22 OC. M, Wetherill on the Crystalline Nature of Glass. 
3. A pure transparent English glass (a salt cellar), various 
vessels of French and Bohemian ware, very thick glass stoppers, 
glass of various colors, such as white bluish or green, and differ- 
ently tinted glass fluxes and plates, all yielded similar crystals. 
4. Some of the dilute residue of the reaction of sulphuric 
acid upon fluor spar having been left in a beaker glass, etched 
the same, with beautiful tufts of fibrous crystals, giving the ap- 
pearance of some specimens of agate, » 
Leydolt infers from his experiments that all glass consists. of 
an amorphous mass containing a variable proportion of erystals, 
and consequently; that not only density and composition, but 
also the more or’less uniform distribution of the crystals, and 
their nature have a marked influence upon the character and op- 
tical behavior of the glass, 
He deems the following questions to be of importance, 
1. Upon what circumstances depends the formation of the 
crystals in relation to quantit 
2. What influence have the crystals upon optic phenomena? 
3. May not their presence have an influence upon the doubly 
refracting character which glass acquires by heating and sudden 
cooling; or by pressure 
4. What substances may be dissolved in melted glass and sep- 
arated therefrom by slow cooling 
Daubrée (C. R., xlv, 792) obtained various crystals by expos- 
ing glass for weeks to the action of water and steam in seal 
iron vessels, at a temperature of 400° C. The glass was con- 
verted into a white, swollen, kaolin-like substance, composed al- 
most entirely of crystalline particles. He found many crystals 
of quartz, and also acicular forms of nearly the same composi- 
tion as Wollastonite (53 p.c. silica, 46 lime; with traces of mag- 
nesia). The quantity of water equalled half the weight of the 
glass, and the action of the water was. the same as that of the 
steam. 
Daubrée does not believe that the crystals preéxisted in the 
lass; but were formed by the action of the water. Although 
this is probable, it may be questioned whether some of the crys- 
tals were not ready formed in the glass. 
_ My own-experiments were performed by dropping strong 
liquid hydrofluoric acid upon plates of glass, using one or suc- 
cessive drops, according to the degree of etching desired. By 
this means the energy of the acid is expended upon one particu- 
dar spot of the glass, and by taking more or less of the solvent, — 
‘er by employing it of greater or less strength, the reaction is 
completely under control. 4s 4 
_ The acid was generated in the usual manner in aleaden retort _ 
wee a sou lensing he of sis same metal, cooled with a mix- — 
re ; and ice; the liquid acid was received in a plati 
crucible, also a api sa Ree: erm Sguemr gee e 
