ROAD OILS ARE PASSED BY LABORATORY TESTS

NOVEMBER, 1931 ARIZONA HIGHWAYS

murder, in which he was cleared by a jury. There was held the famous Bisbee deportation trial which lasted for weeks, there was the famous trial of several noted Mexicans charged with being in this country for the purpose of hatching revolutions in Mexico and for which they served a term in the federal prison -at the present it is the home of many Chinese who are here as guests of Uncle Sam and at this writing it appears Uncle Sam is tiring of playing the role of "mine host."

This charming old style of architecture, with all its beauty, will probably become a county museum in connection with the annual Helldorado celebration. That seems the destiny of this famous old building at this time.

Road Oils Used In State Highways Are Passed By Tests In Laboratory

By J. W. POWERS Engineer of Materials Diverging from concrete making materials and the apparatus and equipment necessary to test them, let us go back to the road surface again.

The present era in highway building in Arizona might be called the "dustless" era. The public demand is the criterion by which the policy of the department is formed. First it was improved location and alignment, then a high cementation, natural surfacing to give a faster, smoother road, and now the oil surface.

As building of a permanent type is too costly, to serve the purpose it was necessary to go to a more inexpensive type, thus the surface treatment with road oil was resorted to. The necessary characteristics of a good material have been gone into several times in previous articles, so this article will deal only with the oil.

The two determinations which have the most significance are asphalt content and viscosity. Upon the asphalt content of an oil depends its ability to bind satisfactorily the surfacing into a semirigid surface. All oils used by this department at the presnt time are liquid at ordinary temperatures, and have an asphalt content of not less than 65 per cent, determined by an open evaporation at 535 degrees Fahrenheit. The oil is placed in an evaporting pan and heated for the necessary time to drive off the lighter fractions and convert it into a semi-solid state. The consistency of the semi-solid is measured with a penetrometer at 77 degrees F. The penetrometer is a uniformly loaded needle which is used to penetrate, for a specific time interval, the asphalt obtained from the evaporation. Depth of penetration is read directly and is the depth in tenths of millimeters of the penetration of the needle.

Based on Penetration

For uniformity and as a standard, the asphalt content is based on an asphalt of 80 penetration. In our work on these oils we run two portions of a sample and evaporate so that we have asphalt contents which will give a penetration on each side of the standard set, and then by interpolation, we determine the exact percentage. Roughly-for each change on one per cent in asphalt content there will be a change of 20 in penetration.

As all oil treatment is done by the road mix method, it is necessary to have a measure of workability. The measure of workability is viscosity. Viscosity is measured with the Saybolt Furol Viscosimeter at 122 degrees F. The length of time in seconds it takes 60 cc to flow through a small orifice is its viscosity. The usual range of viscosity for the type of oil used is between 200 and 300 seconds.

THE OLD, OLD STORY

A backwood mountaineer one day found a mirror which a tourist had lost. "Well, if it ain't my old dad," he said, looking at it. "I never knowed he had his pitcher took."

He was so pleased he took the mirror home, stole into the attic and hid it. But his actions did not escape his suspicious wife. That night, after he was asleep, she slipped to the attic and found it. "H-m-m," she said, looking into the mirror, "so that's the old hag he's been chasin."