The distiller is shown in section in Fig. 22, and consists of a lead glass tube a b 36 in. long and about 3/8 in. internal diameter. About 2 in. from its closed upper end is blown a bulb about 2 In. diameter. The lower end passes through an air-tight cork of rubber, closing the top of the cistern dc, and ends at 6, a little belowthe tube f. The cistern dc is made of glass tube 1 in. diameter and 12 in. long, and has two short pieces of " quill " tubing of sealed into it. The lower end is also closed by a cork, through which passes a piece of Sprengel tube i 36 in. long, and having a piece of quill tubing h about 24 in. long sealed into the upper end. The top of this tube is nearly in contact with a. The internal diameter of the Sprengel tube should not much exceed 1 mm., and the bend of the lower end is best when not much more than 1 in. radius.

Dessicating Mechanical Methods Continued 50014Mercury still.

Mercury still.

The base of the stand is a wooden tray C D, from which rises a board D E, carrying a shelf A , perforated in the centre with a hole allowing the glass bulb to pass through it. A large cork F is bored with a hole of rather less diameter than the tube a 6, and the cork is cut in halves. The tube is held in position by twisting a piece of copper wire round the halves of the cork. The cistern is secured by string passing through holes in the projecting piece of wood B. A block of wood serves to support the end of the tube i, and a tin cylinder notched round the top, and covered with a flat tin plate, keeps the bulb surrounded with hot air, while a mica window at the side allows the height of the mercury in the bulb to be easily seen. The pipe of the brass ring burner passes through a hole in the tin gas plate, and the ring, slightly larger than the bulb, is perforated on its inside with many holes.

The constant level reservoir is a large glass bottle provided with a tubulure at the side. Similar bottles are now made for the mercury pumps of electric incandescent lamp manufacturers. Into the tubulure passes a glass tube k about 3 in. long and 1/2 in. diameter. Its outer end is closed, and into the upper and under sides are sealed two pieces of quill tubing Ij. The top of the upper end is open, but the lower j is connected with the cistern of the distiller by a narrow piece of rubber tubing m, about 3 1/2 ft. long, inclosed in a canvas tube. The " thistle " funnel t and small glass stop-cock S are also fitted air tight into the bottle by "a rubber tube. The reservoir is placed on an adjustable table stand on the shelf H.

To set the distiller in action, the stopcock S of the reservoir is opened, and some mercury is poured through the thistle funnel t into the reservoir, while, with a short piece of rubber tubing and glass rod, the tube e is closed securely (Fig. 22) at the top by the cistern. Then the reservoir is raised. The mercury gradually rises in the cistern, and by compressing the air in the upper part is forced up the tube a b, and then filling the bulb "sprengels " down the tube hi. The reservoir may then be lowered to its stand on H, and the rubber stopper removed from the tube e. The reservoir is set in action by attaching a piece of rubber tube to the stop-cock S, and sucking out air until, passing down the tube /, it bubbles up through the mercury in the reservoir. Then the stop-cock is closed, and the reservoir is adjusted at such a height in the stand that the mercury is nearly at the top of the bulb in the distiller. Thus set in action, the level of the mercury in the cistern cd will be kept constant until almost all the mercury has been distilled.

To start the distillation, the tin plate which covers the cylinder H is removed, and the gas is lighted. A few minutes later sufficient mercury will have distilled over to displace the impure mercury originally present in the narrow Sprengel tube i.

The reservoir is replenished with mercury without interrupting the distillation, by placing a screw pinch-cock on the rubber tube leading to the cistern of the distiller, opening the cock S, and pouring the mercury into the reservoir through the funnel t. Then a few bubbles of air are sucked out of the reservoir as already described, the stopcock is closed, and the screw clamp is released from the rubber tube. The level of the mercury in the distiller remains as before.

Such an apparatus as that illustrated will distil about 2 lb. of mercury per hour with an expenditure of very little gas. Zinc, cadmium, magnesium, and other metals may also be distilled by the same plan.

Water

The arrangement shown in Fig. 23, is one that may readily be adapted to, and is specially suited for, the old fashioned stills which are in frequent use among pharmacists for the purpose of distilling water. The idea is extremely simple, but thoroughly efficient in actual practice. The still is of thin copper, 2 gal. capacity, and the condenser is the usual worm surrounded with cold water. The overflow of warm water from the condenser is not ran into the waste pipe as in the ordinary coarse, hut carried by means of a bent tube A, B, C, to the supply pipe of the still. The bend at B acts as a trap, which prevents the escape of steam. The advantages of this arrangement are obvious. It is perfectly simple, and can he adapted at no expense. It permits of a continuous supply of hot water to the still, so that the contents of the latter may always be kept boiling rapidly, and as a consequence it condenses the maximum amount of water with the minimum of loss of heat. If the supply of water at D be carefully regulated, it will be found that a continuous current will be passing into the still at a temperature of about 180° F., or, if practice suggest the desirability of running in the water at intervals, this can be easily arranged.

It is necessary that the level at A should be two inches or thereabout higher than the level of the bend at C, otherwise there may not be sufficient head to force a free current of water against the pressure of steam. It will also be found that the still should only contain water to the extent of about 1/4 of its capacity when distillation is commenced, as the water in the condenser becomes heated much more rapidly than the same volume is vapourised. By this expedient a still of 2 gal. capacity will yield about 6 gal. per day, a much greater quantity than could ever be obtained under the old system, which required the still to be recharged with cold water every time l 1/2 gal. had been taken off. The objection to all such continuous or automatic arrangements is, of course, that the condensed water contains all the free ammonia that may have existed in the water originally, but it is only in cases where the water is exceptionally impure that this disadvantage will become really serious. (T. Maben.)