Inorganic Matter. This indicates in some cases the nature of the dense bitumen.

Insoluble Organic Matter.-This affords an indication of whether oil has been distilled destructively.

Bitumen Insoluble in 88°B. Naphtha.-The hydrocarbons insoluble in paraffin naphtha are termed "asphaltenes" and those which are soluble "malthenes." The former tend to give body and consistency and the latter contribute adhesive properties to a road material. Blown oils contain very high amounts of insoluble hydrocarbons, sometimes as much as 25 to 30 per cent. The character of the bitumen dissolved in naphtha, after the solvent has evaporated, is instructive, for a sticky residue indicates better road building qualities in the original material than that which is greasy.

Soluble Bitumen Removed by H2SO, and Saturated Hydrocarbons in Total Bitumen.-These tests are mainly of value as indicating the source of the material under examination. Clifford Richardson gives the following explanation of the significance of the tests in The Modern Asphalt Pavement:

Hydrocarbons in general are divided into those which are saturated and those which are unsaturated, the former being stable and the latter reactive and very susceptible to change, combining with or being converted into other hydrocarbons by the action of sulphuric acid and other reagents. The saturated can be separated from the unsaturated hydrocarbons by strong sulphuric acid, and this will be found to be a very important means of differentiating the oils and the solid bitumens among themselves, by determining the relative proportions of these two classes of hydrocarbons which they contain.

Solid Paraffin. This test confirms the information obtained from an inspection of the residue after the test of the loss at 160°C. The heavy liquid hydrocarbons of the paraffin series are probably more detrimental in road oils than are the solid paraffins. Fixed Carbon.-Fixed carbon is the coke resulting from the ignition of the bitumen in the absence of oxygen.

Fluxes

Fluxes are petroleum products which are mixed with harder bituminous materials to soften them to any desired consistency. Petroleum with a paraffin base furnished the first flux used in the asphalt paving industry.

Asphaltic or semi-asphaltic flux is the residuum left on distilling petroleum having an asphaltic or semi-asphaltic base to a point where the residuum is a dense liquid when cool but any further distillation will produce a solid residuum when cold. It is characterized by a relatively low amount of saturated hydrocarbons. While it resembles natural maltha in some respects, it differs in remaining soft after heating to 400°F., most malthas becoming hard pitches after such treatment..

ASPHALT AND NATIVE SOLID BITUMENS1

The following definition of "asphalt" has been adopted by the American Society for Testing Materials:

Solid or semi-solid native bitumens, solid or semi-solid' bitumens obtained by refining petroleum, or solid or semi-solid bitumens which are combinations of the bitumens mentioned with petroleums or derivatives thereof, which melt upon the application of heat and which consist of a mixture of hydrocarbons and their derivatives of complex structure, largely cyclic and bridge compounds.

This definition is dependent upon the same society's definition of "bitumens," which is:

Mixtures of native or pyrogenous hydrocarbons and their non-metallic derivatives, which may be gases, liquids, viscous liquids, or solids, and which are soluble in carbon disulphide.

These definitions were prepared after numerous conferences of road engineers and producers of materials, and while adopted by the society are not accepted by all specialists.

The following definitions are given by Clifford Richardson in The Modern Asphalt Pavement:

Native bitumens consist of a mixture of native hydrocarbons and their derivatives, which may be gaseous, liquid, a viscous liquid or solid, but, if solid, melting more or less readily on the application of heat, and soluble in turpentine, chloroform, bisulphide of carbon, similar solvents, and in the malthas or heavy asphaltic oils. Natural gas, petroleum, maltha, asphalt, grahamite, gilsonite, ozocerite, etc., are bitumens. Coal, lignite, wurtzelite, albertite, so-called indurated asphalts, are not bitumens, because they are not soluble to any extent in the usual solvents for bitumen, nor do they melt at comparatively low temperatures nor dissolve in heavy asphaltic oils. These substances, however, on destructive distillation

1 Revised by Prévost Hubbard, chief of road materials tests and research, United States Office of Public Roads.

Solid bituminous materials are those having a penetration at 25°C. (77°F.) under a load of 100 grams applied for five seconds, of not more than 10. The significance of "penetration" is explained on page 121.

Semi-solid bituminous materials are those having a penetration at 25°C. (77° F.) under a load of 100 grams applied for five seconds, of more than 10 and a penetration under a load of 50 grams applied for 1 second of not more than 350.

Liquid bituminous materials are those having a penetration at 25°C. (77° F).) under a load of 50 grams applied for one second or more than 350,

give rise to products which are similar to natural bitumens, and they have been on this account defined by T. Sterry Hunt as "pyro-bitumens,' which differentiates them very plainly from the true bitumens."

Asphalt is a term used industrially to cover all the solid native bitumens used in the paving industry and specifically to include only such as melt on the application of heat, at about the temperature of boiling water, are equally soluble in carbon bisulphide and carbon tetrachloride and to a large extent in 88° naphtha, those hydrocarbons soluble in naphtha consisting to a very considerable degree of saturated hydrocarbons, yielding about 15 per cent of fixed carbon and containing a high percentage of sulphur. Under this definition it can be seen that grahamite is not an asphalt, since it is not largely soluble in naphtha and yields a very high percentage of fixed carbon on ignition. It is also less soluble in carbon tetrachloride than in carbon bisulphide. Gilsonite is not an asphalt, since the saturated hydrocarbons contained in the naphtha solution are very small in amount and quite different in character from those found in asphalt.

Roadbuilders use the term "natural asphalts" to designate the native solid or semi-solid asphalts, and "oil asphalts" to designate the corresponding materials prepared from petroleum or maltha. Some producers of oil asphalts object to the term on the ground that the material obtained by distilling away the lighter parts of asphaltic petroleum is as "natural" as that obtained by refining native asphalts. By "rock asphalt" is meant sandstone and limestone impregnated with asphalt or maltha. 'Asphaltic sands" are mixtures of asphalt or maltha and sand, the latter in loose grains which fall apart when the bitumen is extracted; many of them are called rock asphalts because in their natural condition the maltha cements them into a rock-like mass.

The sources of the asphalts used in the United States are given in the accompanying table. The quantities of materials there stated were not all used for road and street purposes, as there are many other uses to which some of them are put.

Trinidad Asphalt.-Trinidad asphalt comes from the island of that name. The main source is on La Brea Point, about 28 miles from Port of Spain, the chief town. Here there is a circular pitch lake of nearly 115 acres extent, between which and the sea are other pitch deposits more or less mixed with sand. The former furnishes the "lake asphalt" and the latter the "land asphalt" of the paving industry.

The material in the lake is described by Clifford Richardson as an emulsion of water, gas, bitumen, fine sand and clay. It is in constant motion owing to the evolution of gas, and for this reason, whenever a hole is dug in the surface, whether deep or shallow, it rapidly fills up and the surface resumes its original level after a short time. Although soft it can be readily flaked out with picks in large conchoidal masses weighing 50 to 75

pounds. It is honey-combed with gas cavities and resembles a Swiss cheese in structure. It is of uniform composition, as follows: Water and gas volatilized at 100°C., 29 per cent; bitumen soluble in cold carbon disulphide, 39 per cent; bitumen absorbed

American Production and Importation of Asphaltic Materials, 1915 (Compiled from report by John D. Northrop in Mineral Resources of the United States, 1915. Output stated in tons of 2000 pounds, except in case of imports, which are in tons of 2240 pounds)

*Refined in the United States from imported Mexican petroleum. †There are discrepancies in the figures in the report.

by mineral matter, 0.3 per cent; mineral matter, 27.2 per cent; water of hydration in clay and silicates, 4.3 per cent.

Trinidad land asphalt reached the places where it is found either by overflowing from the lake or by intrusion into the soil from the same subterranean source that supplies the lake asphalt.