In Pennsylvania the oils of various densities run into one tank, the result being an average oil; hence it is customary to allow an expansion coefficient of 0.00072 for 1° C. (0.004 for 10° F.)

From the subjoined table, compiled by Dr. H. Gintl, the above-mentioned relation between the expansion coefficient and the density may also be recognized:

A detailed table of expansion of West Virginia Natural Oils has been calculated by J. Schubert.'

For practical purposes a knowledge of the expansion coefficient is of importance, especially for calculating the so-called expansion-spaces in the packages in which the oil is shipped.

Optical properties. Color, transparency and lustre have previously been mentioned. It remains only to be stated that water-clear petroleum is of rare occurrence, for instance, in Persia and at Smith's Ferry, Pennsylvania. Transparent oils are distinguished by strong refraction of light and possess a blue flourescence, and the dark varieties a green fluorescence, which is frequently quite intense.

1S. F. Peckham, Report on Petroleum, p. III.

As far as at present kaown, petrzleum fces act turn the plane of polarization of a ray of light.

The action of light upon the ssior of perieum deserves also * se mentioned, that of white, bue and green light being strongest and sat of yellow, red and black, veakest By the action of light ozone is formed, which frequently appears by an exposure of a few hours only. By this change the illuminating Some of the oil is reduced.

Volatilization. By exposure to the air petroleum volatilizes paray, whereby it becomes denser, less mobile, finally viscous

vold. This explains the fact previously mentioned that pefre un from a greater depth is specifically lighter, and also that in the neighborhood of the outcrop it is frequently so visFors that it can be directly used as wagon grease, maktha or th metal fat hanng formerly been frequently employed for that purpose. Hence the only sure conclusion which can be drawn from the quality of the outcrop is that at a greater depth oil specifically lighter and, as a rule, richer in illuminating oil, thay be found,

The volatility of petroleum renders its storage in tight and well closed vessels necessary, and to avoid losses it should not be stored for a long time. In regard to this Nawratil has made some interesting experiments with a thinly-fluid crude oil from Blich near Gorlice, West Galicia, the specific gravity of which, fresh from the well, was 0.800. Kept in an open porcelain dish at the ordinary temperature for one month, its specific gravity was o Hos, and it was thickly-fluid. The fresh oil contained 9.3 per cent, light oils (distillate up to 212° F.,) while after several days' transport in a tight oak barrel it contained only 0.5 per cent, of these constituents. Hence there was a considerable loss, especially for the producer of the crude oil.

The gases evolving first from petroleum are very inflammable and mixed with air form an explosive combination. Hence great precaution against fire has to be used near the wells as well as in the store-rooms,

The great volatility of certain constituents of petroleum also

explains the difference in chemical analyses of petroleum from the same well, if the greatest care has not been exercised in taking and preserving the samples.

According to experiments by Dr. H. Gintl regarding the volatility of crude oil at the ordinary temperature of a room (61° F.,) the evaporation amounted:

Petroleum volatilizes the more readily the richer in hydrogen and the poorer in carbon it is.

Boiling point. With an increasing temperature vaporization becomes of course greater, until at a certain temperature gas bubbles appear, and at a still higher temperature the oil commences to boil. This boiling point varies and for most American crude oils lies, according to N. Tate, between 104° and 122° F. On the other hand, according to Balley and Schwarzenbach, Pennsylvania crude oil evolves gas bubbles at 89.6° F., and commences to boil at 134.6° F., while for Canadian crude oil these values are about 4° higher. With both varieties of oil, the difference in the two above-mentioned temperatures is 77° F.

However, according to Eagler, the boiling points of Pennsylvania crude oils are much higher, and are given together with those of other vaneties of petroleum in the table on preceding page.

The boiling print rises with the progress of vaporization, and hence is in a reverse ratio to the density. After storing there will, therefore, be considerabile varations in such determinations of a petroleum from the same origin.

Physiological properties. Petroleum has an arcmatic odor disagreeable to many persons. Some varieties, for instance, Canadian. South American and West Indian crude oils, have, however, an offensive oder which appears to be due to a small content of sulphur.

Water shaken with crude oil acquires the odor of the latter. The vapors arising from petroleum are in some regions, for instance in Pennsylvania, considered beneficial for persons suffering from lung troubles, but, according to Poincare, workmen employed in distilling crude of complain frequently of irritation of the mucous membrane of the nose. Investigations by Poincaré showed that guinea-pigs kept in such an atmosphere died in one or two years, and rabbits suffered from somnolence and loss of appetite.

CHAPTER IV.

CHEMICAL CONSTITUTION OF PETROLEUM.

PETROLEUM consists essentially of various hydrocarbons belonging mostly to the methane series (CH2 + 2) or also corresponding to the type C.H2, both groups being indifferent to mineral acids. In the oils of one region there is a decided preponderance of the members of the one or other type, in addition to which there frequently occur in very small quantities members of the aromatic series, and here and there combinations of nitrogen and oxygen. The inorganic portion is also exceedingly small.

Petroleum has been frequently subjected to analysis. It has been stated that gold in small quantities has been found in the ashes of crude petroleum and in the residuum of petroleum stills. Sulphur exists in small and varying proportions in almost every variety. It is frequently noticed in the exit pipe conveying the gas from the stills in refineries, in such quantities as sometimes to effectually close the pipe. Metallic arsenic also, it is said, has been noticed to condense in the goosenecks of the retorts in which the bituminous limestones of Lobsan are distilled.

In the subjoined table most of the elementary analyses known are given, for which we are chiefly indebted to St. ClaireDeville (D.), Boussingault (Bo.), Baumhauer' (B.), Gintl (G.), S. F. Peckham (P.), Gulischambaroff (Gn.), Markownikoff and Oglobin (M. O.)

Wells of the same region in close vicinity to one another frequently yield entirely different oils.

The subjoined table shows that Peckham and Markownikoff and Oglobin could not establish a content of oxygen, while the former found nitrogen.