6 BULLETIN 246, U. S. DEPAETMENT OF AGKICULTUBE. 
uniformly over the entire top surface of the test specimen, and may be 
much greater if the area over which the load is applied is less than 
that of the top surface. Since paving brick in use are seldom required 
to withstand a pressure of more than about 2,000 pounds per square 
inch, and since inferior brick may possess relatively very high resist- 
ance to crushing, a knowledge of the crushing strength is clearly of 
little value in comparing the relative excellence of different makes of 
brick. It is, therefore, usually considered unnecessary to specify a 
definite requirement as to the crushing strength of paving brick. 
TESTING THE BRICK. 
Definite methods of testing paving brick have been in general use 
for only a comparatively few years and have only recently under- 
gone a pronounced change. The object of all tests is to determine 
whether or not a given quality of brick is suitable for use in con- 
structing pavements and to furnish a basis for comparing different 
classes of brick. The methods have, therefore, been repeatedly 
changed, not only in order to make the results obtained indicate more 
definitely the quality of the brick, but also with a view to establish- 
ing uniformity, so that results obtained in different laboratories may 
be intelligently compared. A discussion of the most important tests 
follows in more or less detail. 
FIELD TEST. 
The general appearance of a paving brick is, to an experienced eye, 
a valuable indication of its quality and will frequently suggest the 
advisability of applying routine tests to some particular part of a 
shipment. Unfortunately the knowledge gained from experience 
with one kind of brick can not be safely relied upon in inspect- 
ing other brick made by a different process or from a different 
class of raw material. A further limitation to this method of testing 
lies in the fact that the results obtained do not admit of numerical 
evaluation, and can not, therefore, be very accurately described. 
This test is nevertheless valuable, and since no apparatus other than 
a hand hammer is needed, it can always be employed. 
The test consists simply in making a careful inspection of the 
brick individually and collectively. The size is tested by making 
measurements, the shape by arranging a number of brick in the order 
in which they are intended to be placed, and the quality by an exami- 
nation of both the exterior and interior of a number of samples. 
TRANSVERSE TEST. 
The transverse strength of a brick is determined by supporting it 
upon two knife edges and applying a load on the opposite side and 
