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THE POPULAR SCIENCE MONTHLY. 



observe the interior, without entirely uncovering the bath. A fire- 

 truck, 2^1 chai'ged with live fuel, heats the bath to the desired tempera- 

 ture. The glass is introduced into the preparatory oven by an open- 

 ing in the outer wall, and thence it is moved through a second open- 

 in on to the floor of the oven, a. The workman who watches the 

 glass through a spy-hole, when he finds it at the proper heat, pushes it 

 by an iron rod to the slope, c7, Avhence it slides into the bath and is re- 

 ceived on the basket, k. When the glass has cooled to the tempera- 

 ture of the bath, the lid is removed, and the basket, A", is raised out of 

 the bath with the tempered glass. 



In tempering sheet-glass the arrangements of both oven and bath 

 are slightly modified, as shown in Fig. 3. In place of the sloping exit 



Fig. 3. 



for articles from the oven to the bath, M. de la Bastie has a rocking 

 table, E, which is hinged underneath to the mouth of the oven, and 

 which also forms the floor of the oven. "When the glass has been suf- 

 ficiently 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 corre- 

 sponding incline in the bath. If it is not of importance that the trans- 

 parency of the glass should be preserved, no special precautions are 

 taken to prevent the dust from the furnace settling on its face. 

 Where, however, clearness is required, the glass is heated in a mufile, 

 perfect transparency being obtained. The process of tempering or 

 tougliening, exclusive of the time required for heating the glass, occu- 

 pies 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 once withdrawn and set aside to cool.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. 



Glass which has been treated in this manner undergoes a physical 

 transformation as complete as it is remarkable. Its appeal anee is in 

 no way altered, either as regards transparency or color if colored 

 glass be so treated and its ring or sound is not in any way aft'ected. 



