640 Proceedings of the Royal Society of Edinburgh. [Sess. 
in A that a week or more can elapse before the temperature in the furnace 
falls 50° C. The action of the apparatus may also be reversed, for by 
allowing the water in A to slowly pass the tap D the gas supply will be 
gradually increased. An additional thermo-regulator may be used, if 
necessary, to prevent the initial temperature exceeding 500° C. 
Working at the Blowpipe. 
The usual operations of glass-blowing apply in this case. The low 
fusion point will at first seem to be a drawback, but with practice bulbs of 
a few inches in diameter may be easily produced. The glass remains plastic 
over a wide range of temperature. In order to weld a bulb upon ordinary 
glass, however, two or sometimes three intermediate glasses are required, so 
as to graduate the stress produced by unequal contraction. These may be 
made up as follows : — 
A. Enameller’s copper flux. 
B. 2 parts of copper flux plus * 5 part of conducting glass. 
C. 2 parts of copper flux plus 1 part of conducting glass. 
In order to blow a conducting bulb upon the end of ordinary glass a piece 
of A is melted into the end of the tube, blown to a small sphere, and burst 
at a point exactly in the axis of the tube. The thin irregular glass having 
been removed with a file, a piece of glass B is made use of in the same 
manner. Having in this way built up three small bulbs upon the end of 
the tube, the conducting glass is melted on and blown to the required size. " 
During the whole operation care must be taken to prevent the work cooling, 
and directly it is completed the whole must be annealed for at least half 
an hour. 
