OF GLASS, AND THE EESISTANCE OF GLASS VESSELS TO COLLAPSE. 217 
annealed. There is also a considerable discrepancy between the strength of green and 
crown-glass when in the form of bars and when in the form of globes. In the case of 
the bars, the results are as I’O to 1T3 in favour of green glass, whilst in the case of the 
globes, the results are as 1*0 to 1-2 in favour of the crown-glass. These discrepancies 
may, however, be accounted for from the different condition of the material in relation 
to annealing in the two cases, or from an imperfect bedding of the specimen, causing 
a distortion of the strain out of the direction of the axis of the specimen, or from 
accidental vibration in laying on the weights. 
Sectiok II.— EESISTANCE OF GLASS TO CEHSHING. 
The next series of experiments was instituted with a view of determining the powers 
Fig. 2. 
Fig. 3. 
of resistance of glass to a direct crushing 
force. The specimens subjected to experi- 
ment were small cylinders (fig. 2) varying in 
length from 1 to 2 inches, and about three- 
quarters of an inch in diameter. They were 
placed for the purpose of crushing within 
the box a (fig. 3), thin packings of soft lead 
being interposed between the glass and the 
parallel crushing surfaces of the box and 
its solid steel piston h ; in this way a firm and 
uniform bearing surface was secured, and 
the crushing force was applied perpendi- 
cularly in the direction of the axis of the 
specimen. Fig. 3 exhibits the general 
arrangement of the crushing apparatus, con- 
sisting of a lever A, 8 feet long, supported 
on a strong cast-iron base B, B. The crush- 
ing force obtained by placing weights in the 
scale-pan hung at the extremity of the lever 
is transmitted through the piston J, to the 
specimen to be crushed, c. 
. Q ins 1 • 
