188 Mr. Carl Barus on the Fusion 



These data are given in the chart (fig. 10), temperatures in 

 degrees C, as abscissae, volume-changes as ordinat.es. A 

 chart of the same character may also be constructed from 

 Table II., but this is superfluous. In figure 10 the actual 

 expansion of the rock is shown by the heavy line dcbef, and 

 the numbers attached to the points of observation indicate 

 the times at which they were made. The apparent expansion 

 of the rock is shown by the light line Ikgh, where the ordi- 

 nates of the solid contour are nearly zero. Finally the ex- 

 pansion of the fusion-tube is represented by the dotted line 

 deai. The amount of break at a, which is even smaller in 

 Series III., indicates the amount of draff or a shortening- of 



7 CO 



the length of the platinum tube by the solidifying rock 

 within, and furnishes an estimate for the trustworthiness of 

 the solid results. It is interesting to note that in both 

 Series III. and IV. the first length measurements of the tube 

 are smaller than the second at the same temperature, showing 

 that the tube has to some extent recuperated from the strain, 

 or that the amount of end thrust has diminished. It is 

 similarly possible to note the sag as expressed by the cold 

 lengths (25*49 centim. in Series II., 25'47 centim. in Series 

 III., and 25*45 centim. in Series IV.) of the platinum fusion- 

 tube. Finally, the depth of the liquid meniscus at the outset 

 of Series III. and IV., and at about the same temperature, 

 was A,=*50 centim. and \ = '62 centim., showing enlargement 

 of the bulk of the tube. These changes, which are in part 

 allowed for, show that viscosity introduces no serious dis- 

 crepancy. Regarding the differences of X and A f / the 

 remarks made in § 14 apply. 



An inspection of the curve dbef as a whole indicates 

 the occurrence of sharply marked solidification at 1093°. 

 This is sufficient evidence to prove that rock-fusion (diabase) 

 is thoroughly normal in type. A method is thus given in 

 which the solidify ing-point is determined free from non- 

 intrinsic tests. 



Finally, the contraction on solidification, 3*9 per cent, in 

 Series III., and 3*4 per cent, in Series IV., is established, 

 for diabase at least, beyond question. It is to be noted, more- 

 over, that the smaller value (IV.) corresponds to a larger 

 drag during solidification on the platinum tube (ef. Tables II. 

 and III.). Hence the value 39 per cent, is the more 

 probable. In general, temperatures (0 1? 2 , 3 ) are nearly 

 alike so long as the glass is liquid. This ceases to be the case 

 alter solidification ; and since the top of the fusion-tube is 

 apt to be colder than the bottom, some of the solid contraction 

 expresses itself in dilatational strain, § 14. 



