The distillation of all the benzene products is effected by the introduction of a steam coil near the bottom of the still. In large refineries where the benzene product is very large, the ordinary alcohol column still is quite inadequate to meet the demand made upon it. A modification has been employed including an enlarged form of this apparatus.

The stills used in this connection may be constructed either upon the principle of the cylinder or the cheese-box still, previously described. They are built of wrought iron, and, resting upon a stone or brick foundation, do not require any arrangement for fire places. In large works they are frequently constructed to hold one thousand barrels. The product of this distillation is then distributed in one operation into three different receptacles. The heavier portions, below 62°, are run into the oil tank.

THE DEODORIZATION OF BENZENE

Is effected upon the same general principles which regulate the deodorization of oils, excepting that the agitation is effected by a revolving paddle. The blower is inadmissible here on account of the great loss of material by volatilization. The proportion of oil of vitriol used is also much smaller. One half of one per cent. is ample to effect a thorough deodorization. This deodorized product is generally employed for detergent purposes, for the extraction of grease from all kinds of fabrics, and for other uses where the disagreeable odor of crude benzene is not objectionable.

THE DISTILLATION AND UTILIZATION OF RESIDUUM.

After all the oil that can be safely run into the illuminating oil has been removed from the still, and when the darkened product would impair or imperil the color-test, the fires are usually withdrawn from the still and preparations made to remove the residuum and the coke. Some refiners prefer to continue the distillation a short time longer to recover a small percentage of oil, dark though it may be, which is run over with a fresh portion of crude oil. Where the crude oil is of light gravity this proceeding is unobjectionable and may be profitable; but when the crude oil is of heavy gravity, the propriety is questionable, and its profitableness exceedingly doubtful. In former years it was customary to allow the still to cool for several hours after the fire had been withdrawn. The residuum was withdrawn through a tail pipe at the rear of the still. This could not be done immediately after the fire was withdrawn, as at the high temperature of the contents of the still at the completion of the process of distillation, the residuum would instantly take fire upon exposure to the oxygen of the atmosphere. Several dangerous fires resulted from this early mode of procedure. The residuum is now withdrawn by means of a pipe connected with a steam pump. The pipe passes by several returns of the same through a tank of cold water, which cools the residuum sufficiently to obviate this danger. It is pumped into a large settling reservoir or tank, where it is allowed to stand for several days to allow of the subsidence of all

the fine particles of coke, which will separate by this process. This tank is provided with an exit pipe placed at the distance of about twelve inches from the bottom of the tank, to admit of the drawing-off to the clear liquid, while a large opening or man-hole is placed on the side at the bottom to admit of the removal of the sediment. This is in the condition of slush, and is exclusively employed as fuel for the stills or boiler by mixing the same with fine coal dust or coke screenings. The residuum thus purified is pumped into storage tanks. In this condition it is either sold to the manufacturer of paraffine-wax and lubricating oils, or for the manufacture of gas, for which it has been largely employed, either to enrich the gas product of coal, or by itself.

TREATMENT OF RESIDUUM.

If there were any dividing line between the business of manufacturing illuminating oils and that of making lubri cating oils, this would be a proper place to make it, but in practice it is impossible to place this line, as it would be difficult to find two refiners who confine themselves exclusively to the same class of products; while some of the largest manufacturers who formerly devoted themselves entirely to one grade even of illuminating oil, now find it both convenient and profitable to handle most, if not all, of the various products which can be made from the crude oil. We shall therefore pursue the method which we have adopted, of describing the different processes employed, assuming for

convenience sake that all are practised under one manage

ment.

After the subsidence of all the coke, the residuum is transferred by means of a pump to the residuum stills. These are generally built on the cylinder pattern, and should not much exceed two hundred barrels' capacity, and are set in banks of three. In stills of larger capacity, it has been found in practice that the quantity of solid coke residue is so great that the heat necessary to drive the still to dryness is so intense as to severely strain the bottom, making frequent repairs necessary. The ordinary forms of condensers can be employed, excepting that the tanks containing the water are furnished with a steam pipe, in order that, in cold weather, the water may be warmed sufficiently to keep the dense paraffine oil passing through the pipe in a liquid condition; otherwise, the pipe may be so choked up with solid paraffine as to endanger the life of the operator from an explosion. In warm weather there is very little risk of this kind, but in extremely cold weather the distiller should be constantly on the alert to discover the first appearance of a stoppage from this cause. If, in weather of this description, the flow of oil is checked, with the ordinary fire under the still, the safest course will be to withdraw the fire, unless the condenser itself is supplied with a steam pipe by which a jet of live steam may be made to pass through the pipes and thus clean them.

In a number of paraffine-oil manufactories, air condensation is employed, and water tanks entirely dispensed with. The condensation is effected through cast- or wrought-iron

pipes of eight or ten inches in diameter, suspended in the air; the pipe rising by a slow gradation as it passes from the still. This pipe is provided with outlets at certain intervals to admit of the removal of the heavier oils, which are the most rapidly and readily condensed. This is, perhaps, a modification of the Atwood condenser.

When the still is loaded, and the fire started, the distillation commences. The first runnings from twenty to twenty-five per cent. (if the residuum be of good gravity), say of 20° to 21° B., will be found sufficiently light in gravity to be transferred to the crude oil tank and re-distilled from this. From that point down to the emptying of the still, paraffine oil constantly pours forth from the tail-pipe of the condenser, gradually deepening in color and increasing in density. If the paraffine oil is to be sold without further manipulation, the whole distillation is generally run into one tank, leaving the further manipulation to the manufactures of paraffine wax and lubricating oils. If the handling of the distillate is contemplated by the distiller of the residuum, another course is pursued, and we here merge our operations into the domains of the manufacture of lubricating oils and paraffine wax, which is in many places quite a distinct business. Here again is a subdivision of this multiform product. The manufacturer of wax selects his crude material from the various samples of heavy oil offered to him, being guided in his choice both by its gravity and color, and the percentage of wax it contains. The manufacturer of machinery or lubricating oils finds himself in a wilderness of oils of all kinds, animal, vegetable, and mine