190 GEOLOGY OP OHIO. 



however, lies wholly in the way in which it is carried out. The best 

 brick ever made can be reduced to a powder in an hour or two and the 

 poorest bricks can be made to come out of the test unscathed, if the 

 operator so desires. 



The process when carried out honestly and to the best advantage is 

 as follows : A rattler, such as is used for cleaning castings in a foundry 

 is procured. It should be thirty-six inches in diameter and forty-two to 

 forty-eight inches long. It should be supported from the ends without 

 the use of a continuous shaft and its cross section should be an octagon. 

 This machine should be equipped to run by power and be started and 

 stopped quickly at the will of the operator. The speed of revolution 

 should not exceed twenty-six or be less than twenty-two times per minute 

 to secure the maximum grinding effect of the charge. 



The bricks to be tested should first be weighed accurately and marked 

 with white lead paint in several places each. It is also a useful precau- 

 tion to break off a small chip of each brick and number it so as to use it 

 as a guide, if all marks are worn off from the samples. The bricks are 

 then thrown into the rattler, which should not be more than a third filled. 

 A rattler of the dimensions given will only handle about forty bricks at a 

 time. For every three bricks, a billet of wood about eighteen inches 

 long by two and a half inches square should be thrown into the rattler 

 and the lid bolted tight. The machine should be started and run for 

 1,000, l,500or 2,000 revolutions according to the severity of the test 

 desired. The bricks are now weighed again individually and collectively 

 and the percentage loss of each sample determined. 



In conducting a rattler test on these lines, the friction and blows 

 given and received are wholly by the bricks themselves. The billets of 

 wood prevent the too great violence oi the falls and blows and the gen- 

 eral result is that of frictional wear of brick on brick, in which the fittest 

 survives. 



If the amount of brick be increased the efficiency rapidly diminishes 

 as the space left for falling and jostling is diminished. In the same way 

 if the bricks do not fill the rattler third full, so also the violence of the 

 test increases. 



The utility of putting the bricks into a rattler half full of angular 

 scrap iron is very much doubted — it is undoubtedly a comparative test, 

 but the conditions in this case find no parallel in the actual conditions of 

 wear. We have no interest in testing bricks for their fitness to do work 

 which they will never be called on to do. Rather, the conditions of street 

 wear should be duplicated in the application of force as nearly as is possi- 

 ble in this form of test. 



Under such a test as has been described brick will lose from five per 

 cent to thirty-five per cent in an hours run. 



Another method of testing the abrasive strength of bricks is the grind- 

 ing table. A horizontal iron disc of six or eight feet in diameteris covered 

 with the brick to be tested and each brick is weighed down with forty or 



