or GLASS, AND THE EESISTANCE OE GLASS VESSELS TO COLLAPSE. 221 
Taking the means of the above values, and reducing the weights to tons, we have — 
Table III. — Mean Compressive Resistance of Glass. 
Description of glass. 
Height 
of cylinder, 
in inches. 
Crushing weight per 
square inch, 
\ Mean crushing weight 
per square inch, 
in lbs. 
in tons. 
in lbs. 
in tons. 
r 
1-0 
29,168 
13-021 
Flint-glass < 
1-6 
20,775 
9-274 
‘ >27,582 
12-313 
1 
2-0 
32,803 
14-644 
;j 
r 
1-0 
22,583 
10-081 
1 
Green glass < 
1-5 
35,029 
15-628 
^31,876 
14-227 
1 
2-0 
38,015 
16-971 
J 
Crown-glass | 
1-0 
1-5 
23,181 
38,825 
10-348 
17*332 
j 31,003 
13-840 
The mean resistance of glass to a crushing force is therefore, from the above experi- 
ments, equivalent to 13-460 tons per square inch. Assuming the above numbers to 
represent the comparative values of each kind of glass, and taking flint-glass as the 
standard, we have their respective strengths as follow : — 
Green glass . . . 1152 
Crown-glass . . . 1124 
Flint-glass . . . . 1000 
The specimens were crushed almost to powder from the violence of the concussion^ 
when they gave way; it however appeared that the fractures occurred in vertical 
planes, sphtting up the specimen in all directions. This characteristic mode of disin- 
tegration has been noticed before, especially with vitrifled brick and indurated lime- 
stone. The experiments following on cubes of glass which were exposed to view during 
the crushing process, illustrated this subject further: cracks were noticed to form some 
time before the specimen finally gave way; then these rapidly increased in number, 
splitting the glass into innumerable irregular prisms of the same height as the cube ; 
finally these bent or broke, and the pressure, no longer bedded on a firm surface, 
destroyed the specimen. The annexed ideal sketch (fig. 5) may give some 
notion of the fractures of a cube, supposing all the particles were restored 
to their position after crushing. 
The specimens employed in the following experiments were cut from the 
square heads of the pieces of glass employed in the experiments on tensile 
strain (fig. 1). These pieces were approximately cubical; and their size prevented their 
insertion in the box a (fig. 3) ; they were therefore crushed between parallel steel discs, 
exposed to view. The crushing was more gradual, and was not effected so completely 
in these experiments as in those on small cylinders, the fragments being in every case 
larger after the conclusion of the experiment : it must further be recollected, in com- 
paring these with the preceding experiments, that the cylinders were cut off, of the 
required length, from rods of glass drawn out when molten to the diameter desired, so 
MDCCCLIX. 2 H 
