Chap. 3.]

Apparatus for evaporating liquids in vacuo.

495

might be beneficially applied to large blowing tubes, and thus contribute to the same result.

There are other useful applications of these blowing instruments. One of our first attempts was to employ them as substitutes for the expensive air-pumps worked by steam-engines, employed in evaporating sirups and refining sugar by Howard's vacuum plan.

No. 221. Apparatus for evaporating liquids in vacuo.

We fitted up a very strong old still, (No. 221) three feet in diameter and about the same in depth. A jacket of copper was fitted to its lower part so as to form a double bottom. The discharging pipe passed through the jacket, and was closed by a valve V. Steam being conveyed into the jacket heated the liquid within the still, but instead of taking steam from the boiler expressly for this purpose, we made use of that by which the vacuum was produced. The open end of a blowing tube was inserted into the jacket as represented in the cut, and the vacuum tube B connected by a cock to the neck of the still. C the steam cock and pipe leading to the boiler. Da pipe that conveyed the surplus steam from the jacket into the chimney. The orifice of the vacuum pipe within the blowing one was three-eighths of an inch diameter, and the annular space around it for the passage of the steam was the same as in No. 217. At the first trial with this apparatus, 25 gallons of sirup were put into the still through the funnel, and the cock shut. The steam cock C was then opened, and in a few moments the mercury in the gauge rose 15 inches, but in eight minutes fell to 10 inches, the fall being occasioned by the evolution of vapor in the still. The steam in the boiler was raised higher, until the mercury rose to 16 inches; but after the operation had been continued about half an hour it commenced rising, and was at 18 inches when the experiment was closed. On another trial 32 gallons of sirup were poured in, and when C was opened the mercury rose to 22 inches, but in ten minutes fell to 17. In half an hour it began slowly to rise, and in fifteen minutes reached to 20 inches, at which height it remained when the concentrated sirup was withdrawn.

Had a double tube like No. 220 been used, the vacuum might probably have been carried to 28 or 29 inches, and the operation performed in much less time. The experiment however shows how small a tube can with

496

Origin of obtaining a Vacuum by Currents of Steam. [Book V.

draw the vapor arising from a surface of seven square feet. It would be an advantage to apply two or perhaps three separate blowing tubes, of different sizes, to each sugar pan-using the largest first, to draw off the the bulk of the vapor, and finishing with the smaller ones. There would be a saving of steam, and the vacuum might be carried higher towards the close of an operation with a very small tube and current.

Another mode of using these tubes to promote evaporation, is to draw air through liquids instead of forcing it through them with pumps, as in the pneumatic processes of concentrating sirups. An open boiler, four feet in diameter, was inverted and placed in another over a fire and containing sirup a blowing tube, the orifice of whose vacuum pipe was three-fourths of an inch diameter, was connected to the inverted vessel, and it drew so much air under the edges as to cool the liquid to such a degree that the operation of concentration was prolonged to twice the ordinary time.

While engaged in making the experiments described in this chapter, (in 1835) and stimulated by the conviction that we were the first thus to apply currents of steam for the purposes of raising water and promoting the evaporation of liquids at low temperatures, &c. we were exceedingly surprised to learn that something of the kind had been previously done, or proposed to be done, in France. As we had made preparations to secure the invention by a patent here, and by others in Europe, our experiments were discontinued with a view to ascertain the particulars of the French plan, that it might be known whether we were traveling on beaten ground or not; but to the present time we have not obtained any specific description of it, nor do we know whether it consisted of a jet of steam discharged through the centre of a tube, as in Nos. 208, 210, and as applied to increase the draft of chimneys in locomotive carriages, or whether the jet was directed over the outside of a part or the whole of the end of the vacuum tube-nor have we learnt what degree of rarefaction was obtained. We have therefore concluded to insert the preceding notice of our labors, that since we cannot claim priority in the research, we may be allowed the credit, if any be due, for our modes of application, and the extent to which they carried the vacuum and are obviously capable of carrying it, especially by such devices as No. 220.

The whole of the devices, from the blowing tubes described in the last chapter to the apparatus for boiling sugar in vacuo described in this, with the exception of the patented plan of raising water by a series of vessels on different levels, originated entirely with ourselves, nor were we indebted either directly or remotely for so much as a hint in maturing them to any persons or writings whatever; and upon them we have also spent no inconsiderable amount both of time and money. But as we have on several occasions shown that new devices, so called, are often old ones, it is but just that we should mete to ourselves the same measure which we have given to others. We therefore with pleasure record the fact, that at a meeting of the Paris Academy of Arts and Sciences, held in January, 1833, M. Pellatans read a paper on the dynamic effects of a jet of steam, of which a notice (not a description of the plan) was published in an English journal, and copied into the Journal of the Franklin Institute for March of the same year-vol. x, 2d series, p. 195.

There is also described in the London Mechanics' Magazine, vol. iii, p. 275, an experiment of a current of air from a bellows directed over the orifice of an inverted glass funnel, which was placed in a saucer filled with water. From this (which we did not see till recently) the blowing tubes described in the last chapter might, with a little ingenuity, have been deduced.

Chap. 4.]

Spouting Tubes.

497

CHAPTER IV.

Spouting tubes-Water easily disturbed-Force economically transmitted by the oscillation of liquids -Experiments on the ascent of water in differently shaped tubes-Application of one form to siphons Movement given to spouting tubes-These produce a jet both by their ascent and descent-Experiments with plain conical tubes-Spouting tubes with air pipes attached-Experiments with various sized tubes -Observations respecting their movements-Advantages arising from inertia-Modes of communicating motion to spouting tubes-Purposes for which they are applicable-The Souffleur.

There is a simple mode of raising water which to our knowledge has never been adopted, nor yet suggested-viz. by straight and open pipes, or, as they might be named, spouting tubes.

Water is raised in the ram (No. 168) by the force which the liquid acquires in flowing through descending channels, but in the instruments to which we now refer, the same effect is produced by its momentum in passing up vertical ones. So far as respects the force of a liquid in motion, it makes little difference in what direction it moves-whether the liquid rise perpendicularly, or having first descended at one angle it ascend at another. A jet d'eau, deducting all resistances, rises with the velocity with which it would fall through the same space; but in practice, the velocity is diminished by the length, figure and dimensions of the channel through which the liquid flows, and of the ajutage from which it escapes. Every person's experience teaches him, that a very small force is sufficient to disturb a large body of water, and that the consequent movement of the liquid is long continued after the force is withdrawn. A stone dropt into a tank, or thrown into a pond, causes waves to rise and roll to and fro over their whole surfaces, and some time elapses ere the movements cease. Days and even weeks elapse after a storm is over before the ocean recovers its previous repose. This effect is the result of the great mobility of water; its particles move with such extreme facility among themselves, and so actively impart their motion to each other, that a force once communicated to them is long ere it becomes exhausted. It is the same to a certain extent when waves rise and fall within tubes; for although the friction of liquids against the sides of these channels is considerable, especially in small ones, still the force in the central parts is but slowly consumed. A device therefore by which the oscillation of liquids is employed in transmitting forces, will probably consume as little in the transit as any mechanical device known.

It has already been remarked, that the momentum of a flowing liquid suffers less in passing through a short than through a long tube-through a straight than a crooked one; and we may add that this is more especially true when the figure of the tube is expressly designed to facilitate the passage of the moving liquid, instead of being uniform in its bore throughout. Now in these particulars spouting tubes are eminently superior to others, or they may be made so. They are short, straight, and of a form adapted to the rising wave within them.

Motion is imparted to water in a spouting tube either by depressing the liquid below the orifice and then admitting it to enter, or by excluding it from the tube till the lower orifice of the latter be sufficiently immersed. If a pipe whose lower end is closed be plunged perpendicularly in water,

498

Experiments with Spouting or Open Tubes.

[Book V. the liquid will rise within it the moment its end is opened; but it will depend upon the length and figure of the tube, and the relative proportion of its two orifices, whether the liquid rush up above the surface without, or slowly reach it and there remain.

The following are selected from a number of experiments made several years ago. Instead of closing the lower orifice, the upper one was closed with the fore finger, the confined air acting the part of a cork, and preventing the liquid from entering until the finger was removed.

EXPER. I.-No. 222, a cylindrical glass tube, 18 inches long and half-inch bore. Its upper orifice was closed air-tight by the finger, and the lower one then held four inches under the surface of the water in the vessel. Upon raising the finger, the liquid rose in the tube six inches; i. e. its momentum carried two inches higher than the surface in the cistern, and after a few oscillations it settled at the same level. Cylindrical tubes of various sizes were tried at different depths, and the average extent of the rise (above the surface) was equal to half the length of the part of the tube immersed below the surface. If No. 222 dipped four inches, the rise was two-if eight inches, it was four-and if twelve, it was six. By contracting either orifice the effect was diminished.

EXPER. II.-No. 223, a tube slightly conical, 16 inches long, the diameter or bore of the large end half an inch, and that of the small end onethird of an inch. The rise of the liquid in this exceeded that in No. 222. When tried with the large end up, little or no rise took place.

EXPER. III.-No. 224, another tube, 18 inches in length, the diameter of whose upper orifice was three-sixteenths and of the lower seven-eighths of an inch. Four and a half inches of the lower part was cylindrical. When dipped four inches in water and the finger removed, the liquid rose but two inches above the surface. This was owing to the cylindrical form of the lower part of the tube, all the water that entered being required to fill the lower part. When the dip was six inches, the rise was five; when eight, the jet passed out of the tube and ascended sixteen inches. When the tube was lowered to ten inches below the surface, the jet rose thirty inches; and when the end of the tube was twelve inches under the surface, the jet ascended four feet and a half. Fourteen inches dip threw it six

Chap. 4.]

Experiments with Spouting or Open Tubes.

499

feet, and sixteen inches dip caused it to ascend over seven feet. The rise in cylindrical tubes, we have seen, bore the same relation to the dip at various depths; but this experiment shows that the elevation of the jet in conical tubes increases in a much greater ratio.

EXPER. IV. To include the extreme proportions between the two orifices, we next took a matrass or bolt head (No. 225) and cut a portion from the globe opposite the junction of the neck or pipe. The opening thus made was 34 inches, and the orifice of the tube three-tenths. When the lower end was thrust two inches below the surface, scarcely any rise took place upon removing the finger; and when half the length of the whole was immersed, say ten inches, the rise did not exceed six or seven. The reason was plain: the large volume of air contained in the lower part could not be expelled instantaneously by the pressure of the liquid column. through the small orifice above, but the force of the ascending liquid was consumed in doing this. Various portions were now cut from the lower part, with a view to ascertain the greatest rise that could be obtained with a dip of four inches. This occurred when the diameter of the lower end was reduced to 12 inches: the liquid then rose between nine and ten inches above the surface. The upper end was now heated in the flame of a lamp, and the bore enlarged by pressing into it a tapered piece of wood, till the end resembled the conical ajutage C D in No. 201. caused the liquid to rise an inch higher.

This

EXPER. V. A number of conical tubes of the same length, (21 inches) whose wide ends diverged or flared differently, were next procured, with the view of selecting those through which the jet rose the highest, as affording an approximation to the best form. The one represented at No. 226 gave a better result than any other. With a dip of four inches the jet rose thirteen. The diameter of its lower 'orifice was 1.6 inches, and that of the upper one .4: three inches below the latter, the bore was .2. At seven inches from the small end, the bore was .3-at fourteen inches, .4-and at seventeen inches, .5. The curve given to the flaring part of the lower end should be that which the fluid itself assumes in entering; but that given in the figure is sufficient for all practical purposes to which small instruments of this kind are applicable.

Before proceeding we may observe, that these instruments, simple as they are, and even when charged in the manner indicated above, are susceptible of some useful applications; among which may be named siphons. If the tube No. 226 were bent in the form of one, it might be applied in numerous cases to transfer acids or other liquids; and as it would be charged by the mere act of inserting its short leg into the liquid to be withdrawn, there could be no danger from sucking, &c. as in using the ordinary instrument. It will moreover be perceived from the third experiment, that the extent to which these siphons are applicable increases with the depth to which the short leg can be immersed: but as this chapter is appropriated to the application of spouting tubes to raise water from one level and discharge it at a higher one, their employment as siphons will be illustrated in a subsequent part of this volume.

It will at once occur to every machinist, that to render these tubes of any practical value for raising water, some mode of working them very different from that of alternately opening and closing the upper orifice with the finger, and raising them wholly out of and then plunging them into the liquid, would be required: a mode of regularly and rapidly depressing the liquid within them, that the wave formed by its ascent might rise and fall uniformly.

There is a simple way of doing this:-If the whole of the tube No. 227