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, to the College Museum, by Profes- 

 sor Radice. It occurs in detached mammillary and wrinkled 

 masses, sometimes larger than a walnut, and pellucid in a 

 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 

 conchoidal fracture. 



" 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 

 lo 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, 



Silex, 97.48 



Water, 2.52 



results which correspond accurately with the formula 

 I5SO3, 2H0. 



" Beudant says, that in the case of the transparent opals, 

 by which he, of course, means the hyalites, 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, 



