N. B. M. A. Standard. In February, 1901, the National Brick Manufacturers' Association modified its previous standard (§ 742) by adopting Talbot's form of abrasive material, and pub lished the following specifications for the standard method of conducting the rattler test of paving brick, which have been widely adopted.
1. Dimensions of the Machine. The standard machine shall be 28 inches in diameter and 20 inches in length, measured inside the rattling chamber. Other machines may be used, varying in diameter between 26 and 30 inches, and in length from 18 to 24 inches; but if this is done, a record of it must be attached to the official report. Long rattlers must be cut up into sections of suitable length by the insertion of an iron diaphragm at the proper point.
2. Construction of the Machine. The barrel may be driven by trunnions at one or both ends, or by rollers underneath, but in no case shall a shaft pass through the rattler chamber. The cross section of the barrel shall be a regular polygon having fourteen sides. The heads shall be composed of gray cast iron, not chilled nor case-hardened. The staves shall preferably be composed of steel plates, as cast iron pears and ulti mately breaks under the wearing action on the inside. There shall be a space of one fourth of an inch between the staves for the escape of the dust and small pieces of waste. Other machines may be used having from twelve to sixteen staves, with openings from one eighth to three eighths of an inch between staves, but if this is done a record of it must be attached to the official report of the test.
3. Composition of the Charge. All tests must be executed on charges containing but one make of paving material at a time. The charge shall be composed of the bricks to be tested and iron abrasive material. The brick charge shall consist of that number of whole bricks or blocks whose combined volume most nearly amounts to 1,000 cubic inches, or 8 per cent of the cubic contents of the rattling chamber. (Nine, ten, or
eleven are the number required for the ordinary sizes on the market.) The abrasive charge shall consist of 300 pounds of shot made of ordinary machinery cast-iron. This shot shall be of two sizes, as described below, and the shot charge shall be composed of one fourth (75 pounds) of the larger size and three fourths (225 pounds) of the smaller size.
4. Size of the Shot. The larger size shall weigh about 7i pounds and be about 2} inches square and 41 inches long, having edges rounded to a radius of about I inch. The smaller size shall be inch cubes, weighing about seven eighths of a pound each, with square corners and edges. The individual shot shall be replaced by new ones when they have lost one tenth of their original weight.* 5. Revolutions of the Charge. The number of revolutions of the stand ard test shall be 1,800, and the speed of rotation shall not fall below 28 nor exceed 30 per minute. The belt power shall be sufficient to rotate the rattler at the same speed whether charged or empty.
6. Conditoin of the Charge. The bricks composing a charge shall be thoroughly dried before making the tegt.t 7. Calculating the Results. The loss shall be calculated' in percent ages of the weight of the dry brick composing the charge, and no result shall be considered as official unless it is the average of two distinct and complete tests, made on separate charges of brick.* Fig. 125 shows a common form of the standard rattler. The chamber on each side of the partition is of the standard form, consequently two lots of brick may be tested at the same time. Fig. 126 shows a form of rattler, designed at Purdue University, which permits easy access to the rattling chamber without the trouble of removing a stave. The rattler is enclosed in a dust-proof case made of sheet iron and having felt-packed joints. A door in the lower part of the case provides for the removal of a pan which receives the dust and chins from the rattler.