and Rock Densities at High Temperatures. 



Fig. 1. 



metal by means of a graphite rod (R in fig. 2), held always in 

 contact with the bottom of the crucible by a spring at its lower 

 end. The other terminal from the cell connected, through 

 the pan on which the weights were placed, with the graphite 

 cage, which carried a pointed pin (A in fig. 1) on its upper 

 cross-bar. The circuit was complete through the galvanometer 

 when the graphite point touched the sur- 

 face of the metal. This arrangement re- 

 quired that the inverted float-crucible 

 should be insulated from the cage, and also 

 that the cage should not touch the large 

 crucible containing the metal. 



Fig. 1 is a section of the apparatus as 

 used, showing how these requirements were 

 met. G is the inverted graphite float-cruci- 

 ble, containing a block (S) of the substance 

 to be examined. F is the graphite cage or 

 frame. The platinum wire F hangs from 

 the lower cross-bar of this frame through a 

 small hole (H in fig. 2) in the bottom cover 

 of the furnace, and on its lower end is hung 

 a copper* or aluminum pan, W, for the 

 weights. The stem (B) on the upper cross- 

 bar of the cage allows cage and crucible to 

 be lifted free of the liquid metal before its 

 solidification at the end of the measure- 

 ments, by means of a hook let down from 

 above. The float-crucible is insulated from 

 the cage by the ring of magnesia (E), and 

 the whole is pinned together by two graph- 

 ite pins about a millimeter in diameter, so 

 that the float can be lifted up with the 

 cage. Magnesia was here used instead of 

 porcelain, because the latter yielded slowly 

 at high temperatures to the constant bend- fig. l. Graphite 

 ing stress exerted by the crucible stem. apparatus for deter- 



The crucible, C, containing the metal, mining the volume of 



t -, -, , ' c , i i solid and liquid sili- 



was held upon a column of tubes and screens C ates. 



of Marquardt porcelain or alundum, locked 



together so as not to get out of alignment. The lowest tube 



stood upon three set screws (D, fig. 2) by which the column 



could be adjusted vertically until the float and cage swung 



free. Similar screens above the crucible prevented loss of 



heat by radiation upward. 



The temperature was measured by a platinum platin-rhodium 

 thermo-element inclosed in a glazed Marquardt tube, which 

 was immersed in the metal close to the side of the crucible in 



