The whole problem, apart from the consideration of foundations, can be stated to be that of selecting an asphalt which has a high tensile strength at low temperatures and consequently has a {airly low fusing point and devising means of hardening this asphalt without oxidation or the sacrifice of essential characteristics and of combining the hardened" asphalt with a definitely proportioned mixture of very fine sand. This has been accomplished as' the result of exhaustive experiments and tests which have been carried out in the Departmental Road Materials Testing Laboratory for the past ight years. It is a well-known fact that the addition to asphalts Portland cement or pulverized Unie has a hardening effect on the mixture and these two substances have been used by the mana-facturers of, asphaltic paving material throughout the world. The idea generally prevails that the "Piller," by which name the ccémnént or lime used for this pur-poe is "known, enters into, come form of chemical combination with the asphalt, An electric extractor still was accordingly designed and locally manufactured, by means of which it possible to by centrifugal action and solvents the er contained in a sample of road surface. ind, asthe result of tests car: ried out by this machine, that absolutely no chemical change had taken place in the filler, its Jaction of the asphalt being purely mechanical.
Text read from the printed page and cleaned; old type leaves the occasional error.