and Carnelley, extending 
his work, have shown that the “periodic-law,” as it is now called, is 
one of vast application and importance. The nature of this periodic- 
law is now so well known, thanks to the many recent publications 
of Professor Carnelley, that it would be superfluous to attempt more 
than roughly to sketch out its main features. If we arrange the 
elements in the order of their atomic weights, beginning with that 
which has the lowest, and passing to that which has the highest, we 
