354 On two Decomposed Varieties of lolite. 



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. 



Much care is necessary to avoid an excess of chlorine. The 

 principal cause of our early failures arose from an error of this 

 kind. One may easily determine, with any apparatus, the time 

 and quantity necessary, by laying a plate over the aperture and 

 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 pro- 

 cess of preparation. 



Tuscaloosa, July 1, 1841. 



Art. XI. — On two decomposed varieties of lolite; by Charles 

 Upham Shepard, Professor of Chemistry in the Medical Col- 

 lege of the State of South Carolina. 



1. Finite of Haddam. — This mineral is mentioned in Cleave- 

 land's Mineralogy on the authority of Prof. Silliman, as occur- 

 ring at Haddam, (Conn.) where it was probably noticed as early 

 as the discovery of the chrysoberyl, along with which it was 

 first found. It presents itself most commonly, in small foliated 

 masses of a dull bluish green color, disseminated through the 



