THE 
LONDON, EDINBURGH anv DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. 
(THIRD SERIES.] 
MARCH 1843. 
XXIII. On the rapid Detithonizing Power of certain Gases and 
Vapours, and on an instantaneous means of producing Spec- 
tral appearances. By Joun W. Drarver, M.D., Professor of 
Chemistry in the University of New York*. 
Fok some time after I was acquainted with the phaenomena 
mentioned in the last paper communicated in this Journal,+ 
and there referred to radiation, I was led to attribute them to 
a peculiar property which certain gases and vapours possess, 
of which I propose now to give a detailed description. 
This property is a power of effecting a very rapid detitho- 
nization of surfaces that have been powerfully tithonized. 
It affords the means of instantly procuring spectral appear- 
ances of external forms. 
Referring now, in the first place, to the analogies of caloric: a 
body which has been warmed cools down to a temperature that 
is in equilibrium with that of objects around in several different 
ways, by radiation, by currents in the air, and often by direct 
conduction, each of these tending to produce the same result, 
A sensitive surface, which has been disturbed by exposure 
to the daylight or lamplight, has the quality of restoring itself 
to its primitive condition when kept in the dark. Daguerre 
noticed this in the case of certain resinous bodies; other ex- 
perimenters have likewise proved that it takes place with some 
varieties of the ordinary photogenic preparations. I have found 
that it holds in the coloured films on the surface of silver, 
Much of this effect is due, as I have endeavoured in the 
paper above quoted to show, to a direct escape of dark rays 
by a process analogous to radiation; but much also is due to 
a hitherto unknown power, possessed by electro-negative gases 
* Communicated by the Author. 
t 5. 3. vol. xxi. p. 453: see also p. 131 of our last Number.—Ep. 
Phil. Mag. S, 3. Vol. 22, No. 144, March 1843. M 
