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oleaginous compound. It is covered from the external air by 
a lid, and within it is a basket of fine wire gauze, m, hung from 
brackets. A tube, n, contains a thermometer, o, to indicate 
the temperature ; and by this tube the contents of the bath may 
be added to, or any excess may overflow by the discharge-pipe, 
p. A plug, q , on the cover may be removed to observe the in- 
terior, without entirely uncovering the bath. A fire-truck, r, 
charged with live fuel, heats the bath to the desired temperature. 
The glass is introduced into the preparatory oven by an opening, 
s, in the outer wall, and thence it is moved through the open- 
ing, e , on to the floor of the oven, a. The workman who watches 
the glass through the spy-hole, t , when he finds it at the proper 
heat, pushes it by an iron rod to the slope, c, whence it slides 
into the bath and is received on the basket, m. When the 
glass has cooled to the temperature of the bath, the lid is re- 
moved, and the basket, m, is raised out of the bath with the 
tempered glass. 
In tempering sheet glass the arrangements of both oven and 
bath are slightly modified. In place of the sloping exit for 
articles from the oven to the bath, M. de la Bastie has a rocking 
table, which is hinged underneath to the mouth of the oven, 
and which also forms the floor of the oven. When the glass has 
been sufficiently heated, the workman, by means of a lever, tilts 
the table, and the glass slides gently down an easy incline on 
to a table set at a corresponding incline in the bath. If it is 
not of importance that the transparency of the glass should bu 
preserved, no special precautions are taken to prevent the dust 
from the furnace settling on its face. Where, however, clear- 
ness is required, the glass is heated in a muffle, perfect trans- 
parencybeing obtained. The process of tempering or toughening, 
exclusive of the time required for heating the glass, occupies 
but a minute or so, the glass being immersed in the bath and 
at once withdrawn and set aside to cool. The cost per article, 
as may be supposed, is merely nominal. 
Gflass which has been treated in this manner undergoes a 
physical transformation as complete as it is remarkable. Its 
appearance is in no way altered, either as regards transparency 
or colour — if coloured glass be so treated — and its ring or sound 
is not in any way affected. It has, however, exchanged its 
distinguishing characteristic of extreme brittleness for a degree 
of toughness and elasticity which enables it to bear the impact 
of heavy falling weights and smart blows without the least in- 
jury. A great number of experiments have been made, the 
results of which fully corroborate this fact. From these it will 
suffice to select a few by way of illustration. Watch-glasses, 
which perfectly retain their transparency, have resisted every 
attempt to break them by crushing between the fingers, or by 
