AIO Progress in Science. (July, 
so as to prevent access of air. The oven being charged with the articles to 
be tempered, they are made to slide into the adjoining bath without being 
handled, and the contents of the bath, having no supply of external air, are 
not liable to inflame. Jn order that the shape of the tempered articles may 
not be affected, particularly flat glass, the floor of the oven is made to cant, 
so that, when the glass is heated on it, it is turned to a sloping position, and 
the glass slides into the bath, along a surface arranged in it at the same angle 
as that of the oven floor. The clearness of the glass may be affected by the 
dust of the furnace flame, which is apt to settle on the glass and chill its 
surface. This is avoided by heating the glass in a muffle, to which the flame 
has no excess, being applied externally. The shock of the fall of glass into 
the bath is prevented by fixing in it a sheet of wire gauze, or asbestos fabric, 
for the glass to fall on. Of course the condition of working would be con- 
siderably modified where glass manufacturers adopted the toughening process 
in their own works. In such case the toughening process would simply take 
the place of the present annealing process, than which it is much more speedy 
and economical. The glass would then be treated just at the point at which 
it passes from the fluid to the solid condition, and would not require re- 
heating. By the substitution of this process for that of ordinary annealing, 
the saving would be considerable. There would be, first, the saving of the 
fuel used in the annealing ovens; next, the saving of the time required for 
annealing ; thirdly, the saving in breakages, besides a saving in labour as 
well as in other directions. The physical change which glass thus treated 
undergoes is no less complete than remarkable. Its extreme brittleness is 
exchanged for a degree of toughness and elasticity, which enables delicate 
glass articles to be thrown indiscriminately about the room, and more sub- 
stantial ones to resist the impact of heavy iron weights falling from consider- 
able heights. Upon my first making the acquaintance of toughened glass 
articles at the offices of Messrs. Abel Rey and Brothers, 29, Mincing Lane— 
Messrs. Rey being the representatives of M. de la Bastie—watch-glasses, 
plates, dishes, and sheets of glass, both coloured and plain, were thrown 
across a large room, and fell spinning on the floor. Water was boiled in a 
tempered glass saucer for some time over a brisk fire, and the saucer 
was quickly removed to a comparatively cold place, and stood on iron, 
but was in no way affected by change of temperature. A small piece of 
plate-class was held in a gas flame until the corner became very hot. 
The glass proved a bad conduétor of the heat, which did not extend any 
appreciable distance beyond the point of contact with the flame, neither was 
the glass cracked from unequal expansion, nor was it damaged by sudden im- 
mersion in cold water. In order to judge of the comparative resistance 
offered by untoughened and toughened glass to the force of impact, a piece of 
the former, measuring 6 inches by 5 inches, by one-eighth inch thick, was sup- 
ported in a frame about half-an-inch from the floor. A 2-ounce brass weight 
was then dropped upon it from 12 and 18 inches respectively without damage, 
but on the height being increased to 24 inches, the glass was broken into 
several fragments. A piece of toughened glass of the same size, but rather 
thinner, was then treated in the same way, at heights increasing a foot at a 
time up to Io feet, but without producing the slightest visible impression. 
I say ‘‘ visible” impression, because it is possible that, by the repetition of the 
blows, the structure of the glass may have become imperceptibly altered. 
We all know that by repeated blows the fibrous nature of wrought-iron becomes 
exchanged for the crystalline character of cast-iron. Finding the 2-ounce 
weight to make no impression, an 8-ounce iron weight was substituted, and was 
dropped on the glass from a height of 2 feet, and then of 4 feet, without 
fracturing it. On the height being increased to 6 feet, however, the glass broke 
with a distin@ report. But here another phenomenon presented itself; instead 
of the toughened glass being broken into some twelve or fifteen large angular 
pieces, as was the ordinary glass, it was literally reduced to atoms. There 
were, it is true, some pieces about half-an-inch square, but these were traversed 
in all direGtions by delicate lines of fracture, and, on being gently touched, 
crumbled into small pieces; and many of these small pieces were easily re- 
