=Vertical Fiber Brick.=--These brick are designed to be laid with one wire-cut face up and spacing is provided by two or more beads on the side of the brick. Sometimes the vertical fiber brick has no spacing lug, it being contended that the irregularities of the brick are such as to provide all of the space required. In practice this does not always work out, as the brick are so regular in shape that when laid there is too little space between the brick to permit the introduction of a suitable filler. The use of brick without spacing lugs is just beginning and is not yet a generally accepted practice. =Wire-cut-lug Brick.=--This is a type of non-repressed brick which has spacing lugs provided by cutting one face in a special manner which provided lugs for spacing. In this type the wire cut face is the one between the brick as they are laid in the pavement. =Tests for Quality.=--The standard test for quality of paving brick is the rattler test. The brick rattler consists of a barrel of 14 sides 24 inches long, mounted so as to rotate at a speed between 29.5 and 30.5 revolutions per minute. The duration of a test is 1800 revolutions. Ten brick constitute a charge and these are placed in the rattler along with 300 lbs. of cast iron spheres. The spheres are of two sizes, the smaller being 1-7/8 inch in diameter when new, and the larger 3-3/4 inches in diameter when new. Ten of the larger spheres are used and the balance of the charge is made up of the small size. When tested in the standard manner the loss allowable for the several classes of service are as follows: ------------+---------------+---------------- | | Maximum Loss Traffic | Average Loss | for any Brick ------------+---------------+---------------- Heavy | 20 per cent | 24 per cent Medium | 22 per cent | 26 per cent Light | 25 per cent | 28 per cent ------------+---------------+---------------- =Other Tests.=--Sometimes the absorption test is specified for paving brick, but it is rarely a vitrified brick that will pass the rattler tests which fails to pass a reasonable absorption test. Absorption of water in an amount exceeding 4 per cent indicates incomplete vitrification and failure of such brick is almost certain during the rattler tests. The cross breaking test is also sometimes employed, but generally only to check the general quality of the brick. Failure in service more frequently occurs from excessive wear than from any other cause and the cross breaking test has little significance, except for brick less than 3 inches thick, which are to be laid on a sand bedding course.