time. If his still is driven too hard, however, minute particles of crude oil may be mechanically driven into the condenser, and seriously impair the color of the distillate long before the gravity of the oil should indicate a change of color. A difficulty in this direction is quickly and easily remedied by slackening the fire and thus reducing the outflow. In this part of the operation the still-man is guided almost exclusively by the color of the distillate. After about two-thirds of the contents of the still have passed over (and in crude oils of a gravity below 43°, this point is reached before this), there is marked increase in both the gravity and the color of the distillate. At this point all the experience and skill of the distiller are needed. The fire is slackened and the speed of the outflow is greatly reduced. The "cracking" process now begins, by means of which, with careful management, an excellent quality of oil is obtained until the still is emptied, leaving therein, in ordinary cases, about eight per cent. of residuum.

THECRACKING" PROCESS.

The history of the discovery and theory of the division of the heavier products of petroleum into a number of lighter ones is interesting and its importance cannot be over-estimated. It has largely increased the percentage of the yield of illuminating oil, thus enhancing the profit of the refiner. In a recently published volume on Petroleum Distillation, by Allen Norton Leet, I find the following account of the circumstances leading to the discovery of the "cracking" process.

"One cold afternoon in the winter of 1861-62, a sixteen barrel upright wrought-iron still in a refinery at Newark, New Jersey, was about half emptied of its contents and the distillate indicated 43° gravity with rapid tendencies toward lower figures and darker color, and the still-man intended in half an hour's time to cut off the remaining portion of the outflow into the heavy-oil tank. Having built a strong fire under the still, which supposably would keep the distillate in rapid motion for a time, the attendant locked up the refinery and went to dinner. It happened that after finishing his meal he was taken with a fit, and when he was sufficiently restored to resume work darkness had settled down upon the city. He had been away from the refinery for four hours. When he had struck a light, to his surprise and amazement, he found a small stream of oil still running into the distillate tank, quite cool, light in color and 48° in gravity. Failing to comprehend how the gravity and color could both lighten up after a large portion of the contents of the still had run off, and after a much lower gravity had been reached, and fearing something was wrong with the still, the still-man drew the fire, awaiting the coming of the proprietor. When the latter. arrived a thin stream still issued from the end of the worm, and to the surprise of both the specific gravity had risen to 52°. In order to study the effects of the internal operations of the still, he had a heavy glass retort constructed, and, then, by experiment discovered that after the distillation of the heart of the crude oil and when the gravity of the distillate had reached 44° with descending

Here

gradation, by reducing the temperature of the fire, the lighter vapors of what remained in the still would be carried over." By a close observation of the motion of these vapors he discovered that a portion of the product would be condensed by the cooler upper portions of the retort, and were returned to the oil of the retort. they were exposed to a higher temperature than was necessary simply for volatilization and were decomposed, giving rise to an increased yield of that grade of oil sought for. The theory was tested upon a larger scale in the iron retort which was adapted for the new mode of distillation by removing the brickwork from the upper portion of the still. The experiment was a success" to the delight and profit of the manufacturer."

The important results obtained by this changed method of distillation will be readily understood by an inspection of the table of the components of petroleum as analyzed by Pelouze and Cahours. In its natural state, according to this analysis, petroleum consists of a series of these hydrocarbons belonging to the paraffine series represented by the chemical formula, CH2+2 Hence we would recognize a hydro-carbon containing twice as many atoms of hydrogen (with the further addition of two atoms) as it does of carbon, as belonging to this series. We will take, for example, a sample of heavy oil represented by the chemical formula C1II, specific gravity .792, boiling at a temperature of 424° F. At a heat above its normal boiling point, when it is thrown back into the oil by condensation, it is decomposed into

13 289

One portion of the same series of oil represented by

carbon, deposited as coke, C

With

The portion of oil, C1H22, has the lighter specific gravity of .757 and a boiling point of 320°. This will be found to have the right color, and can be run into the burning oil; the gas passes off at the trap; the atom of carbon falls to the bottom of the still and is removed with the coke. careful distillation, by this process, 80 per cent. of burning oil may be obtained. Leaving for future consideration the re-distillation of the residuum and the first light products, we will take up the—

CHEMICAL TREATMENT.

It will be found that all the distillates are permeated with a peculiar burnt odor quite foreign to the crude oil, and evidently due to the heat employed and the partial decomposition of the oil. To remove this odor and to further decolorize the distillate, it is subjected to a treatment with sulphuric acid and subsequent washings with a solution of caustic soda and water.

In order to secure a "standard-white" color in a finished oil, the distillate should have a pale-straw color. If the distillation has been too rapid, it is liable to be tinged with a greenish-hue, which the acid will not discharge.

THE AGITATOR,

represented in Fig. 33, is constructed of iron boiler-plate, lined with sheet lead. Its size is commensurate with the needs of the establishment, and ranges in capacity from Fig. 33.

D

Agitator.

one hundred barrels to two thousand barrels. These agitators are generally deeper than they are wide, about in the proportion represented in the diagram. The bottom. is funnel-shaped, terminating in a pipe furnished with a stop-cock for drawing off the refuse acid and soda washings.