earliest applications of this principle being the oil filter or strainer of Wm. R. Warner, of Philadelphia (see Fig. 264). This filter or strainer consists of an upper cylindrical tinned-iron vessel, A, about twenty-two

FIG. 264.

A

inches high and ten inches in diameter, with a flange-rim soldered on the bottom, of rather less diameter, and about an inch wide, so as to fit firmly into the open top of another cylindrical tin vessel of the same diameter and eighteen inches high. The upper vessel is furnished with a lid, and with a tube and stop-cock, c, which penetrates the side close to the bottom, and fits into another tube, d, at e, which tube opens into the lower vessel close to its bottom and is secured to the side of B by a strong tubular stay. The filtering medium is a cone of hat-felt projecting upward from near the bottom of the lower vessel, and secured by thumbscrews passing through two tinned-iron rings and the felt, which are all properly pierced for the purpose. The stop-cock c being closed, the upper vessel is fitted in its place, and the tube-joint e rendered tight by wrapping twice around it a strip of isinglass plaster well moistened. When this is dry, the upper vessel is filled with the crude oil, and the stop-cock e opened, that the oil may flow into the open space below the filter. A heat of 120° F. is preferred to facilitate filtration or colation, and the filtered oil, as it accumulates in B, should be drawn off, as any large amount greatly retards the process by decreasing the force of the column bearing on the filter. For a pressure filter or strainer, Prof. B. S. Proctor uses a quadrangular cloth filter-bag securely tied to the end of a tin tube five feet long. The extremity of the tube has a wire ring soldered to it, to keep the bag from slipping off.

B

Warner's filter.

d

Continuous Filtration. Most of the expedients used in continuous washing (see page 209) are applicable to continuous filtration.

Filtration of Volatile Liquids. It is evident that the ordinary methods of filtering liquids will not be practicable for very volatile liquids, because of the loss through evaporation, and the liability to explosion, in the case of inflammable volatile liquids, if brought in contact with flame. Funnels must be covered, and provision made for the escape of the confined air in the receiving vessel. The following method is preferred to the elaborate expedients usually recommended. A glass tube (one of those usually sold as julep-tubes answers very well) is arranged in a glass or metallic funnel, so that the tube will lie close to the side of the funnel and allow one end to project above the filter, but not above the edge of the funnel: it may be held in its place by a ring of absorbent cotton gently thrust into the throat of the funnel. Or a rubber

cover perforated to admit a tube is placed on top, and connection between the bottle and funnel effected as shown in Fig. 265. For larger operations, Dr. Hadden's water-filter or Warner's oil-filter (see pages 224 and 225), slightly modified to suit the liquid, might be used. A very neat method of filtering volatile liquids is provided in the apparatus contrived by E. H. Hance, of Philadelphia. This consists of a cylindrical vessel provided with a tubulure and stop-cock below, and a ground-glass cover above; a flange near the top affords support for a perforated filter-support or funnel containing a filter. When not needed for filtration, the receiving vessel is very useful for many other purposes. Hot Filtration. This process is not resorted to as frequently as it might be with advantage, because of the difficulties which are asserted

FIG. 265.

to attend it. These have been greatly overestimated, for by the use of simple, properly-contrived apparatus many preparations which heretofore have been dispensed, bearing an unsightly cloudy appearance, can be greatly improved. Yellow wax is frequently full of mechanical impurities; ordinary straining will not deprive it of these, but it may be filtered through paper and thoroughly purified. Jellies, benzoinated

lard, petrolatum, cerates, ointments, etc., may thus be filtered. One of the simplest and most easily managed forms of apparatus (see Fig. 266) is made by filing off the ring from one of the ring-supports

of a retort-stand, J, and slipping on to the arm a brass circular jet, V, attached to a tee carrying the gas-supply pipe, A. A tinned-copper or tinned-iron funnel is supported by an appropriate ring at a suitable

FIG. 267.

Jacketed funnel.

distance above the jet. The filter is placed in the funnel, a receiving vessel adjusted below, and the hot liquid poured into the filter. It is plain that the liquid can be heated to almost any degree, and the filtration conducted at a much higher temperature (if need be) than by the jacketed hot-water funnel (see Fig. 267), and, on the other hand, the heat may be regulated so that it will be very moderate. The hot-water funnel is an old device, and consists simply of a jacketed funnel having a wide tube soldered at the lowest point, and an opening in the upper edge for the water-supply. A burner or a lamp-flame

will heat the water contained between the funnels, and a regulated heat not exceeding that of boiling water is obtained (see Fig. 267).

A modification of Dr. Hare's hot-water filter, which permits the use of glass funnels of different sizes, is shown in Fig. 268. It is simply

FIG. 268.

Hot filtration.

a tinned-copper box, with two sides shaped like a trapezoid, and supported upon four legs. There are three one-inch tubulures in the bottom, and the top has three openings which centre with the tubulures; beginning with the deepest, the diameters are four, three, and two inches. Three glass funnels of different sizes are selected, and the corks for the tubulures in the bottom, having been chosen, are perforated so as to permit the necks of the fun

nels to pass through and form perfectly tight joints. Water is placed

in the box and heated by the burner, as shown in the cut.

When

not needed for hot filtration, solid corks may be used to close the tubulures, and the box used as a water-bath, covers being placed over the openings which are not in use.

Rapid Filtering Apparatus. Of late years much attention has been expended upon methods of increasing the rapidity of filtration. Most of the plans suggested depend upon the principle of filtering into. a partial vacuum, but the means used to obtain this vacuous space are very varied. A simple method, applicable to operations on the small scale, consists in fitting a good cork to a wide-mouthed bottle and perforating it so that the neck of a funnel will accurately pass through it; another perforation permits the insertion of a piece of glass tube of small diameter. A plain filter of well-washed coarse linen or muslin cloth is then carefully adjusted in the funnel, and a plain filter of paper placed upon it. The liquid is poured upon the filter, and, a rubber tube having been fitted to the glass tube, suction is applied by the mouth. By pinching the rubber tube a partial vacuum is maintained in the bottle, and filtration is hastened. An improvement upon this would be to use a rubber stopper instead of cork, and instead of pinching the rubber tube to use a screw pinch-cock.

Water-Pumps acting by a Fall of Water.-One of the first practical efforts made in the direction of using water-power was seen in Bunsen's pump. The action depends upon the principle that a column of water descending through a tube from a height is capable of sucking with it the air contained in a lateral tube, if the latter is properly arranged. A cheap home-made apparatus, which depends upon a fall of water for its usefulness, is shown in Fig. 269. It consists of a common wide-mouthed half-gallon jar, and a tinned-iron can holding three, four, or five gallons; a castor-oil can answers very well. The screw-cap is for readily filling the can; the exhaust-pipe on the right reaches inside of the can, nearly to the bottom, the other tube is soldered on the head of the can connecting with

the interior. The jar, having a funnel fitting FIG. 270.
into it through an air-tight stopper, is con-
nected with the can by means of a bent glass
tube and rubber tube. The can is filled with
water, and the solution to be filtered is placed
in the funnel. The exhaust-pipe is connected

FIG. 269.

FIG. 271.

Rapid filtration,

Lux's aspirator.

Rapid filtration.

with a rubber tube eight or ten feet long and a quarter of an inch in diameter (the longer the tube the more rapid is the filtration). When the

syphon thus formed is started, the flow of the water from the can carries with it the air from the bottle. (N. R., 1881, p. 266.)

Lux's aspirator (see Fig. 270) is constructed by fitting two accuratelyperforated rubber stoppers to the ends of a piece of wide glass tubing; four short glass tubes are inserted in the stoppers, as shown in the cut. One of the tubes is for the supply of water, another carries it off, the third tube is connected with the vessel to be exhausted, whilst the fourth tube may be put to the same use, or connected with a vacuum gauge or closed with a stopper. If the air is to be aspirated by one of the lower tubes, the vessel to be exhausted must stand on a higher level than the aspirator. The length of the exit-tube determines the power of the aspirator. It should have a bore of one-fifth of an inch and be at least ten feet long, and it should be provided with a screw pinch-cock to regulate the flow of water. A very simple apparatus is shown in Fig. 271. A very moderate fall of water is needed here. It is, however, adapted only to small operations. Two rather large bottles, of equal capacity, and both provided with nipples near the bottom, are selected. Into the neck of each is fitted a tight-fitting stopper carrying a glass tube bent at a right angle, and the nipples near the bottom are connected with a rubber tube. A Woulfe's bottle having two necks is next selected, and one of the necks fitted with a tight-fitting stopper carrying a small bent tube, to which is attached a rubber tube provided with a conveniently situated pinch-cock. The other end of the bottle is provided with a stopper so perforated that it will receive air-tight a glass funnel. One of the large

FIG. 272.

FIG. 273.

VACUUM.

IN.

bottles is filled with water and placed on an elevated shelf, when the water will flow down to the other bottle and if the connections are w made as shown in the cut, it will aspirate through the funnel; and if the funnel is full of liquid, it will cause the latter to run through quite Vacuum-pump. rapidly. When the lower bottle is full, it is substituted for the upper one, and the connection with the vessel to be exhausted, transferred to it.

Fisher's vacuum-pump.

Water-Pumps acting by Pressure.-It is usually inconvenient to operate aspirators which depend upon a fall of water through a long tube, except in high buildings: hence water-pumps which are operated by pressure are generally preferred in cities and towns, or in localities where water is supplied under pressure. The following are selected