108 NEW YORK STATE MUSEUM 



ered steel die of circular section, about i y^ in. diameter, mixed with 

 water, and subjected to a pressure of 2,300 kilograms (about 3 tons). 

 The resulting briquette is then put aside for at least one week, so that it 

 may thoroughly dry. 



It was at first thought that a test by direct compression would deter- 

 mine the cementing power of the stone. A number of briquettes were 

 tried in this way, but the results were not very satisfactory. On further 

 consideration, it appears that a test by impact would more thoroughly 

 determine the cementing power of the stone then that by compression, 

 and this method would have the further advantage of approximating 

 more closely to the actual conditions obtaining on roads; accordingly a 

 machine was devised for testing the briquettes by impact. With this 

 machine a hammer one kilogram (2 2-3 lbs) in weight can be dropped 

 freely from any desired height upon a plunger under which the briquette 

 to be tested is placed. The hammer works automatically and is tripped 

 at the desired height. Attached to the plunger is a lever, pivoted atone 

 sixth of its length from the plunger, and carrying a pencil at its free end. 

 The pencil has a vertical movement five times as great as that of the 

 plunger, and its movement is registered on a drum against which the 

 pencil presses. The drum rotates through a small angle at each stroke 

 of the hammer. An automatic diagram is thus taken of the behavior 

 of the briquette throughout the whole test. 



An analysis of the diagram so taken shows at once the number of blows 

 required to cause the destruction of the briquette. A very interesting 

 point is brought out by these diagrams, viz, in every case the diagram 

 shows that the plunger rebounded at each stroke until the briquette began 

 to fail. This behavior is exactly analogous to the elastic phenomena ob- 

 served in all material of construction; consequently the point at which 

 the briquette ceases to rebound corresponds to the elastic limit of the 

 material. Beyond this point the briquette falls to pieces rapidly. 



Briquettes were made from many kinds of stone, and were tested in 

 this machine. It was thought desirable to use a constant blow for all 

 the briquettes, and a short experience indicated a fall of 1 ^ in. as suitable, 

 since it broke the most tenacious materials with a moderate number of 

 blows, and yet was not too great to permit the careful determination of 

 the properties of the poorer stones. All the briquettes were 1 in. 

 high. 



The surface of a macadamized road is constantly being abraded and 

 recemented. Evidently a road made from a material which has the 

 property of recementing in a high degree will keep in better condition 

 than one made from a material of lower recementing power. It was 

 therefore desirable to determine the recementing properties of the stones 

 tested. A new set of briquettes was made, differing from the former 

 only in that they were of constant weight instead of constant height. 

 These were tested in the manner described above, and then were remade 

 and retested. 



It has not been thought desirable to present herewith the complete data 

 obtained from the impact test: as the series is not yet completed. The 

 writer has, however, collected and shown in the accompanying table 

 some ot the more important results thus far obtained, a sufficient number 

 to indicate the scope of the work done. In this table the stones are 

 arranged in the order of their power of resisting abrasion. Column 1 



