Table No. 7 gives the composition of limestone from different localities.

In five samples of Missouri limestone the calcium carbonate averaged 99.2%.

Limestones tested by General Gillmore for crushing strength

varied from 3450 to 25,000 lbs. per square inch.

CHAPTER III.

ASPHALT.

ASPHALT or bitumen under some name has been in use for many ages. The terms have been used so much synonymously as well as interchangeably that it is often difficult to tell just what varieties are referred to. The practice is still kept up to a certain extent, some authorities speaking of asphalt, others of asphaltum, and some of both, while all are practically referring to the same substance. Some specifications have mentioned pure asphaltum. It would be extremely difficult at the present time to establish legally what pure asphaltum is. As one writer has said, asphalt is an occurrence and not a distinct substance.

In America natural bituminous pavements are called asphalt; in France, asphalte comprimé; in Germany, Stampf-Asphaltum; and in England, asphalte.

In the English translation of the Bible it is stated that Noah was told to pitch the ark with pitch; and in another chapter in Genesis, that when the tower of Babel was built slime was used for mortar; and in Exodus, that the ark of bulrushes in which Moses was found was daubed with slime and pitch. In each of these cases the Latin version renders the words " slime and "pitch as "bitumen" except in the case of Moses' ark, both words being used in the same sentence; "pitch" is rendered pice, the ablative form of pix.

In the Greek version these words are all rendered aopaλros, or from the same root except as above in Exodus, where ao paλtonioon is used. This latter word is said by Liddell and Scott to be the same as 10σaopaλros,which means a compound of asphalt and pitch. Riddell and White define bitumen as 'A kind of asphaltum, Jew's pitch, or fossil tar," and add that it was

frequently found in Palestine and Babylon. Bitumen, they say, is from the Hebrew word chemar, and aopaλtos from two Hebrew words meaning "mud."

ἄσφαλτος

Liddell and Scott also say that the belief that aopaλros is derived from opallo is erroneous.

It is also stated in profane history that bitumen was used in building the hanging gardens of Babylon, and in other works of masonry construction in both Babylon and Nineveh. It was also used in making cisterns water-tight. Tradition says that this pitch came from the springs of Oyen Hit on the Euphrates.

In the light of all this it is safe to say that some forms of bitumen have been known to, and used by, the human race from very early periods. In some sections of Europe examples of masonry constructed with a bituminous cement are still extant.

Before proceeding to an extended discussion of bitumen in any of its forms, it will be fitting to examine the various definitions that have been given to it by different writers and students.

Whatever form is studied, it must be understood that bitumen is the essential base of all, and that will be considered first. Prof. S. F. Peckham, formerly of the University of Michigan, and who has been engaged more or less in the study of this subject since 1865, defines bitumen as "That large class of substances occurring in nature as minerals and consisting chiefly of mixtures of compounds of carbon and hydrogen, with nitrogen, sulphur, and oxygen as more rare constituents."

Prof. Sadtler says: "The word bitumen in mineralogy is applied to hydrocarbon mixtures of mineral occurrence, whether solid, liquid, or gaseous."

Clifford Richardson, formerly Inspector of Asphalt and Cements, says: "The natural bitumen which is known as asphalt is composed, as far as we have been able to learn, of unsaturated hydrocarbons and their sulphur derivatives with a small amount of nitrogenous constituents."

Mr. A. W. Dow, at present Inspector of Asphalt and Cements, Washington, defines bitumen as "Any and all hydrocarbons, whether natural or artificial, soluble in carbon bisulphide."

Leon Malo, an eminent French writer on the subject, says that in 1861 he made the following definition, and in 1897 he can do no

better than to reiterate it: "Bitumen or pitch, the materials which impregnate asphalt."

As defined by Dana, "Asphaltum or mineral pitch is a mixture of different hydrocarbons, part of which are oxygenated."

Richardson: "Asphalt may therefore be defined as any hard bitumen, composed of unsaturated hydrocarbons and their derivatives, which melts upon the application of heat to a viscous liquid." Mr. Dow defines both asphaltum and asphalt:

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Asphaltum-A natural bitumen, all or a portion of which is soluble in petroleum naphtha, and in most cases found associated with various mineral and organic substances."

"Asphalt-Any and all natural deposits containing asphaltum." An unknown writer: "Asphalt is a compact bitumen, a product of the decomposition of vegetable matter, consisting mainly of hydrocarbons with variable quantities of oxygen and nitrogen."

Leon Malo: "Asphalt, calcareous rock impregnated naturally by bitumen or pitch."

Prof. Peckham: "The words natural gas, naphtha, petroleum, maltha, asphaltum, and asphalt are not names of things, but words. which indicate accidents of occurrence to which any species of bitumen may be subject. When a true system of classification of the species and subspecies under bitumen has been reached, it will be found that a species may occur in nature in any or all of the several conditions from natural gas to asphalt. A true system, therefore, must name and classify the bitumens themselves."

These different definitions from these different investigators have been given in order that it may be clearly seen in what respect the people who are studying the questions to-day, and who are probably as conversant with the subjects as any one in the world, differ, and in what they agree.

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The great difference between the definitions of Leon Malo and the American writers will be noticed. According to him, nothing but what is known in this country as rock asphalt can be considered under that name. As a matter of fact, all asphalt pavements laid in the American manner are called artificial pavements in Europe. That is, the paving material must be formed by nature in order to constitute a real asphalt pavement.

The American definitions are very much alike in essential

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points, except that Mr. Dow uses and defines "asphaltum" and asphalt." There does not seem to be any necessity for considering an intermediate substance between bitumen and asphalt. Neither does there seem to be any reason why some writers should use "asphaltum" and others "asphalt" when referring to exactly the same substance. Asphalt, being the shorter and the more nearly English in form, will be adopted for use in this work.

A careful study of the foregoing definitions would suggest a combination of some of them by which the ideas of the writers might be incorporated together, with a result that might be more satisfactory than any one alone.

Prof. Peckham's definition of bitumen is scientific and exact, but it is long and inconvenient. It does not seem necessary in a definition to give all the constituents of a substance nor all its properties, but sufficient only to render it easily recognized. It would seem, therefore, that by transposing Prof. Sadtler's words and adding some of Mr. Richardson's, a definition of bitumen might be reached that would not be too long and would satisfy all scientific requirements.

This is suggested, then: "Bitumen-Any unsaturated hydrocarbon mixture of mineral occurrence, whether solid, liquid, or gaseous."

In connection with the above may be quoted a statement of Prof. Peckham's: "Bitumens from natural gas to asphaltum include compounds and mixtures of compounds belonging to all the known series of hydrocarbons."

He also divides bitumens into the following: solid, asphaltum; semi-fluid, maltha; fluid, petroleum; volatile, naphtha; gaseous, natural gas.

In speaking further of maltha he says: "Some of these fluid varieties of bitumen both in Europe and America pass by insensible degrees and by natural causes into maltha, which is a semi-fluid viscous form of bitumen, known as mineral tar and just as clearly to be distinguished in consistence from petroleum as common tar is to be distinguished from olive-oil. I have found the change by which California petroleum is converted into maltha to be due to two causes, viz., evaporation and indirect oxidation. When air, ozone, or chlorine is passed through the paraffine petroleums, they