Chapter 6

By pulling out one of the buttons of the wind chest, we admit the air through eleven holes at a time, having an angular distance of 30° and directing it against the corresponding circle of holes on the turning disk. If the arrangement of holes is not repeated identically twelve times on the same circle, we cannot, of course, make use of the above arrangements of holes of the wind tube, and we must then employ one of the movable brass tubes, which communicate with the interior of the wind chest by means of rubber tubes and stopcocks. The experiment with disk 1, circle 4, for example, requires the use of one of these two tubes, while the perforated wind tube of the wind chest may be used with all the other circles of the same disk.

B.

If t is much less than t', while t' is a multiple of t, the note (t+t')/2 disappears, and the notes t+t' and t are heard.

Disk No. 2 has--

On circle No. 1 12 holes, distances 30° " " 2 36 " " 10° " " 3 48 " " 7½° " " 4 60 " " 6° " " 5 24 " " t= 5°, t'=25° " " 6 24 " 6° 24° " " 7 24 " 7½° 22½° " " 8 24 " 10° 20°

Circle 8 produces the notes of circles 1 and 2; circle 7, those of 1 and 3; circle 6, those of 1 and 4; and circle 5, the note of circle 1 and of its sixth harmonic.

C.

If the same circular arc is divided into m and n equal parts; that is to say, if mt=nt', we obtain the notes m and n.

Disk No. 3 has--

Distances. On circle No. 1 24 holes, distances 15° " " 2 24 " " 15° & 27 holes, 13-1/3° " " 3 24 " " 15° " 30 " 12° " " 4 24 " " 15° " 32 " 11-1/4° " " 5 24 " " 15° " 36 " 10° " " 6 24 " " 15° " 40 " 9° " " 7 24 " " 15° " 45 " 8° " " 8 24 " " 15° " 30, 36, & 48 holes

Circle 1 produces a single note, circle 2 a second, circle 3 a third, circle 4 a fourth, 5 a fifth, 6 a sixth, 7 a seventh, and 8 a perfect chord.

II.

_Experiments to prove that the shocks may proceed from two or several different places to conspire in the formation of a note, provided that the isochronism of the shocks is sufficiently exact, and that the shocks are produced in the same direction_.

Disk No. 4 has--

On circle 1 24 holes. " " 2 36 " " " 3 23 " " " 4 12 at an angular distance of 10° from the holes of circle 3. " " 5 12 holes at an ang. dist. of 20° from those of circle 3 " " 6 12 " " " 0° " " " 7 12 " " " 15° " " " 8 12 " " " 15° "

1. If from the same side two currents of air at an angular distance of 15° are directed against circle No. 8 of 12 holes, we obtain the octave of the note produced by the same circle if only one current is used.

The wind-chest is provided with a special arrangement for this experiment. By pulling out button 8, we give vent to 12 currents of air spaced like the twelve holes of the disk; on pulling out button 9 we also produce 12 currents, but they are situated just between the first. Each of these two buttons pulled out alone will produce the same note corresponding to 12 holes, but drawn together they produce the octave, or the note of circle 1.

2. If two currents of air are directed against two similar circles whose holes are situated on the same radii, we obtain the same result.

In this experiment, circles 7 and 8 are sounded by pulling out buttons 7 and 9.

3. When two currents of air are directed on the same radius against two circles of similar holes arranged alternately, these circles sounded simultaneously will produce the octave of the note which one of them would give alone.

This experiment is performed by sounding circles 6 and 7 and pulling out buttons 6 and 7.

4. If we direct three currents of air on the same radius against three similar circles having holes alternating by a third of the distance between two holes of the same circle, the three circles together produce the fifth of the octave (Note 3) of a single circle.

Circles 3, 4, and 5 sounded together emit the note of circle 2.

(By sounding only two circles, 3 and 4, or 4 and 5, we make the same experiment with two circles as disk No. 2 enabled us to make with circle 8 alone; also, by sounding circle 3 alone, we obtain the note corresponding to 12 holes; then pulling out button 4, the notes corresponding to 12 and 36 holes are heard suddenly and very strongly; but as soon as circle 5 is sounded also, the note of 12 disappears completely, and we have left only that corresponding to 36 holes.)

III.

_Effects of interference produced by shocks in opposite directions_.

1. If we direct against a circle of holes two currents of air in opposite directions, the note obtained with a single current is very much weakened, if the two currents reach the holes simultaneously. If the impulses are not isochronous, the intensity of the note is increased.

2. If the two currents are directed against two circles of the same number of holes, the effect is the same as for the two preceding cases.

3. If two currents of air are directed against two circles, one of which has twice as many holes as the other, we obtain only the low note if every shock of one is isochronous with every shock of the other.

We obtain the notes of both circles, one of which is the octave of the other, if there is no isochronism between the shocks.

Disk No. 5 has three circles of 36, 36, and 72 holes. The air currents are directed against the circles of holes through the movable tubes, made so that they can be detached at pleasure. All these experiments require great precision in the arrangement of these wind tubes. To make sure that the tubes are simultaneously before two holes of the disk, it is well to put little rods through the holes, reaching into the wind tubes, and to remove them only when the tubes are firmly attached. The experimenter should be careful also to place the two tubes exactly at the same distance from the turning disk. It is clear that notwithstanding all these precautions we never obtain perfect interference, but only the weakening of notes that ought to disappear entirely if all the arrangements were made with mathematical exactness, and also if the ear could have absolutely the same position with regard to impulses produced in opposite directions.

IV.

_Beats_.

Disk No. 6 has--

8 circles of holes to the number of 1, 2, 23, 24, 25, 47, 48, 49.

Circles 3 and 4, 4 and 5, 6 and 7, and 7 and 8 ought to produce as many beats as circle 1 produces simple shocks; and circles 3 and 5, 6 and 8, as many beats as circle 2 produces simple shocks; but we must content ourselves in these experiments with a much less perfect result, for the following reasons: The disk never being rigorously plane, alternately approaches the single wind pipe and recedes from it. No matter how slight this deviation is, every sound given by a single circle is heard with periodical intensities which complicate the phenomenon. This inconvenience could be avoided by placing several wind-pipes around the circle; but while we can extend the period of the holes in two circles (whose difference is 1) around the whole circle by blowing through a single wind tube, we would be compelled to limit it to the distance between two wind tubes, and it would become too short; for, when the disk rotates with a velocity sufficient to produce notes high enough and intense enough, the beats become too numerous to be easily perceived.

Besides these provisions, which sufficiently illustrate the points to which we desire to call especial attention, Koenig also furnishes two more disks.

The seventh contains 8 circles having 48, 54, 60, 64, 72, 80, 90, and 96 holes respectively. The 1st, 3d, 5th, and 8th will produce a perfect chord when the air is admitted through the 11 holes in the wind chest; with one wind tube the entire gamut may be obtained.

Finally the eighth disk contains 8 circles of holes, whose numbers are in the ratio of 1:2:3:4, etc., and which may be used to illustrate harmonics. C. F. K.

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THE MOTIONS OF CAMPHOR UPON THE SURFACE OF WATER.

[Footnote: Continued from SUPPLEMENT No. 391, page 6240.]

To have these movements occur in a constant and invariable manner upon the surface of water, and especially upon mercury, it is necessary to take precautions in regard to cleanliness, this being something that we have purposely neglected to mention to our readers. For we wished, through this voluntary omission, to stimulate their sagacity by bringing them face to face with difficulties that they will perhaps have succeeded in overcoming, with causes of error that they will have perceived, and the principal one of which is the want of absolute cleanliness in the water, vessels, and instruments that they may have used for the experiments.

Thus, very probably, they will have more than once seen the camphor remain immovable when placed in vessels in which they had hoped to be able to see it undergo its gyratory and other motions. Their astonishment will have been no less than our own was when we noticed the sudden cessation of the camphor's motions under the influence of vitreous or metallic objects, such as glass rods or tubes, pieces of gold, silver, or copper coin, table knives, etc., dipped into the liquid in which such motions were taking place before the immersion of the objects under consideration.

The instantaneously _sedative_ power of the human fingers, or of a hair, will have, perhaps, reminded them of some sort of sorcery, or of some diabolic art worthy of the great Albert.

As for ourself, we confess that, after repeating the curious experiments of Mr. Dutrochet day after day, and scrupulously following his directions, we have, in the presence of our results, that were exactly identical with his, almost been tempted to believe ourself to be the victim of some occult power, or at least of some optical illusion, the true cause of which remained a mystery to us. Finally, after many fruitless attempts to find a key to the enigma that engaged our attention, the light finally dawned upon us, and then shone straight in our eyes.

In comparing the last results of our experiments with those that we had obtained previously, we saw, for example, that the camphor moved in the test glasses at a level that was notably higher than that at which its gyration took place the day before, or the day before that. And yet we had always used the same vessels, the same water, and particles detached from the same lump of camphor.

To what, then, could be due the difference observed between the two levels at which we had, in the first and last place, seen the camphor execute its movements? In the absence of any answer that was satisfactory, we finally suspected that the difference that we had noticed was ascribable to the fact that, after the numerous washings that the apparatus had been submitted to in having water poured into them to repeat the experiments, they had gradually been freed from impurities of whatever nature they might have been, and which, unbeknown to us, might have soiled their sides.

Starting with this idea, which was as yet a hyphothetical one, we began to wash our hands, glasses, etc., at first with very dilute sulphuric acid, and then with ammonia. Afterward we rinsed them with quantities of water and dried them carefully with white linen rags that had been used for no other purpose; and finally we plunged them again into very clean water. We thus cut the Gordian knot, and were on the right track.

In fact, on again repeating Mr. Dutrochet's experiments, with that minute care as to cleanliness that we had observed to be absolutely necessary, we saw crumble away, one after another, all the pieces of the scaffolding that this master had with so much trouble built up. The camphor moved in all our vessels, of glass or metal, and of every form, at all heights. The immersed bodies, such as glass tubes, table knives, pieces of money, etc., had lost their pretended "sedative effect" on a pretended "activity of the water," and on the vessels that contained it. The so-called phenomenon of habit "transported from physiology into physics," no longer existed.

The likening of the apparatus employed to obtain motions of camphor upon water, with the entirely physiological apparatus by means of which nature effects a circulation of the liquid contained in the internodes of _Chara vulgaris_, had proved a grave error that was to be erased from the science into which it had been introduced by its author with entire good faith. The true cause of _life_ had not then been unveiled, and the new agent designated as _diluo-electricity_ vanished before the very simple and authentic fact that camphor moves rapidly upon the surface of very pure mercury, in which no one would assuredly suppose that that volatile substance could dissolve.

Mr. Dutrochet attaches great importance to the manner in which the water is poured (with or without agitation) into the vessel with which the experiment is performed. The matter is in fact of little or no importance, and to prove this, it is only necessary to employ a test glass (see figure) provided with a lateral tube, A, that terminates in a lower tubulure, B, above which there is a contraction, C. Upon pouring water into the lateral tube until the level reaches D, and placing a particle of camphor on its surface, the camphor will be seen to continually move about, even when the liquid has reached the upper edge of the vessel. To reduce the level to various heights, it is only necessary to revolve the tube in the cork through which it is fitted to the tubulure. In proceeding thus, agitation or _collision_ of the water is avoided; and yet if the test glass is very clean, the camphor will continue to move at every level of the water.

But, some one will doubtless say, how do you explain the stoppage in the motions of the camphor on the surface of water contained in vessels that are not perfectly clean? Before answering this question, let us say in the first place that the cause of the motions under consideration is due to nothing else but the evaporation of this concrete oil--to effluvia that escape from all parts and that exert upon the body whence they emanate a recoiling action exactly like that which manifests itself in an ælopile mounted upon a brasier, or, better yet, in the explosion of a sky-rocket. A portion of these camphory vapors, as well as a small portion of the camphor itself, dissolves in the water and forms upon its surface an oily layer which is at first very slight, but the thickness of which may increase in time until it becomes (especially if the vessel is narrow) a mechanical obstacle to the gyration of the small fragments of camphor that it imprisons, and whose evaporation it prevents. Now, as this layer of volatile oil may and does evaporate, in fact, after a certain length of time, the camphor then resumes its gyratory motions; but there is not the least reason in the world for saying on that account that it "has _habituated_ itself to the cause which had at first influenced it, and that, too, in modifying itself in such a way as to render null the influence of a cause that has not ceased to be present" (Dutrochet, _l.c._., p. 50).

We have been enabled to convince ourself of the existence of this oily layer of camphor when it was of a certain thickness by introducing under the water on which it, had formed, a few drops of sulphuric ether whose sudden evaporation produced sufficient cold to instantaneously congeal the layer in question and thus render it perfectly visible to the eye. The slight layer of greasy matter that habitually lines the sides of vessels from whence no effort has been made to remove it, produces effects exactly like those of the oil of camphor, that is to say, that in measure as it becomes thicker it likewise arrests the motions of the concrete volatile essence.

This is precisely what happens in a test-glass in which we see the camphor in motion become immovable if the level of the water be raised a few centimeters, and, more especially, if it be raised to the upper edge of the apparatus. In its slow ascent the liquid _licks_ up, so to speak, the oily layer that lines the inner surface of the vessel, and this material spreads over the surface of the water and forms thereupon a layer which, in spreading over the bit of camphor itself, prevents its evaporation, and, consequently, its motions. The existence of the layer under consideration cannot be doubted, since it is made to disappear by causing the water to-overflow from the edges of the vessel, and, more easily still, by spreading a piece of filtering paper over the liquid in which the camphor is in a state of rest. As soon as the paper is removed (without the water being touched by the fingers, it should be understood), the camphor resumes its motions and afterward continues them at all levels.

The fingers themselves, provided they are very clean, have no power to stop the gyration. The following experiment, which is easy to repeat, is an unquestionable proof of this.

Wash carefully the middle finger with aqua ammonia, and afterward with plenty of water, and then dip it into a drinking glass in which a fragment of camphor is rapidly moving, and the gyration will not be stopped. But it will be made to stop instantly if the finger in its natural state (that is, covered with the fatty substances that ordinarily soil the fingers, especially in summer) be dipped into this same glass.

_Movements of Camphor upon Mercury_.--In order to study the motions of camphor, mercury possesses, as compared with water, a great advantage, and that is that we can easily assure ourselves of the degree of cleanliness of this metal by means of the condensed breath. The vapory-deposits thereon in a uniform manner if the mercury is perfectly clean, but forms variously shaded and more persistent spots if it is soiled by foreign bodies But it is extremely difficult to clean mercury completely. To do so Mr. Boisgiraud and I take distilled mercury and leave it for a long time in contact with concentrated sulphuric acid, taking care to often shake the mixture. Then, after removing the greater part of the acid, we throw the metal into a vessel containing quick lime in powder, and finally pass it through a filter containing a few holes in its lower part.

Purified by this process, mercury not only permits of the motions of camphor on its surface, but renders visible the traces of the vapors that escape from it, and which resemble small tadpoles with a long tail that are endowed with very great agility. Nothing is more curious than to see the particle of camphor successively ascend and descend the strongly pronounced curves presented by the mercury near the sides of the vessel that contains it. On raising the temperature of the metal slightly, the motions of the camphor on its surface are accelerated, and the same effects occur with water that has been slightly heated.

The experiments that we have just called attention to show what importance slight impurities may have upon certain results. "They prove," says our learned colleague Mr. Daquin, "that there exists upon polished substances an imperceptible coating of those fatty matters which serve to-day to explain Moser's images." We find therein also a manifest proof and a rational explanation of those grave errors into which the presence of these fatty matters, that have hitherto been scarcely suspected, led so clever and so distinguished a scientist as the illustrious discoverer of endosmosis.--_N. Joly, in La Nature_.

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CARBONIC ACID IN BEER.

We present a diagram, on exposition at the last Brewers' Convention in Detroit, of the racking device, devised by J. E. Siebel in 1872, and used at that time in the brewery of Messrs. Bartholomae & Roesing, in Chicago. The object of the apparatus is to retain as much carbonic acid in the beer as possible while racking the same off into smaller packages from the storage vats. The importance of this measure is apparent to every one who knows what pains are taken to preserve the presence of this constituent in all the former stages of the brewing process. In the method of racking off which is in present use in most breweries, the beer is forced through a rubber hose from the cask in the store vault to the barrels, kegs, and smaller packages in the fill room. Owing to the excess of pressure in the beer as it enters the keg, it is evident that a large amount of the carbonic acid gas must escape. The escape of carbonic acid during the process of racking off is indeed so large that even a small difference in the pressure of the atmosphere causes a remarkable difference in this respect. It is, therefore, evident that if a larger pressure can be maintained while racking off, a larger amount of carbonic acid gas will remain in the beer. It is true that the racking off will take a little longer time if done under pressure, but this inconvenience is certainly insignificantly small, when compared with the other labors and troubles daily undergone in a brewery, for the sole purpose to preserve in the beer the carbonic acid in that form in which it has been formed during the fermentation, and in which form it has far more refreshing and other valuable properties than in any other form in which it may be subsequently introduced into the beer by artificial means. The apparatus designed in the accompanying cut is calculated to artificially produce a higher pressure of the atmosphere, at least within the keg which is to be filled with beer. For this purpose, the beer from the store cask running through the pipe, B, enters the keg through a hollow copper bung, fitting light into the bung hole by means of a rubber washer. The air contained in the keg, being replaced by the beer, is forced out by means of the hollow copper bung, taking its course through the pipe, inscribed "Glass Gauge," until it is allowed to escape in the standpipe, C, containing a column of water, the height of which designates the pressure within the keg, and a consequently increased retention of carbonic acid gas. If the keg or barrel is filled with beer, the same becomes apparent from the beer showing itself in the glass gauge; then the faucet, B, is closed, the copper bung is lifted out of the bung hole, and the beer contained in the pipe is just sufficient to completely fill the keg, which is then bunged up, while the apparatus is transferred to the next keg. Should the attendant carelessly neglect to close the faucet in proper time, the surplus beer will not necessarily be wasted, but will be collected in the vessel, D, whence it can be drawn off through e.--_Chemical Review_.

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ON THE DIFFERENT MODIFICATIONS OF SILVER BROMIDE AND SILVER CHLORIDE.