521 
ries being devoted to subjects more purely geometrical ; as the 
First Series (already printed) relates chiefly to others which 
are of a more algebraical character. 
Dr. Apjohn read a paper on the composition and optical 
properties of a variety of hyalite, from Mexico. 
‘* This mineral,” he observed, ‘‘came into my possession as 
___ Professor of Mineralogy to the University, having been pre- 
sented, through Mr. Ball, tothe College Museum, by Profes- 
sor Radice. It occurs in detached mammillary and wrinkled 
masses, sometimes larger than a walnut, and pellucid ina 
high degree, It is harder than glass, but is scratched by steel, 
and, from an experiment very carefully made, was found to 
have the specific gravity of 2.1016. It is much more frangi- 
ble than quartz, but when broken exhibits something of the 
— eonchoidal fracture. 
4 *¢ The different properties just enumerated belong also to 
other well-known varieties of hyalite; and, notwithstanding 
its occurring in detached glassy drops of unusual size, little 
hope was entertained that a chemical examination of it would 
conduct to any new result. Upon, however, subjecting it to 
_ experiment, this anticipation was not verified, for it was found 
to contain much less water than any variety of hyalite whose 
composition has been recorded. Thus, as the mean of four 
experiments scarcely differing from each other, it yielded, 
Bee, RE bon niot. oosie@F.48 
Waterstiuntm dat 29 sto BH2 
results which correspond accurately with the formula 
. 15S0O,, 2HO. 
_ * Beudant says, that in the case of the transparent opals, 
__ by which he, of course, means the Ayalites, the loss by calcina- 
tion amounted always, in his experiments, to from eight to ten 
per cent. ; while, in the case of the semiopaque opals, the vola- 
tile matter expelled by heat varied from five to seven per cent. 
And in two analyses of hyalite, the details of which he gives, 
