BARUS.l 
CALIBRATION OF ELECTRICAL PYROMETERS. 
91 
troduce no more than is just necessary to cover the central tube <l<l. 
The lower crucible is surrounded by a furnace, FF FF, made of the 
same non-conducting mixture which is used in Fletcher's small injector 
furnace. Heat is communicated by means of the injector blow-pipe A 
B (7, gas entering at the tube C, air at E. Both G and E are provided 
with stopcocks. The products of combustion escape at D. The cru- 
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Fig. 13. Original form of boiling crucible. Scale, J. 
cible a acta has been fitted into the bottom of F F, through which the 
central tube dd projects. All cracks and crevices are closed up with 
carded asbestos. In this way the space below the furnace remains 
practically cold and the thermo-element may be inserted or withdrawn 
with great convenience. A few screens protect the cold junction from 
radiation altogether. 
Perfected forms of boiling-point crucible. — This double crucible appara- 
tus behaves excellently until the extreme white heats are reached, after 
which the porcelain and the cement become viscous, and leakage and 
failure of the experiment is the invariable result. Moreover, the influx 
(745) 
