This test is made by weighing the specimen dry, then saturating it with water, weighing again, and stating the absorption as a percentage of the dry weight. The Commission of the Brick Manufacturers' Association oppose the use of this test, but recommend the following procedure for the test when used: I. The number of bricks for a standard test shall be 5.
II. The test must be conducted on rattled bricks. If none such are available, the whole bricks must be broken in halves before treatment.
III. Dry the bricks for 48 hours at a temperature ranging from 230 degrees to 250 degrees F. before weighing for the initial dry weight.
Soak for 48 hours, completely immersing the brick.
After soaking and before reweighing wipe the brick until free from surplus water and practically dry on the surface.
Reweigh the samples at once on scales which are sensitive to I gram.
The increase in weight due to absorption is to be calculated in percentage of the dry weight of the original bricks.
The commission also adopted the following resolu tion: " Resolved, That, in the opinion of the commission, any paving-brick which will satisfy the requirements of reasonable mechanical tests will not absorb sufficient water to prove injurious to it in service. We therefore recommend that the absorption test be abandoned as unnecessary, if not actually misleading." The purpose of this test, when made, is to insure the proper burning of the brick to a compact and non absorbent structure. It is probable, as claimed by the commission, that these qualities will always be shown by the other tests, and that this one is not of very great importance, but in many instances it may give useful information. A good paving-brick will not usually absorb more than 4 per cent or 5 per cent of water, but the amount of absorption depends largely upon the nature of the material from .which the brick
is made. ' Many of the shale bricks absorb less than I per cent of water if properly burned, while some of the so-called fire-clay bricks when of equally good quality will absorb 3 per cent or 4 per cent. A specification which would insure the proper burning of the one class would exclude the best of the other class. A limit to the amount of absorption allowable is, however, commonly set in specifications.
The requirement of drying 48 hours is probably, in most instances, sufficient and reduces the moisture in the brick so that the further loss from continued drying would be very slight, but the saturation of the brick will not usually be accomplished by immersing for 48 hours. Some bricks will in that time have taken up but a small part of the water they would finally absorb, and much longer time would be neces sary to give a complete indication in this particular. Some experiments by Mr. Harrington of St. Louis, the results of which were presented to the Brick Manufacturers' Association, showed a considerable change in the quantity of water absorbed by some bricks through a period of 24 weeks, and a consider able variation in the rate of absorption by different bricks. • The application of the test as proposed may serve to show whether the absorption is within the proper limits for a paving-brick, and when properly applied to particular makes of brick may indicate the degree of burning, although it may be of much value in the comparison of the qualities of different bricks where each shows results within reasonable limits.