230 
POPULAR SCIENCE REVIEW. 
ever being made upon it. The 8-oz. weight was then thrown 
violently upon it several times, but without damaging it. Its- 
destruction, however, was finally accomplished by means of a 
hammer. Perhaps the most crucial test to which toughened 
glass could be put would be to let it fall on iron. This has been 
done, and in public too. A thin glass plate was dropped from a 
height of 4 feet on to an iron grating, from which it rebounded 
about 1 foot, sustaining no injury whatever. 
As singular as any other feature presented by toughened glass 
are the results of its destruction. Ordinary glass, upon being: 
fractured, gives long needle-shaped and angular fragments. Not 
so toughened glass, which is instantaneously resolved into mere- 
atoms. The whole mass is at once disintegrated into innumer- 
able pieces, ranging in size from a pin’s point to an eighth of an 
inch in diameter. It sometimes occurs that pieces measuring 
half an inch or an inch across may remain whole, but thes& 
pieces are traversed in all directions by a network of fine lines- 
of fracture, and with the fingers are easily reduced to fragments. 
Microscopical examination shows the fragments of toughened 
glass — large and small — to follow the same law as regards the 
form and character of the crystals, and on some of the larger 
crystals being broken up they have been found to separate into 
smaller ones of the same character. The edges of these frag- 
ments, too, are more or less smooth instead of being jagged and 
serrated as are those of fragments of ordinary glass. Hence a 
diminished tendency in the former to cause incised flesh wounds 
when handled. 
When glass has been imperfectly treated, as has sometimes 
happened in M. de la Bastie’s experiments, it will not stand the- 
same amount of rough usage as will perfectly toughened speci- 
mens. The fact of the toughening process having been incom- 
plete is made manifest upon the destruction of a sample in three 
different ways chiefly. Independently of its yielding at an early 
stage either to blows or pressure, it will show upon destruction 
either needle fractures approaching in appearance those of ordi- 
nary glass, or pieces varying from the size of a sixpence to that 
of a half-crown will remain unbroken and untraversed by lines, 
of fracture. Again, the mass may be wholly fractured, but on 
looking at the fragments edgewise a narrow milky streak will ba 
apparent midway between the upper and under sides o£ the 
glass, indicating that the influence of the bath has not extended 
through the glass. Where the process has been perfe^ly applied,, 
no such phenomena are exhibited, the crystals being of uniform 
transparency throughout the whole mass. 
Such, then, is De la Bastie’s toughened glass, which possesses 
enormous cohesive power, and offers great resistance to the- 
force of impact. There is, however, one peculiarity which, for 
