used for the purpose. The oil vapors mixed, with the steam, ascended, passed through a tall head, then through a cooling coil, and after condensation were refined in the usual manner. However, the products obtained by this process did not answer all demands. Hence it was endeavored to obtain good and faultless products by modifying the shape of the still, by selecting the proper material, the perfect superheating and introduction of the steam, and finally by the proper condensation of the vapors.

The separate modifications may be described as follows:

First it was learned from experience that cast iron stills did not answer the purpose, it being very difficult, in consequence of the thickness of the material and its slight capacity of conducting heat, to bring the still to a temperature at which, on the one hand, the oil would be properly heated, and, on the other, the introduced superheated steam would not condense. The oil remained cold and a considerable portion of the steam condensed, which frequently caused the oil to run over and produced irregularities in the process of distillation. If in the course of the operation the still became sufficiently heated it was very difficult to cool it off and regulate the temperature-a circumstance of great importance in this mode of distillation. Sheet iron stills were then successfully introduced; they being thinner, all the above described evils could be avoided. oils obtained were fatter and lighter, but not free from odor. The principal reason for the latter defect was the use of upright stills, the distance the oil vapor had to ascend being disproportionately large to the vaporizing surface. The oil vapors carried along with the steam were forced to traverse a great portion of their way in the still itself, and becoming partially condensed on account of their high boiling point, they flowed back generally on the strongly heated sides of the still, where they suffered decomposition, though to a limited degree. This was the case especially towards the end of distillation, when the heaviest and fattest oils were obtained. This led to the adoption of horizontal cylindrical stills, a form which with slight modifications

The

(oval cross-section) is now in general use in all Russian and modern European factories. When the importance of rapidly carrying away the oil was recognized, it was provided for by low domes and discharge-pipes with considerable fall.

In modern times distillation with superheated steam is assisted by a vacuum.

Fig. 107 shows the arrangement of a distilling plant without the use of a vacuum, together with the condensing apparatus. A is the oval still; B, the dome; C the pipe for the oil-vapor. The pipe C has the form of a coil with a constant fall; its diameter at the initial point is 1534 inches, but is gradualiy reduced. At the points 1, 2 and 3, are pipes for the condensed oils,

which run into the three pots D, and from there into the reservoirs. E is the cooling coil for the lightest products, F the discharge pipe for the residues no longer fit for distillation; a and b are openings for the introduction of steam and oil; c is the man-hole, and d, e, f, g, h, i, the heating arrangement together with the smoke flue.

Distillation is carried on as follows: When the residuum is sufficiently heated, which is recognized by its boiling uniformly and the appearance of drops of the lightest oil, steam is immediately introduced.

The superheater is heated a few hours before commencing

operations, and the steam allowed to pass continuously through it. The steam is sufficiently heated to allow of its introduction into the still when it loses its white-gray color, and appears at the test cock blue and transparent. It should be introduced slowly and gradually, otherwise it might carry along not only oil but also residuum. Its admission is regulated by partially opening the steam-valve in front of the still and closing to the same extent the valve on the pipe which allows the steam to escape into the open air. Distillation commences immediately, and opening and closing of the two valves is continued until distillation proceeds quietly and vigorously. The steam enters the still through a forked pipe, the holes in which should be so arranged that while a portion of the steam passing out is forced to flow along the bottom of the still to prevent scorching of the oil and to expel the last heavy remnants, another portion flows partially in a lateral and partially in an upward direction. In the beginning of distillation the temperature of the steam varies between 266° and 390° F., but as distillation progresses it is raised to between 482° and 572° F., but never above the latter point. Many factories work with an average temperature of 392° F., it being slightly raised only in winter.

The quantity of superheated steam used varies, but as a rule it suffices when in the product of condensation, the quantity of water is in the proportion of 1: 2, or at the utmost of I: I to the quantity of oil.

The next important operation is condensation, the good quality of the oil largely depending on it, because notwithstanding the use of horizontal stills and sufficiently and properly superheated steam, the oils were formerly not entirely satisfactory. In Russia, especially in the Nobel and Ragosin factories, a system has been introduced which is based upon the proper conception of the physical elements of distillation. While in nearly all the older refineries condensation of the oil vapors and steam is effected in the old method by allowing them to pass through one or at the utmost two pipes and then

cooling them by water, the modern process is based upon separate cooling by air and water.

The action of the steam being purely mechanical, since it vaporizes the lighter portions of the oil and carries along the heavier portions, it is evident that with the old process of condensation, these vapors and particles of oil condense and combine in the pipe and the resulting oil does not possess a great degree of viscosity and a high igniting point. By allowing, however, this mixture of oil vapors and steam to circulate in properly constructed pipes, and providing discharge pipes at suitable places, the heaviest oils will first separate and run off, next those which condense with greater difficulty, and so on. Thus with a proper apparatus oils with different specific gravities of varying degrees of viscosity and with different boiling points, can be obtained at the same time and alongside one another. The idea of aërial condensation, especially for light oils, is, however, not new.

Every well arranged refinery has now introduced separate condensation, whereby the vapors are separated according to their volatility into fractions by dephlegmators cooled by air. M. Albrecht's aërial condenser, seen in Fig. 105, is much used. It consists of patent welded sheet-iron pipes about 734 inches or more in diameter, which gradually taper to 3 or 4 inches. Each pipe is from 20 to 23 feet long, the total length of the pipes varying between 131 and 164 feet.

The oil vapors condense in such a manner that in the beginning of the operation light oils appear at the first discharge pipe, but in a few hours the flow regulates itself, so that a natural separation of the oils is maintained up to the end of distillation. The difference in the specific gravities of the fractions varies between 0.005 and 0.015, according to the length of the condenser. By this method of condensation the oils running off at the first places of discharge are obtained almost free from water, a larger quantity of water condensing only with the lightest oil, while pure steam passes out from the terminal point of the coil. Hence the oil does not require much time for settling and can in a short time be used for refining.

Mr. Benjamin J. Crew describes a condenser in which water condensation is supplemented by an arrangement for aerial condensation. The apparatus is rigged immediately above the water tank and rests upon it. In the winter season it adds very materially to the condensing surface, besides affording an easy, rapid method of dividing the products of distillation at one operation into at least three distinct gravities of oil or benzine.

Fig. 108 will illustrate this form of aërial condensation:

Fig. 108.

A

B

F

M

A represents the large pipe leading direct from the still and connecting this with the condenser. B, the first air condenser, is an iron cylinder of three-sixteenth iron, 30 feet in length, 24 inches in diameter. C, is an elbow connection between B and the second condenser D, of same diameter as the first. E is an elbow connection between the second condenser D and the third condenser F. G is an elbow connection between the third air condenser F, and the usual condensing pipe H, which here enters the water in the tank I.