ANS:B - hardness test of stone

Hardness Test:

For determining the hardness of a stone, the test is carried out as follows:

i. A cylinder of diameter 25mm and height 25mm is taken out from the sample of stone.
ii. It is weighed.
iii. The sample is placed in Dorry\'s testing machine and it is subjected to a pressure of 1250 gm.
iv. Annular steel disc machine is then rotated at a speed of 28 rpm.
v. During the rotation of the disc, coarse sand of standard specification is sprinkled on the top of the disc.
vi. After 1000 revolutions, the specimen is taken out and weighed.
vii. The coefficient of hardness is found out from the following equation:

Coefficient of hardness = 20 - loss of wt. in gm/3.