or GLASS, AJH) THE EESISTANCE OF GLASS VESSELS TO COLLAPSE. 215 
White Crown-glass. 
Sand 100 parts. 
Carbonate of soda .... 38 parts. 
Lime 11 parts. 
A clear transparent glass, hard under the action of the grindstone, and highly infusible. 
The specific gra\ity of these different kinds of glass varies greatly; the following 
Table gives the result of several determinations : — 
Specific Gravity of Glass. 
Best flint-glass . . . 
3-078713 
Best flint-glass ..... 
3-0777J 
Common green glass . . 
2-527912 
Common green glass 
2-5289,1 
White crown-glass . . . 
2-449812 
White crown-glass . 
2-4510J 
Section I.— TENACITY 
OF GLASS 
^2-5284 
A few experiments were made upon the tenacity of glass, by tearing specimens asunder 
by a direct tensile strain. These results, however, owing to the following circumstances, 
are not so satisfactory as could be wished. In breaking glass by the method adopted for 
other materials, namely, by suspending weights to it, there is danger that its great rigidity 
and brittleness may occasion its fracture before the entire cohesive force 
has been balanced by the strain applied, from the vibration of laying 
on the weights. In the experiments upon globes, however, in which a 
uniform water pressure was employed, the tenacity of the glass was ascer- 
tained with more accuracy, and any failure in the present experiments 
is therefore the less to be regretted. The glass to be broken by a ten- 
sile strain was obtained of the form shown in fig. 1, drawn smaller at the 
middle to secure fracture at that part. These specimens were fixed in a 
pair of wrought-u’on shackles, and rested by their shoulders upon a thick 
india-rubber washer placed on the turned faces of the shackles. In this 
state they were suspended to a firm support, and a scale-pan attached to 
the lower shackle. Weights were then added, with the greatest care, till 
the specimen fractured. In this manner the following results were ob- 
tained ; — 
Experiment 1. 
Annealed Flint-glass. 
Least diameter .... 0-57 in. 
Least area 0’255 sq. in. 
Breaking weight, 5831bs.=2286 lbs. per square inch. 
2 G 2 
