TKST. 35 



number of blows required to desl roy t he test piece is used to represent 

 (he touo-hness. A sullieieiit number of results have not yet been 

 obtained with this test to warrant their publication. 



Tlie cylindrical test pieces employed are made with a core saw 

 designed for the purpose. It consists of a steel tube Mipported by 

 journal^ in a vertical position and held in a cast-iron frame. A link 

 motion lever rests on the upper end of the tube on a ball bearing 1 . A 

 spiral spring is attached to the free end of the lever by which the 

 downward pressure of the tube can be adjusted. Water is fed in the 

 top of the tube by a small rubber hose, and at the center is a pulley 

 wheel by which the tube is revolved at about 800 revolutions per 

 minute. The bottom or cutting end of the tube is set with bort by a 

 specially designed method. 'Phis saw cuts very rapidly and the wa-te 

 is very much less than in cube cutting, in addition to which the cylin- 

 drical test piece is better adapted for this test. 



ABSORPTION TEST. 



The method used for determining the absorptiveness of rock is not 

 intended to give the porosity but merely 7 the number of pounds of 

 water that is absorbed by a cubic foot of rock in ninety-six hours. 

 A smoothly worn stone, between 20 and 60 grams in weight, which 

 has been through the abrasion test is used. After being weighed in 

 air. it is immersed in water and immediately reweighed in water. 

 After ninety-six hours of immersion it is again weighed in water. 

 The absorptivencss of the rock is expressed by the following formula: 



Number of pounds of water absorbed by a cubic foot of rock 



in which A is equal to the weight in air. B the weight in water imme- 

 diately after immersion, C the weight in water after absorption for 

 ninety-six hours, and 62.5 the weight of a cubic foot of water. From 

 these weights the specific gravity and the weight per cubic foot of the 

 rock art' also determined. 



The method first used by (iilmore." and later by Winchell and 

 Williams, 6 differs from this method in that the stone used in the t-t 

 was taken out of the water in which it was immersed, its Surface dried 

 with a filter paper, and its weight taken every twenty-four hmirs until 

 absorption ceased. The absorptiveness was expressed by giving the 

 number of parts by weight of stone required to absorb one part by 

 weight of water. The method used in this laboratory is in no way better 

 than the earlier method except that it requires less manipulation and 

 the results are more practical for road builders. Table I. on page 13, 



"A. A.Uilmore. Report on Building Stom-s of tin- I'nite.l State-. Is7-".. ; 



*> J. F. Williams. Annual Report of the Arkansas Geological Survey, 1890, p. 47. 



