BAKUS.1 
CALIBRATION OF ELECTRICAL PYROMETERS. 
87 
time, otherwise the ebullition, which is regular in the case of pure 
metal, becomes irregular and bumping when it holds perceptible quan- 
tities of oxide in solution, or when such adhere to The glass. Solids 
may be either melted and poured into the tube from above, or they may 
/R\ 
Fig. 10. Perfected form of boiling-tub 
Scab 
Fig. 10a. Boiling-point tube 
for annealing long wires. 
Scale, ,V 
be introduced as powders and then cautiously melted. In case of or- 
ganic solids heat must be applied very gradually to prevent charring 
or gumming, until the whole mass is liquefied. Usually the substance 
may be left to cool and solidify in the tube without incurring liability 
to breakage, a special tube being set apart for each boiliug-point sub- 
stance. 
(741) 
