354 On two Decomposed Varieties of Iolite. 
already known. I believe, at any rate, that the chloride coating 
is more sensitive than any other which has yet been used. 
This discovery has opened a new field of experiment, in 
which we are now actively engaged. The results may be 
communicated hereafter. | 
It appears to us that the lights produced by this process of 
preparation are much finer and smoother than those of the ori- 
ginal process of M. Daguerre. Some idea of the quickness of 
the camera operation may be formed from. the statement of the 
fact, that a man walking may be represented with his foot lifted 
as about to take a step. 
The quantity of chlorine necessary to produce the effect is 
exceedingly minute. In our early experiments we employed a 
quart bottle of the gas, opening it in a deep box, and leaving out 
the stopper while deliberately counting twenty. Replacing then 
the stopper, the plate was laid for half a minute over an opening 
in the top. After fifty experiments the gas in the bottle seemed 
not to have lost any of its original intensity of color. We have 
better arrangements at present in preparation. sauce 
Much care is necessary to avoid an. excess of chlorine. The 
principal cause of our early failures arose from an error OF ! 
kind. One may easily determine, with any apparatus, the time 
and quantity necessary, by laying a plate over the aperture a0 
drawing it partially off at intervals... The action of the gas will 
then be greatest, of course, upon the part longest exposed. ‘Too 
much care cannot be taken to exclude the light during the pr 
cess of preparation. eR 
Tuscaloosa, July 1, 1841. 
s; cy gee 
Arr. XL—On. two decomposed varieties of Iolite; by OHARt®® 
Uruam Sueparp, Professor of Chemistry in the Medical Gol- 
lege of the State of South Carolina. ’ 
1. Pinite of Haddam.—This mineral is mentioned in CLEave* 
Lanp’s Mineralogy on the authority of Prof. Siunuiman, as 0ce 
ring at Haddam, (Conn.).where it was probably noticed as eatly 
as the discovery of the chrysoberyl, along with which igre 
first found. It presents. itself most commonly, in small foliat 
masses of a dull bluish green color, disseminated through the 
