24 OC. M. Wetherill on the Crystalline Nature of Glass. 
No. 7. Plate glass (microscope slide). om feo when 
Ver 
etched, srestston the same appearance as N ery small 
scicular crystals distributed sparsely over the Bold of view cOuld 
e seen 
No. 8. Three specimens of thin glass covers for microscopic 
objects. The etching of these was very uniform. Numerous 
add extremely minute needle-shaped sey stats requiring a high 
power for their definition, were observed. 
No. 9. Green bottle glass (two specimens). In these the crys- 
tallization was different from that of the former examples. In 
some places the etching was granular, asif small and short erys- 
tals had been removed by the acid. In other places blade-shaped 
crystals were marta these had a tendency to unite in star- 
like groups, as in snow. Upon one portion of the plate a few 
small squares and srianglod (insoluble in water) were seen 
No. 10. Two specimens of Bohemian glass combustion-tube 
etched upon the inside. These yielded a granular, very regular 
etching, and presented a very delicate ground glass appearance, 
which was resolved by the microscope into small crystalline ta- 
blets or scales, apparently reno of crystals. 
No. 11. Bohemian beaker glass; two specimens, of which one 
was attacked upon the outside, and the other upon the inner sur- 
face of the vessel. Small acicular crystals, resembling those 
No. 1, but better defined, and a few squares, triangles and tra rape. 
zoids were detected. 
No. 12. Lead glass tubing ; two specimens, etched upon the 
inside. — action of the solvent was energetic. The etching 
was granular, with numerous short and minute needles, requir- 
ing a — soi of the microscope for their definition. 
_ Nod A portion of a soda glass flask etched upon the in- 
This was corroded very readily and yielded plenty of 
po eigenen in appearance those of No. 1 
No. 14. Lead glass; inside surface of a matrass. ‘The ‘action 
of the iydrlluone acid upon this specimen was energetic. The 
S presen e appearance of con ees broken tablets, 
with here and there a needle-shaped cry 
The acid employed in the naa a gave no etching when 
dropped upon the different surfaces of a clear transparent quartz 
ery 
No. 15. After having completed the preceding series of obser- 
Segoe the Rites glass of the microscope was protected from 
the action of the hydrofluoric acid by cementing upon it a plate 
of thin prion with Canada balsam. A large number of experi- 
ments were then made with slips cut from the same piece ee 
window glass, similar to No. 1, with the object of ascertaining 
by the microscope whether the residue of the reaction was E 
talline, and whether, if so, it could have any influence wu pon the ’ 
