CHAPTER III.

PHYSICAL AND PHYSIOLOGICAL PROPERTIES OF PETROLEUM.

PETROLEUM is oily, thinly- to thickly-fluid, seldom waterclear (rock oil, naphtha) or yellow, mostly brown to black, and, according to its color, more or less transparent.

Mineral tar or maltha is viscous, gummy, black or brownblack, and can be drawn into threads.

Both have an unctuous feel and a fatty lustre.

Density. While mineral tar has a density of 0.9 to 1.0, that of petroleum varies between 0.73 and 0.97 (from Terra di Lavore). As a rule light-colored oils are specifically lighter than dark oils.

B. Redwood has made a series of determinations of densities, which he gives in his pamphlet' in chronological order. By grouping, however, the figures of his table according to the density, the connection between the latter and the color will be immediately recognized, though the samples are derived from the remotest regions. The following table shows that, generally speaking, the density is less the lighter the oil is.

1 Cantor Lectures on Petroleum and its Products, 1886.

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In the different petroleum regions the density varies as follows:

0.779 (Klenczany). 0.902 (Harklowa).

West Galicia, 0.762 (Klenczany). 0.910 (Harklowa).

0.750 (Ropianka).

The density of petroleum sometimes varies considerably in

in the same region within narrow limits. Thus Dr. Kraemer mentions that at Oelheim (Hanover) two borings of nearly the same depth and at a distance of only 65 feet from each other yielded petroleum of 0.88 and 0.905. One and the same bed nearly always gives in the neighborhood of the outcrop an inferior oil of greater density than deeper down. In Pennsylvania, where there are three oil beds, one below the other, the oil also becomes specifically lighter with an increasing depth. Thus:

Ist oil sand (upper) 0.8750 to 0.8484.

2d oil sand (middle) 0.8235.

3d oil sand (lower) 0.800 to 0.7777.

The vertical distance from the first to the third oil sand is about 250 feet.

As a rule the specifically lighter oils furnish a greater yield of illuminating oil, though exceptions have been known. Thus Nawratil's investigations of Galician oils proved that the quantity of illuminating oil (distillate of from 302° to 572° F.) is greatest (50.4 per cent.) with a density of 0.83, and decreases with specifically heavier as well as specifically lighter crude oils; with a density of 0.90 it amounts to 28 or 29 per cent., and with a density of 0.78 to 34 per cent. However from this decrease no constant relation between density and yield of illuminating oil can be recognized.

The density of petroleum also does not furnish a sure clue to its content of paraffin, though, as a rule, the latter increases with the density.

In the practice the density of petroleum is generally determined by means of the aerometer, and indicated by degrees Baumé (B.).

The following table of equivalence may be acceptable to the reader :

Table of the Specific Gravity corresponding to each degree of Baumé's hydrometer, also the number of Pounds contained in one United States Gallon at bo° F.

One United States gallon of pure water-231 cubic inches, contains 58,318 grains (or 3779.031 grammes)=8.331 pounds avoirdupois.

One imperial gallon of pure water-277.276 cubic inches, contains 70,000 grains (or 4536.029 grammes)=10 pounds avoirdupois.

One cubic foot of pure water at 60° F. contains 1,000 ounces 62.5 pounds avoirdupois.

To reduce imperial gallons to United States gallons, divide by 1.2.

To reduce United States gallons to imperial gallons, multiply by 1.2.

To reduce United States gallons to cubic feet, divide by 7.5.

To reduce cubic feet to United States gallons, multiply by 7.5. To find the number of pounds avoirdupois in one cubic foot of any substance, multiply its specific gravity by 62.5.

To find the degree Baumé corresponding to any specific gravity:

Since the volume changes according to the temperature, the temperature at which the density has been found should be placed alongside the density-figure. With the assistance of the expansion coefficient the density-figures for other temperatures can then also be determined. The densities are generally referred to 14° R. 17.5° C. For the practice sufficiently accurate results are obtained by taking 0.001 change of density for 1° R., the correction being added with oil of a temperature over 14° R., and subtracted with oil below 14° R. Thus for instance the density of a crude oil of 20° R. has been found as 42° B. 0.8139, which corrected would be (6x0.001--0.006) 0.8145.

These corrections are of importance, especially in the refining process, for the accurate determination of the commencement and ending of the kerosene fraction.

The expansion coefficient varies, according to investigations by W. Markownikoff and W. Ogloblin, with petroleum from different regions, it being in an inverse ratio to the density. This agrees also with experiments made with North American oils, which gave the following results: