6S6 Prof. J. Joly on the Closure of Small 



subject of careful experiment; and the densities of these 

 materials were determined by accurate measurements of the 

 dimensions and weight of the cubes. The cubes were cut 

 by Krantz, special precautions being taken to secure the 

 parallelism of two special faces intended to take the pressure 

 of the hydraulic press. 



The volume of the granite cube was 5*07 3 cm. = 130*299, 

 and its weight 338*744 gram, giving a density =2*600. 

 A pressure of 20 tons was applied for 20 minutes with no 

 apparent effect. The pressure was then raised to 30 tons 

 and applied for 70 minutes without visible effect. Baised 

 now to 35 tons one corner split off, but the cube remained 

 otherwise sound. Next day at 36 tons it exploded violently. 

 This is 9 tons or 20,160 lb. per square inch. 



This appears to be a fairly high result. The strongest 

 mica granite cited in Merrill's tables * gave 23,358 lb. per 

 square inch, and of 59 such granites cited only 7 exceed 

 20,000 lb. per square inch. These tests were mostly made 

 on 2 in. cubes as in the present case. 



The volume of the basalt cube was 5*05 3 cm. = 128,775 c.c. 

 Its weight was 374*194 grams. Eence density = 2871. 

 20 tons applied for 18 minutes produced no effect. At 

 27 tons a small crack near one side appeared, and a piece 

 flatted out at 37 tons. Next day the pressure was applied 

 anew and slowly increased to 59 tons, when there was a 

 violent explosion and the cube was scattered. 



This is 14*75 tons, or 33,000 lb. per square inch, and 

 compares favourably with certain similar rocks, diabase, 

 cited by Merrill, Joe. cit., the strength of which in no case 

 reached 27,000 lb. per square inch. 



In the case of the lithograpltic limestone the cube volume 

 was the same as in the case of the basalt, and the weight 

 343*950 grams: giving a density of 2*639. 



liaising the pressure at intervals approximating to 10 

 minutes from 20 tons, as much as 50 tons was reached by 

 increment of 10 tons, when a small chip broke away at one 

 corner. At 53 and 54 tons the cube began to chip rapidly — 

 finally cracking vertically through the middle. 



This is 13*5 tons = 30,240 lb. per square inch. Adams 

 applied similar tests to this rock, his results ranging from 

 28,000 to 40,000 lb. per square inchf. 



The obsidian was not tested for crushing strength. Its 

 specific gravity, determined by weighing one of the hemi- 

 spheres in water, was found to be 2*380. 



* ' Stones for Building- and Decoration/ New York, 1897. 

 t Frank 1). Adams and L. V. King, The Journal of Geology, vol. xx, 

 1912. 



