110 C. U. Shepard—Mineralogical Notices. 
Experiment 2.—A plate was treated in all respects as in No. 1, 
except that the application of the nitrate of mercury for remov- 
ing the developed image was made by yellow light. The plate, 
now showing nothing but a uniform yellow film, was carefully 
washed, and an iron developer, to which nitrate of silver and 
citric acid had been added, was applied. Jn this way the original 
image was reproduced, and came out quite elearly with all] its 
details. 
Now as every trace of a picture and all reduced silver had 
been removed by the nitrate of mercury, it is by this experi- 
ment absolutely demonstrated that the image is a purely physi- 
eal one, and that after having served to produce one picture, 
that picture may be dissolved off, and the same physical impres- 
sion may be made to produce a second picture by a simple ap- 
plication of a developing agent. ‘ 
Philadelphia, June 14, 1865. 
P. &.—Since the above was written, I have repeated the ex- 
periment with a pyrogallic development with similar results. 
Both the first and second developments may be made with an 
iron developer, or both with a pyrogallic. The experiment suc- 
ceeds without the least difficulty in either way. 
Art, XIV.—WMineralogical Notices ; by Prof. C. U. Soeparp. 
1. Syhedrite-—I have thus named, from its locality, a very 
retty green mineral sent me in small quantity by Dr. Thomas 
Idham, Geological Surveyor General of India. It has the fol- 
lowing properties: Hardness =3°5. Gravity =2:321. Massive; 
irregularly foliated in much-contorted individuals, resembling 
common varieties of massive highly crystalline dolomite. Color 
leek-green,—that of the purest Indian heliotrope. Translucent 
on the edges only. Luster vitreous. Cleavage in one direction 
very distinct. Brittle. Liable to alteration by exposure to the 
weather, when it loses its luster and cleavage, and assumes a pale 
greenish color, at the same time emitting an earthy odor if mois- 
tened. 
Before the blowpipe it swells up slightly and undergoes éasy 
wished to as muc 
for an analysis by Mr. Tyler, I had but six grains to submit to a 
qualitative examination. Nevertheless, I kept as accurate an ac- 
t 
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