II. THE SPECIFIC GRAVITY OF PETROLEUM

Is ascertained by the use of either one or the other of the instruments here described. Fig. 55 represents the ordinary hydrometer graduated according to the Baumé scale for liquids lighter than water. Fig. 56 represents the combined hydrometer and thermometer. Fig. 57 represents the vessel usually employed for holding the oil, and is known as the hydrometer jar. The only other instrument employed for this purpose is the one-thousand-grains bottle represented in Fig. 58. This bottle is filled, accurately up to the mark on the neck, with the oil to be tested. This instrument has been accurately gauged and marked to contain 1000 grains of distilled water at a temperature of 60° F. It is, therefore, necessary, before the oil is placed in this bottle, that it should be carefully brought to the same degree of temperature. After filling, the bottle and contents are weighed in a delicate balance, and the specific gravity thus determined. It is also designed, in the use of the hydrometer, that the oil should be of the same temperature (i. e. 60° F.), and, if it is either above or below this point, a certain correction must be made. In the earlier days of

the manufacture of petroleum, it was customary to allow a change of one degree of Baumé's hydrometer for every ten degrees of temperature. For example, a sample of oil testing 45° B. at 50° temperature, would be considered as

Fig. 55.

Fig. 56.

Fig. 57.

Fig. 58.

Hydrometer and Thermometer combined and Test Jar.

having a gravity of 46° B. at a temperature of 60°, or a gravity of 44° B. at 40° F. Much more accurate computations are now made, and elaborate tables accompany the case of Taliabue's delicate hydrometers which are graduated to a scale of degrees in tenths.

The following table will be found extremely useful in converting Baumé markings into true specific gravities. This table refers only to liquids lighter than water. are similar tables for liquids heavier than water.

There

For Liquids Lighter than Water. (Temp. 60° Fahr.)

Baumé. Specific gravity. Baumé. Specific gravity. Baumé. Specific gravity.

This term very vaguely describes what has been supposed to be the most desirable quality of a lubricating oil. The word viscidity, a complete synonym, throws no further light upon its real meaning. While it bears an important relation to lubricating oils, it by no means follows that the most viscous oils are the best lubricators for all purposes,

but it is true, that, in determining the value of mineral lubricants, those with the greatest viscosity are to be preferred. Concerning the general qualities of lubricating oils, and the methods employed in judging their value, we refer our readers to the chapter especially devoted to that subject. We propose, in this connection, simply to describe the method of determining the viscosity of an oil. Animal and vegetable oils are generally more viscous than mineral oils, and, while this property is closely related to the specific gravity, it is not directly proportional to it; vegetable oils are more viscous than animal oils, and the measure of viscosity of oils at ordinary temperatures is not to be assumed as a standard of the same oils at higher temperatures. "Tallow and castor oils are more viscous than sperm when cool, but they become very much more fluid when heated as in steam cylinders." There are two methods of determining the viscosity of an oil:

1st. By observing the length of time a measured sample of oil will require to pass through the small orifice of a pipette. The greater the viscidity of an oil, the longer the time it will require for the oil to pass through.

2d. By observing the length of time a sample of oil takes to pass from the top to the bottom of an inclined plane of glass or polished metal.

A very complete instrument (pipette), represented in Fig. 59, is thus described by Prof. Thurston.

1 Thurston, On Friction and Lost Work.

In the figure A is a glass-tube about 1 inch in diameter, graduated from 1 to 100, to contain about 100 cubic centimetres of oil. BB is a glass jacket about three inches in diameter, filled with water as shown. C, a thermometer indicating temperature of water in jacket. D, a small brass cock for withdrawing water from jacket. E, a glass flask for generating steam to heat water in jacket. F, a glass pipe connecting the steam flask E with jacket B, delivering at bottom of jacket. G is a small cock for permitting an escape of steam in order to regulate the amount sent into jacket. H, a spirit lamp on a stand. J, a glass beaker to contain oil, and K, cast-iron stand, with adjustable arms, for carrying the apparatus.