486 
PROFESSOR TYNDALL ON DUST AND HAZE. 
who stated to me that it was given to the medical officer of his department by 
a person who could be relied upon. In looking through the Journal this month, 
I find that Dr. Ogden’s (Royle) is almost identical with mine, a copy of which 
I forward. I find nearly all the recipes for chlorodyne contain ol. menth. pip. 
I am of opinion that the smell similar to peppermint is produced by the action 
of the perchloric acid upon the chloroform, and that Browne’s chlorodyne does 
not contain mint, and I also am of opinion that it does contain tincture of In¬ 
dian hemp, which produces the green coloriition Mr. Smith alludes to. I find 
in making chlorodyne a great deal depends upon the colour and thickness of the 
theriaca used, some being much darker and thicker than other sorts used. 
Chi or of or mi. 
/> 1V 
Sp. Vin. Rect. 
5T 
Morph. Hydrochlor. . 
gr. vi ij 
Acidi Perchlor. .... 
gtt. X 
Tinct. Capsid .... 
5S3 
Tinct. Cannabis Ind. . . 
5i 
A cid. Hydrocyan. (Sclieele’s) 
gtt. xij 
Theriacse. 
5h 
Landport, January 11, 1869. 
PROFESSOR TYNDALL ON DUST AND HAZE. 
The Friday-evening lecture season at the Royal Institution commenced on 
the 21st of January, with a lecture by Professor Tyndall on “Dust and Hazed' 
The chair was taken by the President, Sir Henry Holland, who was supported, 
not only by the elite of the scientific world, but also by many other dis¬ 
tinguished men, including the Right Hon. W. E. Gladstone, Earl Granville, 
Sir Edwin Landseer, and the Dean of Westminster. 
The lecturer commenced by referring to the fact that a sunbeam, passing 
through a darkened chamber, reveals the existence of certain particles floating 
in the air. This phenomenon he was unable to show his audience, since he had 
not at his command a ray of solar light; but in the electric light he had a 
“ domestic sun,” by the aid of which he could demonstrate the presence of this 
dust in the atmosphere of the lecture theatre. Some time ago he had occasion 
to make experiments upon the action of light on vapours, when this air-dust 
was found to cause so much annoyance that it became necessary to remove it. 
The air was passed over sulphuric acid and caustic potash, with a view of freeing 
it from aqueous vapour, and carbonic acid, but these operations failed to free 
it from the dust. Various methods of getting rid of it w r ere tried, but they all 
failed, until at last the lecturer somewhat unexpectedly found that the atmo¬ 
sphere could be deprived of the floating particles by allowing it to pass over the 
tip of a spirit-lamp flame before it entered his experimental apparatus. This 
indicated that the particles were combustible and organic. A more efficient 
means of burning the dust was therefore fitted up. A platinum tube, contain¬ 
ing platinum-gauze, was intensely heated, and through this air was allowed 
slowly to stream : under these circumstances the dust was entirely removed. 
But it might, perhaps, have been merely mechanically retained by this gauze; 
the experiment w r as accordingly repeated after the tube had been allowed to 
cool. Now, however, no separation of the particles was effected; the dust, 
therefore, was destroyed solely by the action of the heat. The lecturer men¬ 
tioned that he had attempted to bum the particles in the focus of a concave 
