302 Joty—On the Volume Change of Rocks and Minerals attending Fusion. 
curve is reproduced in figure 9. Its general resemblance to that determined by 
the expansion of platinum will be recognised. 
Taking this curve into use, the following observations on augite were made. 
This specimen of augite was in the form of crystals having the prism angle of 
87°, and black in colour. The former augite dealt with was fragmentary and 
more transparent. 
The present specimen was prepared by radiation in the platinum tube. Its 
diameter was 0:06 inch. 
Galy. Micrometer. Toa Ty Temperature, Uae iat 
hh Centigrade. ee 
10°85 31 0:0018 340° 0:0054 
14°3 74 0:0043 520 0:0129 
15°9 98 0:0057 615 0:0171 
Oe: 194 0:0110 810 0:0350 
On raising the temperature to 1320°, a bubble blew out and put an end to the 
experiments. The noteworthy difference between this curve and that formerly 
found for augite is probably to be referred, principally, to the presence of 
minute vesicles in the present specimen. ‘The presence of bubbles will tend to 
render the curve of expansion steeper, and the accident which put a stop to these 
experiments appears to confirm this idea. 
The natural expansion so found is, however, not without its teaching, with 
reference to lavas fused under low pressure. 
This curve is given on Plate XVIIL., and is marked Augite IT. 
ORTHOCLASE, 
The series of experiments was closed with an observation on orthoclase (Plate 
XVIII.). The bead was prepared in the oxyhydrogen flame. It was soon 
rendered quite clear and was visibly free from vesicles. 
The diameter of the bead was 0-056 inch. 
Galv. Micrometer. moe Tee eae 
12-0 26 0-0016 390° 0:0048 
16:3 50 0:0031 640 0:00938 
19-9 68 00048 860 . 0°0129 
23-4 94 0-0059 1090 00177 
25°8 130 0-0081 1240 00243 
27-1 150 0-0094 1320 00282 
27°8 140 00088 1350? 00264 
28°7 210 0-9132 1400 ? 0:03596 
