486

Effects of Conical Ajutages,

[Book V. of a tapering form to them, or by enlarging the ends themselves. Of a number of experiments, the following will be sufficient for our present purpose. In two of the tubes (Nos. 211 and 212) the exhausting pipe did not protrude into the blowing one: in No. 213 it did. As it is difficult to keep up a strong blast from the lungs through a pipe so large in the bore as half an inch, No. 211 was made of quarter-inch tubing, and No. 212 of five-sixteenths. The blowing tube of No. 213 was seven-sixteenths, and the exhausting one three-sixteenths, and all were made of lead. Besides the tubes just named we prepared a dozen conical ones, nine inches long, the small ends one-quarter inch bore, and the large ones varying from three-fourths to 2 inches. They were made of tin plate, the seams were lapped, and no particular care was taken in their formation. From numerous trials with them in a variety of ways, we obtained the best results with two, one of which was 14 inches at the large end, and the other seveneighths. But of these the latter, marked C in the cut, generally caused the water to rise highest in the exhausting tube. The discharging end of

No, 211. No. 212, No. 213.

No. 211 extended 1 inches from the joint, and the opposite end 2 inches. When blown through in the direction of the arrow, part of the current descended through the water, but when the conical pipe C was held close to the discharging end the liquid rose in the vertical pipe 9 inches. A quarter of an inch was next cut off the discharging end and C again applied, when the water rose 12 inches. The end was next remered out with the tapered prong of a file, when the water rose (without C) 11 inches. Another portion was next cut off, leaving only half an inch in front of the joint, and the end swelled out as before, upon which the rise was 7 inches; but when C was applied the water rose 17 inches. In all the trials with C it was necessary, in order to obtain the best results, that its axis should coincide with that of the blowing tube; otherwise the current of air is deflected in its passage. The length of the blowing end of the tube should be no more than what is necessary to give a straight direction to the current. If longer than this, the velocity and strength of the blast is unnecessarily diminished by friction against the prolonged sides. The blowing tube should also be straight and smooth within; for the energy of the blast is less diminished in passing through a straight than through a crooked channel-through a smoothly polished tube than through one whose interior is marked with asperities. Moreover, dints or bruises in a pipe produce counter currents, and materially diminish the ascent of the liquid. In small tubes, the end received into the mouth might be enlarged or cut obliquely to facilitate the entrance of the air; for if the fluid be retarded in its entrance, part of the force exerted by the lungs is uselessly expended. It is immaterial in what position the blowing tube is used.

In No. 212 the blowing tube was jointed to the exhausting one at an angle of 200. The part in advance of the joint was 12 inches. Upon trial, the liquid rose seven inches. The tube D was applied, (its small end being enlarged to five-sixteenths) and the water rose nine inches. The tube was then swelled out by the prong of a file until its orifice was seven-sixteenths of an inch, when the rise was 10 inches. D was then applied, its end entering the other, and the water rose 18 inches. Previous to this trial D

Chap. 2.]

When applied to Blowing Tubes.

487

had become slightly bruised in the middle of its length by a fall: the bruises were taken out, and the water rose 24 inches. Various portions were cut from the large end of D, but no diminution of the rise occurred while 3 inches remained, and this length from several trials gave better results than when the tube was made shorter.

In No. 213, the discharging end of the blowing tube was 12 inches long. Without any additional tube, the water rose 16 inches. The end was swelled out, and the liquid rose 19 inches. D was applied, and it rose 29 inches. C was then tried, which made the liquid ascend 31 inches. The discharging end was reduced in length from an inch and a half to half an inch, and the elevation of the liquid was diminished, both with and without the additional tubes C and D.

Two other tubes connected like No. 213 were also tried. From slight variations in the dimensions of the passage way over the end of the exhausting tube, the results varied. Without the additional tube C, one raised the water only seven inches, while with C the rise was 17 inches. The other alone raised the liquid 14 inches, and with C 20 inches.

It has been seen from preceding experiments, that when two tubes of the same bore are united, as in Nos. 203, 204 and 211, part of the current from the mouth will descend the vertical one, if but half an inch or even less of the discharging end project beyond the joint. To ascertain at what distance from the joint this descent of the current could be counteracted by additional tubes, we connected two pieces of leaden pipe (A and B) five-sixteenths of an inch bore to each other, as in the figure. A was 15

d

No. 214.

B

inches long; B four inches, and joined to the other three inches from the blowing end, thus leaving 12 inches in front of the joint. The lower end of B dipped not more than one-tenth of an

inch in water. A tapered pipe, C, whose wide end was 14 inches and the small one five-sixteenths was attached to A, and upon blowing through A, part of the blast descended through B. Small portions were then successively cut off the discharging end of A, until the air ceased to descend in B. When nine inches remained in front of the joint, but a solitary bubble or two escaped through the water, and after another inch was removed, leaving eight inches in front, the whole current from the lungs passed through A. The conical tube was nine inches long, and after the last result it was divided at D, four inches from the end. Upon removing the part thus cut off, air again descended through B.

From this experiment we see that the influence of such terminations as C to cylindrical air tubes, extends to a distance equal to 25 times the tube's diameter. It is however modified by the velocity of the motive current. When high steam is used instead of air, the distance is greatly diminished, and in some cases annihilated. A smoky chimney, or one with a feeble draft, may be cured by enlarging its upper part like the additional tube C in the last figure. The reason why an equal amount of rise in the exhausting tube is not produced by additional ones to such devices as No. 213, arises no doubt from the projection of the exhausting tube into the blowing one, which prevents the blast from sweeping directly into the conical one and filling the latter, a condition necessary to the increased ascent.

Some applications of the principle illustrated by the preceding experiments may be noticed:-1. In siphons for decanting corroding or other liquids-for which see remarks on these instruments in a subsequent

488

Draft of Chimneys- Ventilation of Ships.

[Book V. chapter. 2. Increasing the draft of chimneys, as well as preventing them from smoking. Instead of the old fashioned caps of clay or the moveable

A

No. 215.

ones of iron, let them be made in the form of the annexed figure, and either of sheet iron or copper. A short pipe should be fixed on the chimney, and over it an outer one (shown in the cut) to turn freely, but as close as possible without touching, that the horizontal one to which the latter is attached may veer round with the wind. The vane V keeps the opposite end A to the wind, which enters as indicated by the straight arrow, and in passing through sweeps over the projection and causes a vacuum in the chimney, as in the blowing tubes already described.

A device of this kind might be made to act in windy weather as a perpetual bellows to blast or refining furnaces, and also to those of steamboats and locomotive carriages. When used on chimneys of the latter, a contrivance to turn and keep the blowing tube fore and aft, as the carriage is turned, would be required. The joint where the perpendicular tube moves over the fixed one might also be made air-tight by an amalgam, on the principle of the water lute. From the experiments with the tubes Nos. 206, '7, '8, '9, '10 and '13, it follows that if the waste steam of a locomotive carriage were discharged over the mouth of the chimney as above, instead of up its centre, the resulting vacuum would be greater.

It is worth while to try whether wells, mines, and the holds of ships, could not be more speedily and effectually ventilated by a similar device than by the common wind sails used in the latter. These displace the noxious vapors by mixing fresh air with them, but by the proposed plan the foul air might be drawn up alone, while the atmosphere would cause a steady and copious supply to stream in at every avenue.

If two or three exhausting tubes, of metal or of any other suitable material, (whose diameter for a ship of the largest class need not exceed three or four inches) were permanently secured in a vessel, their lower ends terminating in or communicating with those parts where noxious effluvia chiefly accumulates, and the upper ends leading to any convenient part of the deck, sides or stern, so that the blowing part could readily be slipped tight into or over them, the interior might be almost as well ventilated, even when the hatches were all down, as the apartments of an ordinary dwelling. It appears to us moreover, that a vessel might by this means be always kept charged with fresh and pure air; for the apparatus might be in operation at all times, day and night, acting as a perpetual pump in drawing off the miasmata. The only attention required would be, to secure the blowing tube in its proper position with regard to the wind during storms. In ordinary weather its movements might be regulated by a vane, as in the figure, when it would require no attention whatever. The upper side of the blowing part of the tube should be cut partly away at the end, so as to facilitate the entrance of descending currents of wind. See the above figure.

Chap. 3.]

Vacuum by Currents of Steam.

489

CHAPTER III.

Vacuum by currents of steam-Various modes of applying them in blowing tubes-ExperimentsEffects of conical ajutages-Results of slight changes in the position of vacuum tubes within blowing ones-Double blowing tube-Experiments with it-Raising water by currents of steam-Ventilation of mines-Experimental apparatus for concentrating sirups in vacuo-Drawing air through liquids to promote their evaporation-Remarks on the origin of obtaining a vacuum by currents of steam.

As the utmost rarefaction which can be produced with blowing tubes by the lungs is exceedingly limited, we next endeavored to ascertain how far it could be carried with currents of steam. This fluid presents several advantages. By it a uniform blast can be obtained and kept up, and its intensity can be increased or diminished at pleasure: hence experiments with it can be continued, repeated or varied, till the results can be relied on. As it is inconvenient to measure high degrees of rarefaction by columns of water, mercury was employed for that purpose; and as the blowing tubes &c. if made of lead or block tin would have become soft and bent by the heat, they were all made of copper, while the additional or conical tubes (generally) were of cast brass, and smoothly bored. A detail of all or even half the experiments made would possess no interest to general readers, and would be out of place here; we therefore merely notice such as gave the best results. The force of the highest steam used was equal to a pressure of 90 pounds on the inch. It was measured by the hydrostatic safety-valve described in the Journal of the Franklin Institute, vol. x 2d series, page 2.

While engaged in the prosecution of this subject, we supposed that currents of steam had never been employed to produce a vacuum; but it will be seen towards the close of the chapter, that we were anticipated by a French gentleman, though to what extent we are yet uninformed. We were not aware of the fact until all the following experiments had been matured, and most of them repeatedly performed. The circumstance affords another example of those coincidences of mental and mechanical effort and resource with which the history of the arts is and always will be crowded. The shoemakers' awl was formerly straight, but is now bent: the author of the improvement was supposed to have lived in comparatively modern times; but recent researches among the monuments of Egypt have proved, that the artists who made shoes and wrought in leather under the Pharaohs used awls identical in shape with the modern ones.

The expenditure of high steam through open blowing tubes like those figured in Nos. 203 and 204 would obviously be enormous, since there is nothing in them to prevent its passing freely through. They are not therefore so well calculated for practical operations as those in which the end of the exhausting pipe projects into the blowing one and contracts the passage for the vapor, as in Nos. 205-210. These are also better on another account-they produce a better vacuum. Economy in the employment of steam is of the first importance; hence it was desirable to determine if possible that particular construction of the apparatus by which the highest degree of rarefaction may be obtained with the least expenditure of vapor. Fortunately for the solution of this problem, there is one form of the apparatus in which both are eminently combined; for while

490

Apparatus for employing Currents of Steam.

[Book V. an increase of the steam's elasticity increased the vacuum, an increased discharge of the vapor was often found to diminish it. This was frequently the case when high steam was employed: for example, if the cock through which steam passed into the blowing tube marked C in No. 217 was wide open, the mercury would sometimes fall two or three inches, but when partially closed, would instantly rise; thus indicating that it is the velocity and not the volume of vapor passing over the orifice of the exhausting pipe, upon which the vacuum depends.

We first passed steam through tubes connected like No. 213, both with and without the conical ajutages C D in Nos. 211 and 212. Various proportions of the steam passage over the orifices of the vacuum or exhausting pipes were also employed, as at A, B, C, D, E, No. 216, which represent horizontal sections of the vacuum pipe and steam passage over its orifice. The dark parts show the passage for the steam, and the inner circle the mouth of the vacuum tube. In A the steam channel did not extend over one-fourth of the circumference of the orifice; in B it reached nearly half way round; in C three-fourths; while in D and E it extended entirely round. Upon trial, the vacuum produced by B was greater than that by A; C surpassed B, and D uniformly exceeded them all. We therefore finally arranged the apparatus as shown at No. 217, in which A is a brass tube composed of two conical frustums united at their lesser ends. The longer part, A, was smoothly bored and polished in the direction of its length, to remove any minute ridges left by the borer. The interior diameter of the large end was an inch and an eighth, and of the smallest part nineteen-fortieths, (rather less than half an inch.) The external diameter of the vacuum pipe B was seventeen-fortieths, so that the annular space left round it for the steam was only one-fortieth of an inch in width, being about as small a space as could well be formed without the pipe B touching A. The length of A from the contracted part was 52 inches. A glass tube three feet long, whose lower end was placed in