9 
Prof. Joy exhibited some of the double Iodide of Silver 
and Mercury, received from Prof W. Gibbs. It is a yellow 
salt, and one of the most sensitive to heat known, turning red 
on warming, and returning to its original yellow color on 
cooling, thus changing tint very much after the manner of 
Bin-lodide of Mercury. 
Apmil 18, 1870. 
The President.in the chair. Twelve persons present. 
Prof. D. S. Martin, exhibited a specimen of Copper 
Pyrites from Central Texas. This ore is worked, and re- 
ported to be very rich, yielding as much as 62 per cent. of 
copper; and is smelted with great ease. It is frequently 
found as a pseudomorph replacing wood. 
The President remarked upon this specimen, that the 
deposit from which it was procured, was a very extensive 
one, being found in the same horizon in New Mexico and 
Arizona. These deposits have been very extensively worked 
by the Spaniards, and some of the ancient workings are at the 
present time in a state about as perfect as when abandoned 
by these ancient miners. They are now the abode of multi- 
tudes of bats. Specimens of wood ten feet long, and two 
feet in diameter occur, in which the woody fibre has been 
completely replaced by the Pyrites, besides which are found 
accumulated at the bottom of the cliffs, laree quantities of 
silicified wood. 
Prof. C. A. Seely remarked upon the occurrence Of Nitre 
in the caves in Arkansas, and attributed its origin to the ex- 
crements and remains of the bats inhabiting those places. 
' The President stated that these caves were found in many 
places in the West, and it was to be regretted, that as yet, no 
systematic examination of them and their contents had been 
inacle. 
