and Rock Densities at High Temperatures. 23 



large. The volume increase of the two granites between 0° 

 and 575° is 5 - 07 and 5 - 82 per cent, respectively, giving a mean 

 of 5 - 45 per cent. The corresponding increase for pure quartz 

 is 5*17 per cent. 



The most probable cause of this abnormally large expansion 

 is the action of the pure quartz crystals in pushing the other 

 mineral fragments apart, increasing the apparent volume of 

 the rock. Evidence for this explanation is seen in the curve 

 giving the data of a second heating of the Alaska granite. In 

 this series the volumes are all larger, although the curve is 

 parallel to the first. The final kilogram-volume of this rock 

 after the two heatings to 600° was 393 - 7, a permanent increase 

 of 2"20 per cent. 



In the Stone Mt. granite, which was heated to 935°, a very 

 considerable permanent expansion occurred. This is probably 

 due largely to the unequal expansion of the different minerals, 

 which causes them to push each other apart, fracturing the 

 rock and rendering it porous and friable. The relative dimen- 

 sions of the block, after heating, remained the same, but it had 

 increased in volume by 9*3 per cent. 



The heating above 575° caused also the evolution of con- 

 siderable gas between the temperatures 750° and 900°. During 

 a part of the time the gas was evolved quite regularly, causing 

 the floating system to rise and fall rhythmically, this rise and 

 fall being caused by gas accumulating, lifting the float crucible, 

 and escaping through the graphite top. Chamberlin found in 

 the Stone Mt. granite 076 of its volume of gas, consisting 

 chiefly of hydrogen. Water, which he did not determine, 

 would add considerably to this, just as in the case of quartz 

 already discussed (see p. 21). The escape of these gases 

 probably contributes to the shattering and permanent dila- 

 tation. 



This permanent dilatation in granite and other rocks has 

 frequently been noted by other observers, and is indeed to be 

 expected in any heterogeneous material. Any change of 

 temperature will cause the constituent parts to expand 

 unequally in accordance with their differing dilatation coeffi- 

 cients, and if the temperature range is large enough so that 

 the stresses thus set up exceed the breaking strength of the 

 parts, there will be internal fracturing and opening of irregular 

 cavities. 



1ST. E. Wheeler* has determined the linear expansion of 

 several rocks used by Adams and Coker in their high pressure 

 studies. In all cases a considerable permanent expansion was 

 produced by the first heating. We have calculated from his 

 data the volumes of the Westerly (Rhode Island) granite 

 * Trans. Eoyal Soc, Canada, iv, III, 19-44, 1910. 



