1887.] Prof. J. B. Haycraft on the Sense of Smell. 
213 
Group YII. 
Element. 
Potassium Compound. 
Formyle Compound. 
F 
Salt and saline. 
Cl 
Salt, saline, bitter. 
Characteristic odour of chloroform. 
Mn 
Br 
Salt, saline, and bitter. 
Intermediate odour. 
I 
Saline, bitter. 
Characteristic odour of iodoform. 
Potassium fluoride is salt — like common salt in taste. In addi- 
tion it is slightly saline — like nitre. Chloride of potassium has a 
suspicion of a bitter taste as well, and so has potassium bromide. 
Potassium iodide has lost the taste of common salt, being a saline, 
and bitter. 
So far, then, we have seen that the power of producing taste 
is a property or function of elements. Our knowledge of matter 
is derived from its power of producing sensation within us. 
In the case of sight and hearing we have associated quality in 
sensation with the kind or character of the vibrating stimulus. If 
it can be shown that elements belonging to the same “ group ” are 
capable of vibrating in a way which is similar or related to one 
another, then we have grounds upon which to draw an analogy 
between smell, taste, sight, and hearing. 
On account of our incomplete knowledge of the ultra-red and 
ultra-violet regions of the spectrum, a final answer to this question 
cannot perhaps be given. Only rough indications are to hand, but 
these point in the same direction. 
The chlorides of the alkaline earths have spectra which are nearly 
related. The spectra of Group I. are not dissimilar, especially 
potassium and rubidium, with the five groups of lines. Then, again, 
the chlorides, bromides, and iodides of calcium and barium are 
similar, the lines shifting towards the red end of the spectrum in a 
way which is nearly proportional to the increase of atomic weight. 
The colour of a substance is an index to the pitch of the vibra- 
tions of its molecules. In a paper on the colour of chemical 
compounds recently published in the Philosophical Magazine 
(July 1874), Professor Carnelley demonstrated the existence of a 
relationship between the salts of the same group of elements 
in respect to colour. The salts, say the chlorides, of a group of 
