ing laboratories and the yards of the more progressive brickmakers. As the rattler test is now conducted, the loss in weight, after being rattled an hour, varies greatly according to the inherent toughness of the clay, according to the care given in its manufacture, according to the degree to which it is vitrified and finally according to its shape. When different clays are treated exactly alike, so as to exclusively bring out the individual toughness, the rattler loss is found to range from 5 to 40 per cent and usually between 12 to 20 per cent in brick that have proved to wear well in practice. The most important and least evident factor in the toughness of a paver is the individuality of the clay itself and which can only be determined by the rattler test or else by use in the pavement. Shales and clays that look to be similar and even have a more or less comparable chemical composition are found to vary greatly in toughness when made into pavers under identical conditions and with equal care. So great is this difference and it is so difficult to predict this factor that no shale or clay should be considered for pavers until this extremely important information has been obtained from a large, working test. The care taken in manufacture to grind sufficiently fine, to thoroughly screen out all large particles, to pug to a uniform and proper consistency, to so run the brick machine as to secure a bar of uniform, unbroken, non-ragged structure, to repress properly, to handle the wet brick without strain or injury, to dry equally and uniformly, and to finally so fire the kiln as to bring it slowly but progressively to a complete vitrifying heat and to then gradually cool it without air-checking, overburning or rolling the brick, all have great influence on the toughness of a paver. The variations shown in testing different brick from the same kiln demonstrate how important the manufacturing factors are and how difficult it is to completely control them. The shape of a brick or block will materially affect the rattler loss according as it is an unrepressed, square cornered paver or whether the sharp edges and angles have been removed by repressing, as the former will quickly chip off in the first fifteen minutes in the rattler test. It has also been found that the ratio of depth to width affects the rattler loss, as the narrower the brick the greater the loss, but as a uniform size has been quite generally adopted, this is not usually an important factor. To attempt to define a standard for the toughness or rattler loss is unwise and dangerous, as local conditions as to traffic and financial considerations are liable to modify any arbitrary standard. The heavy traffic on the down-town streets in the large cities calls for the toughest brick obtainable, whereas the much less severe travel on the residence streets and alleys in the same city will enable a local brick that is cheaper to make a good record, even though it may not be quite as tough as a distant brick made from a better clay. Many small cities and towns are able to secure the great advantages of a brick pavement by using local pavers that could not stand the expense of shipping in distant brick, even though of a better quality. For the freight is such a heavy charge on long shipments, on account of their great weight (or about 4 tons per 1,000), that it might render the cost more or less prohibitory. The toughest brick will unquestionably always make the best record when laid on the street and prove the most economical in the end at almost any price, but in most cases the tax payers and the paving contractors want the cheapest brick obtainable and the toughness or wearing value is too frequently made a secondary consideration, even when the community can afford the best brick in the market. The rattler test is an excellent medium for comparing paving brick with granite and, while the latter is usually very much tougher than the average paver, some brick have made as good a test as good granite in the same rattler. Granite is found to vary as much as 600 per cent in the rattler loss, which is partly due to the difference in the granites and partly due to weathering or incipient decay. For granites decay and change into clay on prolonged exposure to the weather, and while this requires a period of time that runs into the hundreds of years, the outcrops or exposed parts of a granite quarry are liable to be considerably softer and less resistant than the material from greater depths. Brick men are apt to credit granite with being a uniformly hard and very tough rock, whereas, there are liable to be marked variations in its paving value. Tests made in Boston* on eighteen different paving brick, in which granite blocks were added to the rattler charge, five of the brick showed a smaller loss than the granite. Another series of tests made at Cornell University** on seventeen different makes of paving brick with trap blocks as a standard for comparison and rated as 1.00, one shale paver showed a loss of only 0.87 and a thoroughly vitrified fire clay brick a loss of only 1.66; the loss of the other brick ranged up to 17.18 and averaged 8.3. As trap is a tougher rock than granite, this is a most encouraging exhibit and augurs well for the future of high grade pavers when engineers insist on the very best quality obtainable and are willing to pay for the enhanced value. For manufacturers can produce a much better brick than the trade is usually willing to pay for. An addition of $3 to $5 per 1,000 to the present costs will permit of so much more care being taken through *Engineering News, June 2, 1892. **Engineering News, April 18, 1895. out the entire manufacturing process, and especially in the burning and annealing, as to result in a so much superior article as to make this additional investment a measure of true economy. For a brick that still presents a smooth, true pavement at the end of twenty to thirty years is very much cheaper at an advance of $10 per 1,000 over an inferior brick that is so cobbled and worn at the end of ten years that it has to be heavily patched if not renewed. When square-cornered brick are tested with those with rounded corners, the former show a much greater loss, as the sharp angles break off readily. This, however, is just what happens in practice, and is a fair comparison as regards brick to brick, but is unfair as a test of the clays, as they should have similar corners to give a reliable comparison. METHOD OF TESTING PAVING BRICK. EYE EXAMINATION.-There is no more rapid method of arriving at the merits of a paving brick than by the trained, experienced eye when assisted by the free use of a hand hammer. A critical examination by the eye and hand hammer when combined with proper experience and good judgment, can usually reliably pass on the merits of a brick in a few minutes, while the laboratory tests take hours. But our vocabulary is too limited to make the nice distinctions that are possible to the trained eye and it is difficult to arrive at a satisfactory numerical evaluation. As in most expert work, it is a personal decision that is founded on good judgment, training and experience; and while it leaves little to be desired when backed by integrity for the numerous and rapid decisions of municipal engineering, it is testimony that can be besmirched and impugned when attacked by unprincipled self-interests. As definite standards must be adopted that admit of general use and comparison, and as specific figures Influence of the Necessity of Inspection Should be at the Kiln are required that will permit the drawing of specifications and living up to same, a series of tests have been devised which admit of general application and enable definite standards to be attained and lived up to. The necessity of such figures is so well recognized that there are not only numerous testing laboratories scattered all over the country, but the engineering departments of most cities have laboratories that are well equipped to test brick and to furnish specific information when differences of opinion arise between the contractor and inspector about the quality of brick. Usually the inspection of the brick is carried on at the work in the street, when about to be laid, and the condemned brick are a serious expense to the contractor, who is often an innocent sufferer; they have a curious way of disappearing around the corner and reappearing laid in the street. The proper place to inthey are also a menace to the vigilance of the inspector, as they have a curious way of disappearing around the corner and reappearing laid in the street. The proper place to inspect the brick is at the kiln as they are being loaded out, where it can be much more rapidly, easily and safely performed and where there is no such strong incentive to smuggle condemned brick into the work. For even if the paving is done under a maintenance bond, the contractor is usually willing to take risks as to the durability of questionable brick that the cautious engineer would not entertain. LABORATORY TESTS.-The tests that are made to determine the complete merits of a paving brick are: |