THE RATTLER TEST.
It may be of interest to recount some of the efforts which have led up to the present standing of the rattler test. During the earlier years' experience in the construction of brick pavement the judgment of those in charge of the work was the only guide used when passing upon the quality of paving brick. It was soon seen that some test to measure the ability of a brick to resist wear was needed, and the use of the foundry rattler or tumbler, employed in foundries for cleaning castings, was suggested. Brick were placed in these rattlers with a charge of foundry shot, which is generally composed of a, miscellaneous lot of broken castings of various sizes and weights and of varying degrees of roughness and irregularity. The rattler, with its charge of brick and shot, was then rotated for some time, and the loss in weight of the brick was determined. It is easy to see that there was small chance of anything like uniformity in making this test. Each individual used the rattler which was available for the purpose, without reference to its size. The speed used in the test was whatever the foundry happened to-be using. The total number of revolutions depended also upon the time the rattler was run, and this varied. The weight of the foundry shot used and the size and condition of the pieces were whatever happened to be in use in the foundry where the test was made, though this was sometimes varied by using what the individual making the tests con sidered to be better. Some engineers were somewhat more definite and specified that a given weight of miscellaneous foundry shot was to be used. In 1896, H. J. Burt* reported that specifications from fifteen cities showed the following ranges in the dimensions of the rattler and conditions of the test : Length of rattler, 24 to 54 inches ; diameter, 15 to 40 inches ; speed, revolutions per minute, 15 to 45 ; duration of test, 30 to 360 minutes; weight of iron in the charge, 50 to 800 pounds; Loss permissable in one hour, 3 to 10 per cent. These figures show some thing of the variation in practice at that time.
It is quite evident that this lack of uniformity was conducive to con fusion. The engineer was not able to compare the brick which he ac
cepted with the material which the engineer of a neighboring city re jected. The manufacturer could not tell definitely whether his product would fill the requirements in a city where he had not furnished brick. There was considerable difference of opinion on the effectiveness of the tests specified in certain cities in determining the toughness and hard ness of brick. The amount and nature of the foundry shot used in some cases rendered the test merely an abrasion test. Perhaps the greatest confusion was due to the lack of explicitness in the specifica tions. As an illustration the following example is cited. In 1895 when the writer was engage by the city of Chicago to make tests of brick from thirty yards in several states to find what makes of brick came up to the requirement of the specifications that the loss in one hour test should not exceed 12 per cent, he asked for instructions on the size of rattler, speed, and amount and nature of the foundry shot to be used in the test, and was told that these matters had not been specified and that he was to use his own judgment concerning them. Of course, in such cases manufacturers were not able to determine what grade of brick was wanted, and municipalities were uncertain about the quality of the pavement which they were putting down.
A number of efforts were made to standardize the rattler test. One of the earliest attempts was made by Prof. Ira 0. Baker, in 1890, by subjecting brick which had seen service in a pavement and pieces of natural stones cut to standard form and size to the action of a rattler in which were also placed small pieces of scrap iron. This method was unsatisfactory on account of the trouble and expense of preparing the test pieces of natural stone and the lack of uniformity in the stone, as well as because as used it did not properly combine the two actions of impact and abrasion. Later, the same investigator made a series of tests using 2-inch cubes of brick and stone with a charge of foundry "stars," but this method did not prove satisfactory.