results obtained by the latter method give the following mean 

 results : 



Tenacity per square inch 

 in pounds. 



Flint-glass 2413 



Green glass 2896 



Crown-glass 2346 



Resistance of Glass to Crushing. The experiments in this section 

 were made upon small cylinders and cubes of glass crushed between 

 parallel steel surfaces by means of a lever. The cylinders were cut 

 of the required length from rods drawn to the required diameter, 

 when molten, and then annealed, in this way retaining the exterior 

 and first cooled skin of glass. The cubes were cut from much 

 larger portions, and were in consequence probably in a less perfect 

 condition as regards annealing. Hence, as might have been antici- 

 pated, the results upon the two classes of specimens, although con- 

 sistent in each case, differ widely from one another. 



The mean compressive resistance of the cylinders, varying in 

 height from 1 to 2 inches, and about 0'75 inch in diameter, is given 

 in the following Table : 



The specimens were crushed almost to powder by the violence of 

 the concussion ; it appeared, however, that the fracture occurred in 

 vertical planes, splitting up the specimen in all directions. Cracks 

 were noticed to form some time before the specimen finally gave 

 way ; then these rapidly increased in number, splitting the glass 

 into innumerable prisms, which finally bent or broke, and the 

 specimen was destroyed. 



