Improvement in Photography. 353 
the decomposition upon the surface of the solid metal. _ It occur- 
red to us as a possibility that the iodide formed in the usual 
manner, by exposing a plate over the vapor of iodine, might 
perhaps give up its silver to chlorine, and thus produce the de- 
sired coating. This impression was not verified in our first ex- 
periments, owing to a cause which will presently be noticed. 
Perseverance, however, at length brought itsreward. By varying 
in every possible manner, the circumstances of the experiment, 
we succeeded in producing a surface so exquisitely sensitive to 
the action of light, that the image of an illuminated object was 
formed upon it in the camera in a space of time almost inap- 
preciable. 
The following is the process by which this result is obtained. 
Let the plate be prepared in every respect as if an impression 
were to be taken according to the method of M. Daguerre. Let 
it be then exposed for the space of half a minute to the action of 
chlorine gas, diluted with common air to such a degree that it 
may be inhaled without any particularly unpleasant sensation. 
It will then be found so extremely sensitive, that on being 
placed in a camera, with an aperture such as is commonly em- — 
ployed in taking miniature portraits, an impression will be pro- 
duced upon it in the smallest time in which it is possible to 
remove and replace the screen. The completion of the picture 
over mercury is effected in the usual way. 
A plate thus chlorized, on exposure to light almost immedi- 
ately assumes a very deep violet color, nearly approaching black. 
The mercury is not directly tarnished, and in this state the pic- 
ture is even more beautiful than after being washed with the 
hyposulphite of soda. But without this washing it cannot be 
preserved. 
M. Daguerre has announced that he is able to take images of 
_ objects in an instant of time. I have not seen any statement of 
his method. Some of the artists in the Atlantic cities have 
been equally successful. Their process is not that which I have 
here described. 1 suppose that I am acquainted with the mode 
of preparation which they employ ; but as it was communicated 
to me under an injunction of secrecy, before 1 had discovered it 
myself, although I had actually employed it unskilfully, and 
therefore without complete success before, 1 can say nothing of 
it here. It will, without doubt, soon be made public, if it is not 
Vol. xt1, No. 2.—July-Sept. 1841. 45 
