220 W. J. Comstock—Chemical Composition of Uraninite. 
Art. XXVIII.—On the Chemical Composition of the Uraninite 
from Branchville, Conn.; by W. J. Comstock. (Contribu- 
tions from the Laboratory of the Sheffield Scientific School. 
No. LVIIL) 
nothing with which they could be confounded, and hence the 
purest material was available for analysis. A few crystals had 
a thin yellow coating, probably of uranium phosphate. The 
erystals were all octahedral in habit, in most the planes of 
the dodecahedron appeared, and ina few cases, those of the cube. 
The mineral is readily soluble in nitric acid, yielding a yellow 
solution, but it is not acted upon by hydrochloric acid. It de- 
crepitates on heating and gives off traces of moisture. When 
heated strongly in an open tube it has a very slight acid reac- 
tion on litmus paper. An analysis showed the mineral to have 
the following composition : 
. L Ai. Mean. 
U. = 81°67 81°33 81°50 
Pb = 4°01 3°94 3°97 
Fe = “41 89 -40 
i se 1337 13°47 13°47* 
H,O = “88 *88 
Total 100°22 
* For the oxygen, the determination in No. II is used, as it was made with 
greater care. 
The uranium, lead and iron were separated and weighed 
according to the ordinary methods. The water was driven bs 
by ignition and determined by absorption in a calcium chloride 
ube. The oxygen was determined by decomposing the min 
* This Journal, II, xvi, 35, July, 1878. 
