facilitate the "cracking" or destructive distillation of the oil. A double fire-box is built under the front quarter of the still, but, by having the flue for the exit of the gases of combustion in the rear, the heat is applied to the whole length of the bottom and well upon the sides of the cylinder. The still is also provided with man-holes, with steam-pipes of various plans, charging and draw-off pipes, gauges, vacuum and pressure valves, etc.

Another form of cylinder still is shown in Figs. 80 and 81. The still is suspended to the brackets P, while both ends of it rest upon brickwork. The gases of combustion pass in the direction of the line Z-Z,, below and then above the arch C,

ascend in two lateral flues and then enter the tubes K. In these flues they pass through the still in the direction of the line Z-Z, and enter the chimney at the back. The tubes K of riveted sheet iron are, on the one hand, connected with the lateral tubes, and, on the other, pass through the front plate of the still. They traverse the entire length of the still, pass out through the back plate, and enter the chimney. When the

still is filled and in operation, the gases of combustion traverse the described passage; they ascend in the lateral flues and, the slide 7 being open and the slides T, and T, closed, they pass through the tubes and reach the chimney. When distillation has progressed so far that the level of the oil is below the tubes, the slide T is closed and the slides T, and T, are opened; there being no draught in the tubes, the gases of combustion then

pass directly into the chimney. The whole arrangement is very advantageous, it allowing of a ready regulation of the operation and thorough utilization of the heat. It has, however, the disadvantage of the operation being more dangerous. The heating tubes must be very carefully made, otherwise they may become leaky and constitute a source of danger from fire. This form of still is suitable for working larger quantities of oil, and the heating being very intense, it may be given a capacity of from 400 to 700 barrels. The thickness of the boilerplate for constructing the still should be in accordance with its capacity and somewhat greater than for other stills, since the arrangement of the fire tubes requires a stronger construction. The still is provided with all other contrivances previously

described, such as man-holes, steam-pipes, gauges, etc. On account of its greater capacity the gas dome is larger and it is provided with a greater number of condensing pipes, generally from five to seven. The discharging contrivance with the valve E1, which is regulated from above, may be highly recommended. It consists of a round rod, which carries on its lower end a valve that fits in a valve-seat; the upper end of the rod passes through a stuffing box. For opening or closing the valve the rod is not turned, but lifted by means of a toothed gearing. This seemingly slight circumstance is of great importance, since, if the rod were turned and not lifted, it might be readily twisted in consequence of changes of temperature in the still, whereby the valve would be rendered useless. For indicating the level of the fluid in the still in some refineries a contrivance S is used, which will be described, without, however, recommending its employment.

The arrangement is readily understood from the illustration. On the outside of the still a vertical pipe is connected by a horizontal pipe with the lowest point of the still. On the vertical pipe, at determined distances from each other, are small testcocks; by opening these cocks the level of the fluid in the still may be ascertained. The disadvantages of this arrangement may be readily understood. In order to control it the tube. must be placed on the front of the still, hence near the position of the stoker. By the careless opening of a cock or leakage of the connections, the oil may readily reach the fire and ignite; thus a fire was actually caused in a large Buda-Pesth refinery.

The so-called wagon still derives its name from its resemblance to an American passenger railway car. Figs. 82 and 83 show a form of this still used in Baku. It consists of the boxlike still A, of wrought iron plates riveted together. It is 23 feet long, 14 feet in diameter and 10 feet high (counted from the deepest part of the bottom to the dome). It is provided with three domes a which convey the vapors to the condenser; b is a man-hole, and c three pipes for the discharge of the residuum. The arrangement of the stays in the interior of the still,

as well as the brick work with flues B and B, is plainly shown in the illustrations. In order to protect the bottom of the still

tected by fire-bricks, to the front, ascends, turns on both sides of the still, first backward then downward and escapes into the chimney through the flue B

With a capacity of such a still of over 77.000 lbs., and a charge of 66,000 lbs. of crude oil. 2 distillations, hence 154,000 to 176,000 lbs. of Russian crude naphtha, can be distilled in 24 hours, which corresponds to a daily production of from 44,000 to 55,000 lbs. of illuminating oil from Caucasus crude oil.

The wagon still shown in Fig. 84 has a length of about 46 feet and a capacity of 2,500 barrels. To utilize the heat or the hot gases to the best advantage, the bottom has three trayformed depressions, in each of which lie two flues F. The flame strikes at E backward beneath the bottom, then forward

through both the flues, and passes into a chimney. Each depression is provided with a fireplace and chimney, and has on the front side a tar-hole, which is closed like a manhole, and serves for the discharge of the residuum. The cap A carries on the end opposite the fire-place the pipe conveying the supply of crude oil, and running its entire length, a headpiece, B.