HOLMAN, LAWRENCE, BARR. — MELTING POINTS. 



223 



For the melting metals, after trial of several devices, the one 

 shown in Figure 5 (of exactly half size) was settled upon as proving 

 very satisfactory. The crucible G (usually of fire clay) is supported 

 by clay blocks in the double-walled fire-clay furnace, F. A carbon 

 block, E, channelled to fit the crucible, forms its cover, and a carbon 

 diaphragm D inside the crucible serves to support some powdered 

 carbon shown by the dotted mass. The object of these carbon parts 

 was to prevent oxidation of molten metals, and they proved very 

 eflfective in the case of aluminum, silver, and copper. G G was an 



Fig. 5. 



asbestos diaphragm supporting a non-conducting layer of fibrous 

 asbestos, A, A. The temperature was controlled by the blast lamp B. 

 The clay crucible was one inch in diameter outside, and the amount of 

 metal employed ranged from 11 grams (gold) to 35 grams (copper). 

 Larger amounts might be advantageous, but with 30 to 35 grams 

 it was easily possible to obtain a constant indication for five minutes 

 during the melting or solidifying of copper. No difficulty whatever 

 was experienced with this arrangement with silver, gold, or copper. 

 With aluminum, however, a peculiar action occurred, the cause of 

 which in the time available for investigation could not be determined 



