290 Joty—On the Volume Change of Rocks and Minerals attending Fusion. 
objectionable when the substances to be subsequently dealt with are non- 
conductors. This fact was ascertained in the following manner:—A bead of 
potassium carbonate (K,CO;) was prepared, having closely the dimensions of the 
platinum beads. The melting point of this substance, as determined by Carnelley, 
is 834°C. The test was made as to whether the melting point, as determined from 
the curve, would afford this number. It was first ascertained that the appearance 
of melting was perfectly characteristic and readily recognisable. From liquid to 
Sana 
: 
| 
[= we 
bes 
ometric Curve. 
zl Expansion of Platinum 
| 
700 800 900 1000 1100 1200 1300 
z 
> 
Temperature Rise 
—400 500 600 
0 1 12 13 14 15 16 17 18 19 20 21 R22 23 R4 25 
Galvanometer 
Fig. 6. 
solid the change is, perhaps, most conspicuous. The phenomena will be described 
later. The following observations were made :— 
Galv. 
16:0 Not melting. 
17:0 55 
17:6 Melted. 
17°3. Not melted. 
17°5 Slowly melting and freezing. 
The temperature corresponding to 17:5 ascertained from the curves (fig. 5) 
is closely 900° C. These curves give the rise of temperature above that of the air. 
But the melting-point instead of being some 915° C. should be 834° C. There is 
thus an error of excess in the readings obtained from the platinum thermometer 
of 7 or 8 per cent. at this temperature. What is this due to? The most likely 
explanation is that the rise in temperature in the case of the platinum is partly 
effected by conductivity through the suspending wire, which very nearly touches 
the jaws of the slit in the top of the oven, and partly by conductivity from the 
