CLASSIFICATION OF J)ATA. 45 



have excellent binding power, some varieties being suitable for the 

 heaviest macadam traffic. Linn-stones vary givjitly hut generally 

 hind well; they are soft and frequent ly improve under trallic. (^uartx- 

 ites are almost always very hard, brittle, an<l have very low binding 

 power. The slates are usually soft, hrittle, and lack binding power. 



When samples of rock are received at the laboratory without a 

 request f Of Specific information, the method of procedure is as foll< >\s -: 

 The samples are subjected to the tests already enumerated, and the 

 results are classified and compared with those of like value and known 

 worth in practice. These results, together with a statement of the 

 particular group of traffic to which the materials are best suited are 

 forwarded to the sender". When samples are sent for the purpose of 

 ascertaining which is best suited for a particular mid, the sender is 

 requested if possible to supply the laboratory with a census of the 

 traffic or, if this is impracticable, to state what class of traffic pa - 

 over the road. The tests are then made and the results classified and 

 compared as in the previous case. Full information regarding the 

 climatic conditions is obtained from the Weather Bureau and that 

 material is selected which the results indicate to be best suited to the 

 conditions. Allowance is always made for at least a 15 per cent 

 increase in the volume of traffic due to the improved conditions, if the 

 road is to be macadamized for the first time. 



As time goes on and the behavior of these tested materials is studied 

 and records of traffic are accumulated the value of the laboratory tests 

 will constantly increase. Cooperation among the increasing number 

 of laboratories in the country is much needed and uniform methods of 

 testing should be adopted. The American Society for Testing Mate- 

 rials has been asked to appoint a committee to investigate the whole 

 subject of the testing of road materials with a view to bringing t he- 

 work of the various and widely separated laboratories under standard 

 conditions. As soon as the rapidly growing mass of data on this 

 subject is thus made uniform and comparable it will be of the very 

 highest value. 



Those who are familiar with the problems of rural road building 

 know the great difficulty of selecting among the available materials 

 for a particular road the one which will give the best results for the 

 least cost of construction and maintenance. There are, undoubtedly, 

 practical road builders whose judgment on the road-making quality of 

 a rock is excellent, but experience with materials of construction in 

 general has proved that it is wise and economical to test the physical 

 properties of materials before entering on the expenditure of large 

 sums of money. Bridge building would not have become the high art 

 that it has had not the careful and systematic testing of materials put 



See forms on page 75 of the Appendix. 



