219 
1887.] Prof. J. B. Hay craft on the Sense of Smell. 
sent, the colour, taste, and smell sensations alter in character in the 
manner that I have described. 
2. On the Physics of Noise. By Professor Crum Brown. 
[Abstract.) 
The noises considered in this paper are uniform, continuous noises, 
such as the fricatives of articulate speech : f, 0, s, y, &c. These 
sounds are considered by the author to stand in a similar relation to 
musical tones as lights with continuous spectra do to lights with 
bright-line spectra. Methods were proposed for analysing these 
uniform continuous noises, and also for imitating them by synthetic 
means. 
3. On the Physical Properties of Methyl-Alcohol. By 
Professor Dittmar and C. A. Fawsitt, Esq. 
4. On the Instability of the Double Sulphates 
M"S0 4 ,B' 2 S0 4 4- 6H 2 0 
of the Magnesium Series. By W. Dittmar. 
By a number of observations made incidentally in the preparation 
of two of the double salts referred to in the heading, namely, the 
compounds of sulphate of potash with sulphate of magnesia and 
sulphate of ferrous oxide respectively, I had long come to suspect 
that these two salts at any rate are not perfectly stable in opposition 
to water. To settle the question, I have caused Mr James Pobson and 
Mr Andrew Hodge, two young chemists working in my laboratory, 
to inquire into the matter by systematic experiments. These were, 
in general at least, conducted according to the following scheme : — 
Starting from a known weight of sulphate of potash, this was dis- 
solved in a proportion of hot water,* less than sufficient to hold the 
intended double salt in solution after cooling ; there was then added 
a known weight of the di-valent sulphate amounting to exactly 1 or 
* In the case of FeS0 4 the water was acidified with a few drops of sulphuric 
acid to prevent precipitation of ferric compounds. 
