Reéxamination of American Minerals. 51 
with red. It resembles serpentine, but hasa strongly argillaceous 
odor when moistened. 
Having reason to suspect that the substance was not perfectly 
homogeneous—from our first analysis not agreeing with Prof. 
Shepard’s,—various specimens were examined. The correct- 
~ of the supposition will be seen by est Nd the following 
results. 
1, a: 3. = 2 
Silica, 44°80 44-77 44:94 46°10 46°60 4474 441 
Alumina, 24°90 85°88 25°05 81-01 8515 20°98 20°64 
, 1 252 3:33 3°69 t a 
Manganese, -30 “30 iz tr. tr. tr. 
ime, *66 *b2 8-44 tr tr. 12:90 . 12°34 
Magnesia, ‘42 *b3 6°86 BO 50 8-48 5 
Potassa, 687 — 5°80 11:68 11:68 3713... 3:92 
3°60 tr. tr. —- tr. patel 
Water, 538 4:72 611 530 5:30 486 6°30 
99°94 10053 9888 99:13 99°96 99:90 
There is a remarkable agreement in the per-centages of silica. 
The mineral was found to lose about 2 per cent. of water by de- 
meealion. Some + aoe showed the presence of a small amount 
phosphoric acid. Nos. 1 and 4 were received from Mr. 8. W. 
Johnson No. 2 from Mr. Ne R. Horton, and the exact loom 
it is Diana , N. Y., No. 3 was received from Prof, Hume’ of 
Obutlesiee who obtained it from Prof. Shepard. 
The original analysis by Prof. Shepard gave, 
Bi 1 Fe H a 
47°68 41:50 5-48 4°83 tra 
This substance bears a close relation to ELAR T which 
from the variable proportion of its constituents, cannot be con- 
sidered a mineral but isa rock. Some of the specimens of dysyn- 
tribite give the composition of Pinite, but it is reasonable to sup- 
pose, that a mineral varying so much in its alumina, magnesia, 
lime and alkalies, may in different masses furnish a resemblance 
to a vast number of minerals. 
25. Gibbsite. 
Gibbsite was first described by Dr. Torrey * as hydrate of alu- 
mina. This composition, confirmed by Dewey and Thomson, was 
considered correct, until Hermannt announced the discovery of 
over 37 per cent, of ea eri acid in it, and that the mineral was 
a hydrous phosphate of alumina. 'To satisfy all doubts in this mat- 
ter, Prof. Silliman, Jr.,f examined it with direct reference to the 
occurrence of phosphoric acid, and in none of the specimens ex- 
amined, could he find more than a trace. Subsequently Mr. 
Crossley,$ of Boston, analyzed it, and his results confirmed the 
peas analyses of American chemists ; meanwhile gil 
N. Y. Med. and Phys. Journal, i, + J. m., xl, 32 
t This Jour., [2] vii, 411.  § This sg [2] ix, 408. |] Z. wy pr. he. xlyii, 1 
