they pass to the reservoirs. An extension of the coil traverses a water vessel, E, for condensation of the lighter oils. A pipe, F, is provided for the discharge of the residue, and inlets, a and b, are for the admission of steam and oil respectively. A manhole is shown at c, and the heating furnace, with flues, at d, e, f, g, h, i.

When the oil in the still is sufficiently heated, as is shown by its even ebullition and by the appearance of drops of distillate, superheated steam is introduced and distillation commences.

In order to separate the distillate into its various fractions, and to remove as much of it as possible free from condensed steam, it is now usual to employ condensing appliances of special form, with outlets for running off the different fractions, and one of the best of these is stated to be the Albrecht condenser, C, illustrated in the figure. It is provided with three outlets, as already mentioned, and consists of tapering tubes which are formed of welded sheet-iron, the diameter at the

larger end being about 20 centimetres, and at the smaller 8 or 10 centimetres. Each tube is 6 or 7 metres long, and the aggregate length is 40 to 50 metres. At the commencement of the distillation, light oils flow from the first outlet, but soon the other outlets begin to discharge, and the variation in specific gravity between the different fractions thus obtained is from 0.005 to 0.015. The heavy distillates from the first and second outlets are free from water, while the lighter oils contain it, and at the extremity of the condenser, nothing but steam escapes. The steam superheater is heated some hours before use, and the steam is passed continuously through it until it no longer condenses at the testing tap. The supply of steam requires careful regulation to prevent portions of the residue in the still being carried over with the oil. The steam is distributed through a branched tube so perforated that part of the steam is directed upon the bottom of the still to prevent the oil from burning

against the plates, while the remainder is evenly distributed. The temperature at first varies between 130° and 200° C., and is increased as the distillation progresses, to 250° or 300°, but not higher. In many refineries, 200° is the average temperature employed, but this is somewhat increased in winter. The quantity of steam used is variable, but is generally such that the proportion of water to oil in the condensed product is as 1 to 2, or at the highest, 1 to 1.

The vacuum process of distillation of lubricating oils is now in very general use, especially for obtaining the heavier products. Fig. 103 exhibits the application of Körting's steam-jet exhauster to a direct fired still, D. The vapours from the still pass through a worm condenser, K, into a receiver, C, which is in communication with the exhauster. The action of the exhauster is due to the passage of a jet of steam, admitted through a tube, a, over a row of conical nozzles.

The steam supply is regulated by a valve controlled by a hand wheel. The oil vapours from the still are condensed, and collect in the receiver, C, whence they are drawn off from time to time by a tap, B, while the steam escapes through a pipe, L. Wanklyn and Cooper have recently devised1 an apparatus, in which distillation can be conducted at reduced pressure without the use of an exhauster, a partial vacuum being produced by carrying a pipe downwards from the receiver to a vertical distance of 40 feet.

The dome into which the vapours pass before entering the condenser, serves to arrest the oil particles which have been carried up mechanically. Its size varies with the nature of the oil treated, a larger dome being used for the distillation of crude oil than for treatment of residue, because, in the former case, a partial condensa

tion of the vapour in the dome is desirable, while in the latter case a rapid removal of the vapour is aimed at. The dome is placed at the end of the still nearest to the condenser, and the vapour is conducted either through a single tapering tube, or through a number of tubes, as many as forty being provided in the case of the cheese-box still shown in Fig. 87. The connecting tubes are in some instances inclined towards the dome, in order that the heavy oils which condense in them may run back into the still.

Condensers of many different descriptions are used, the most common forms being those in which the vapours traverse parallel or coiled pipes of large condensing surface. Water is the cooling medium generally adopted, although in some cases, especially when there is danger of the water freezing, crude oil or residue is employed for cooling, and is thus partly heated before passing to the still. In some cases (as, for instance, in the production of machine oils), the exposure of the pipes to the air serves for condensation, but a very large condensing surface is then required. It is stated that air condensation requires nearly 200 times the condensing surface necessary when water is used. Under certain circumstances, it is necessary to keep the condensing water warm, or even almost boiling, in order to prevent the paraffin from solidifying in the pipes. The worm condenser is very largely employed, but the old spiral form is usually replaced by a worm consisting of straight tubes connected by elbows, and passing along the sides of a square tank made of iron, or less frequently, of wood, through which the water circulates from below upwards. The condensing surface varies with the size of the still. According to Veith,2 a still of 500 to 700 barrels capacity should have a series of condensing tubes of a total length of 300 metres, and an average section of 15 centimetres. The pipes may diminish in diameter from 20 or 25 centimetres where the vapours enter, to 5 to 8 centimetres where the condensed product escapes. Fig. 104 shows an ordinary worm-condenser, S, fitted with an arrangement for classifying the distillates. The condensed liquid passes into a U-tube, U, forming a seal, which prevents the passage of uncondensed gas, and diverts it into an escape pipe, G. The liquid passes into a tank, K, from which the condensed water, which separates, is drawn off from time to time through a tap, h. The oil flows through a pipe, a, and a separator, L, consisting of a cast-iron pipe, with several branches connected through taps, hy h2 h, &c., with pipes which lead to storage tanks. The tank, K, is fitted with a window so that the colour of the distillate may be observed, and the distribution of the products controlled, the different qualities being directed into their respective tanks by opening the proper taps. Taps are fitted to the bottoms of the U-tube and of the tank, K, for running off sediment.

A cast-iron tube condenser allied to the above has been described by Engler. It consists of four horizontal rows, each of six parallel Veith, Das Erdöl, 141. 2 Loc. cit., 142.

3 Dingler's polytech. Journ., cclx., 438.

tubes varying from 14 to 20 centimetres in diameter, and having a total length of 60 to 100 metres per still.

Where space permits, the parallel tube condenser is preferred. This consists of a long wooden tank to hold water, through which a number of condensing tubes are carried with a slight fall. Fig. 105 shows the end of the tank at which the tubes, a, issue near the bottom. The distillates flow through a siphon into a series of parallel troughs, R, in communication with a stop-cock, H; while the incondensable gas, which is arrested by the siphon, passes up the vertical pipes, 91, &c., through the cocks, h, &c., into the horizontal pipe, G, whence it is conducted into a gasometer, or is allowed to escape into the air at L.

A form of box condenser, consisting of a closed vessel, in which the vapours are condensed by water traversing iron tubes, is employed by Nobel Brothers in their refinery at Baku. The Lawrence system of surface condensation, which is employed successfully in some refineries, consists in the use of a flat box, formed of two sheets of corrugated metal placed close together and joined at the edges. The vapours circulate between the plates, and are condensed by cold water which trickles over the outside. The arrangements adopted for condensing the various fractions obtained by the redistillation of naphtha are described later on.

As already stated, the continuous system of distillation, though largely used in Russia, is not employed in the United States. It has, however, attracted considerable attention in the latter country, as the