OF GLASS, AIsT) THE EESISTAHCE OF GLASS VESSELS TO COLLAPSE. 223 
Croimi-glass Cube. 
Experiment 18. 
Area =0-82 x 0-92 incli=0-7534 square inch. 
Height =0-9 inch. 
Crushed with 16,475 lbs. = 21,867 lbs. per square inch. 
This crushed suddenly after bearing the weight some time, and was reduced almost 
to powder. 
Table IV. — Summary of the Results of Experiments on the Resistance of Cut Glass 
Cubes to Compression. 
Description of glass. 
Area of specimen, 
in square inch. 
Crushing weight, 
in lbs. 
Resistance to crushing per 
square inch. 
in lbs. 
in tons. 
Flint-glass 
0-9312 
0-9702 
0-9996 
0-9604 
13,257 
12,809 
13,257 
11,353 
14,235 
13,202 
13,262 
11,820 
6-355 
5-894 
5*921 
5-276 
Green glass 
0-9800 
1-1880 
20,059 
23,535 
20,468 
19,945 
9*116 
8-904 
Crown-glass 
0-7534 
16,475 
21,867 
9-762 
Hence the mean resistance to crushing of cubes of glass is equivalent to a weight of 
lbs. 
For flint-glass 13,130 
For green glass 20,206 
For crown-glass 21,867 
Mean .... 18,401 
Comparing these with the preceding results on glass cylinders, we have the mean resist- 
ance of the former experiments to the mean resistance of the above as 30,153: 18,401, 
or as 1‘6 : 1. 
General Observations relative to the Besults of the Experiments on the Resistance of Glass 
Cylinders and Cubes to Crushing. 
With iron and some other materials, when a short column undergoes a pressure in 
the direction of its length, rupture takes place in a plane having a determinate angle to 
the axis of the column, this plane being the section of least resistance. Neglecting the 
friction of the surfaces. Coulomb found this angle to be 45° ; and allowing on an average 
10° for the limiting angle of friction, the angle of the plane of rupture may be taken 
at 55°. To fulfil this condition, the length of the column to be crushed should be at least 
three times its radius : when the length greatly exceeds this limit, the rupture will be 
effected by the tendency of the column to bend ; and when the length is within this limit, 
2 H 2 
