« ΠροηγούμενηΣυνέχεια »
eighteen holes, and that the plate B is pierced with only one blast for wind instruments, such as the siren and the organ. hole, and we shall consider the case where the latter coincides Under the feet of a wooden table, fig. 134, is placed a bellows, with one of the upper holes. When the wind from the bellowsc, which is put in motion by a pedal or foot-board, p. A strikes the sides of this upper hole, the moveable disk begins reservoir, D, made of flexible leather or skin, is employed to to revolve, and the space between two consecutive holes collect the air thrown into it by the bellows. If this reservoir covers the lower hole. But as the disk continues to revolve be compressed by weights placed above it, or by means of a in consequence of its acquired velocity, two holes again face rod, T, noved by the hand, the air is forced by a pipe, e, into each other; whence a new impulse is given, and so on. Thus, during a complete revolution of the disk, the lower hole is
Fig. 134, eighteen times open and eighteen times shut; whence arises a series of blasts and stops which puts the air into vibration, and produces a sound when the successive impulses are very
F rapid. If we now suppose that the fixed plate B has eighteen holes, when the disk revolves each hole will produce at once the same effect as a single hole; the sound will, therefore, be eighteen times more intense, but the number of vibrations will not be increased.
In order to find the number of vibrations corresponding to the sound which the apparatus gives during its motion of rotation, we must know how many revolutions the disk makes in a second. This is effected in the following manner :-on the rod r is placed an endless screw, which transmits its motion to a wheel of 100 teeth. This wheel, which advances one tooth at every revolution of the disk, carries on it a pin, P; and this pin causes a second wheel to advance one tooth at every revolution, as seen to the left in fig. 132, No. 1. The axes of these wheels carry two indexes or hands, which move round the dials shown in fig. 131. One of these indexes shows the number laundreds of these revolutions. Two knobs, c and D, are used
P to engage or disengage at pleasure the small wheel and the endless screw. As the sound rises in proportion as the velocity of the disk increases, a determinate sound may be obtained by increasing the force of the wind from the bellows. By keeping up the same current of air during a certain time, say two minutes, we can then read on the dials the number of revolutions which have been made by the disk. Next, by multiplying this number by 18, and dividing the product by the number of seconds, the quotient will give the number of vibrations per second. Fig. 132, No. 2, shows some of the
a box fixed on the table. This box is pierced with holes, toFig. 132, No.2.
which are fitted small metal valves, which can be opened at pleasure by pressing on stops or keys placed in front of the box. On these holes are placed the box of the siren or the
pipes of the organ, F. t
Limits of Perceptible Sound.–Before the experimental researches of M. Savart, philosophers believed that the ear ceased to perceive sound when the number of simple vibrations per second was below thirty-two for low sounds, and above 18,000 for high sounds. But this experimenter has shown that these limits were too contracted, and that the faculty of perceiving, more or less easily, low sounds and high sounds depends more on intensity than height; so that when the extreme sounds are not heard, it is because that these
sounds are not produced with sufficient intensity to make an: 上 t
impression on the organ of hearing. By increasing the diameter of his toothed wheel, and consequently the amplitude and intensity of the vibrations, M. Savart has extended the limit of high sounds to 48,000 simple vibrations per second. For low sounds he substituted for his toothed wheel a bar of iron of about 26 inches in length, revolving between two thin slips of wood distant from the bar only about one-thirteenth
part of an inch. At every passage it produced only a dry parts of the siren more distinctly, and it is added here on this sound, arising from the displacement of the air. When
ce is the cylindricai box, communicating, at the the motion was accelerated, the sound became continuous, bottom, with a tube through which any fluid, liquid or extremely full and deafening. Savart, by the aid of this gaseous, is made to flow for the production of sound; tttt apparatus, found that when it produced from fourteen to sixthe metallic frame-work in which the apparatus is contained ; teen simple vibrations per second, the ear still recognised a
the rod or vertical axis which revolves on itself; 99 the sound well determined, but extremely low. moveable circular disk, placed as near as possible to the fixed Whatever may be the method employed to count the numcircular plate without touching it; and il the toothed wheels ber of vibrations, the results obtained are sufficiently concor-which indicate the number of vibrations,
dant to admit of our considering them as the expression of the The siren, with equal velocity, gives the same sound in truth by a very close approximation. In the middle portion of water as in air; the same sound also takes place in all gases, the scale of sounds, one has been particularly selected as a a fact which shows that a determinate sound depends only on starting point. This selection is entirely arbitrary; but it hasthe number of vibrations and not on the nature of the sonorous been fixed by custom; and the la of the diapason represents body,
in musical language a sound of very determinate height; viz. Blowing Machine. In acoustics, a blowing machine is a that which corresponds to 880 simple vibrations; that is, 880: bellows, with a reservoir of air, which keeps up a continued l excursions of the particles of the sonorous body.
PARADIGM OF THE REGULAR YERB Avw, I LOOSE.-MIDDLE VOICE.
λε-λυ-μενος ω λε-λυ-μενος ας λε-λυ-μενος
Perfect; Tense-stem λε-λυ
σ. 1 λε-λυ-μαι
3 λε-λυ-ται D. 1 | λε-λυ-μεθον
3 λε-λυ-σθον* Ρ. 1 λε-λυ-μεθα
2 λε-λυ-σθε *
loose themselves; to loose one's self; to have loosed one's.
loosing one's self; loose yourselves; I have loosed mya Αυοιμην; λυσoιμην; λυομαι και λυωμαι και ελυομην; ελυσαμην ; | self; they have loosed themselves; they might have loosed λελυμαι; ελελυμην; λελυσομαι και λυσομαι και ελιπομην; λυονται ; | themselves; thou mayest have loosed thyself ; they shalH ελυοντο; ελυσαντο; λελυνται και ελελυντο; λελυμενος ω; have loosed themselves ; they remained behind; he may λυσαισθε και λελυται; λελυμενοι ωσι και λελυμεθα; λιπoιμην; have remained behind; do ye remain behind; let him loose λιπεσθαι; λιπομενος και λυσασθαι; λυεσθαι και λυομενος; λυσασθε; | himself; to have loosed one's self.
Conjugate, according to the active and middle paradigms, λελυμενος ειης; λιπωμαι.
these verbs aldevw, I instruct, educate; Baoulevw. I reign : ENGLISH-GREEK,
the chief parts are –παιδευω, παιδευσω, πεπαιδευκα, πεπαιI might loose myself; he might loose himself; they might | δευμαι; and βασιλευω, βασιλευσω, βεβασιλευκα, βεβασιλευμαι.
dious, and an elegant means of conducting many chemical LESSONS IN CHEMISTRY.--No. XXIV.
.-. . operations.
Until within the last few years, the most usual method of, BEFORE entering any further upon the investigation of chemi- employing.coal gas in chemical laboratories as a source of heat, eal bodies, it will be necessary to pause awhile and describe consisted in utilising the flame of a common argand burner, certain manipulative operations having reference to the appli- the construction of which is so well known that it scarcely cation of heat. An examination of the contributions to the need be detailed. At present, the argand burner is almost editorial letter-file points out the necessity of this. One thrown out of use by the mixed gas flame presently to be correspondent desires to know whether a gas flame may not described. be substituted for a spirit-lamp flame; another wishes to be The great advantage possessed by the mixed gas burner over instructed as to the best means of conducting distillation. I the argand flame is the absence of all smoke. The student shall proceed, therefore, in this lesson, to impart a notion of may here reply, that a well-regulated argand burner does not the economy of heat chiefly in reference to gas. Hitherto I smoke. True enough ; but it nevertheless deposits a thick have directed the employment of charcoal and of spirit as coating of smoke or soot on the surface of any body held sources of heat. This course was pursued in reference to the within it, whereas, on the contrary, a mixed-gas flame, if well necessities of those who could not command the agency of regulated, deposits no soot whatever. The theory of this soot coal gas, which whenever at hand, affords a cheap, commo- deposition cannot be understood, until we have fully investi- .'
gated the chemical nature of carbon. Suffice it to say, that If,
If, in the preceding experiment, the wire gauze be held at a the combustion of coal gas alone yields smoke, whereas the sufficient distance from the jet, and the resulting flame excombustion of coal gas and atmospheric air, or coal gas and amined, it will be seen to yield a very diminished amount of oxygen, the latter being the effective constituent in atmos- smoke; indeed, if the wire gauze be held exactly at the corpheric air, yields no smoke.
rect distance from the issue jet, a flame absolutely devoid of But most people know, I assume, that. a mixture of coal gas smoke may result. See now how these principles are applied and atmospheric air constitutes the terribly explosive fire-damp to the construction of a mixed gas burner. of the miner; how, then, are we to burn this mixture without Commence by taking an iron or brass or copper tube, having danger? Not only does this problem admit of being solved, an internal diameter of about two inches, and a length of about but the most explosive gaseous mixture in nature can be four. tranquilly burned by the method, slightly modified, that we Tightly whip, by means of wire, a sheet of wire gauze over shall adopt for producing the mixed gas flame, namely, outside one end of the tube, as represented at a, and scollop the other a piece of wire gauze, the effect of which material in checking end as represented at fig. 13. These directions being the progress of flame can be admirably recognised in the followed, the student will have made a contrivance for using following experiment, for conducting which, either a spirit. the mixed gas flame. lamp flame or a gas jet flame admits of being employed. Pro
Fig. 13, cure a piece of wire gauze (of copper wire by preference), and about six inches square. Hold this wire gauze horizontally over the apex of the flame, and gradually lower it to the base of the same, as represented in the annexed diagram, fig. 11.
By proceeding in this manner, the flame will be seen unable to extend through the wire gauze, that is to say, will be unable to traverse it and reappear at its upper surface. If a spiritlamp be employed, the extinguished gaseous contents which for the double purpose of admitting free passage to the atmos
The use of the scollops at the lower end of the tube b, is permeate the
gauze will be invisible; if, however, a gas flame be pheric air and to the end of a gas-pipe c, and the rationale of the the subject of experiment, the Folatile emanations will be seen instrument will soon be rendered evident. Very slight consi to be charged with smoke. Before proceeding to expatiate deration of what has been said will show that the conditions upon these phenomena, I ought to remark that a common of the arrangement are such as to cause the admixture of gas candle will serve the purpose of a gas flame, though on a with atmospheric air; which mixture ascending, must pass smaller, and therefore a less evident and less satisfactory through
the wire gauze layer at a, and escape. Being there scale. 'Two important facts will have been learned by the ignited, we get a flame rithout smoke, because the material performance of the preceding experiments. The first is, that burned is no longer gas, but a mixture of gas and atmospheric coal gas contains the matter of smoke, although it may not air. smoke on burning, and a spirit-lamp flame does not. second fact is, that flame cannot, or rather cannot readily, pass if not better than, is at least as good as any other. Nothing so
I have described this instrument in its simplest form, which, through small apertures. Advancing now a step further, the operator may demonstrate makers, these gentlemen devoting much time and material to
simple can be procured in the shops of philosophic instrument by means of a spirit-lamp, a gas jet, or a candle flame, that the manufacture of an apparatus very pretty to look at ceralthough flame does not pass through wire gauze, yet the gaseous material, the food of flame (thus to express one's self), tainly, but not better in practice than that just described. It
here be remarked, that the two great points to be attended Consequently it admits of being ignited on the other or to in the use of this instrument, are (i) to apportion the upper side of the wire gauze and conversely, supposing a gas amount of gas to that of air, and (2) to promote accurate admixjet employed (a spirit-lamp or candle will no longer aid our ture between the two. The former condition is secured by the illustration)-supposing, I say, a gas jet employed, and caused to very obvious means of a stop-cock, the second by well distripass through the wire gauze, that portion which traverses the buring the issue of gas: to which latter end one of a few very wire gauze may be burned on the upper surface of the latter, simple expedients will suffice. without the transmission of flame through the wire gauze down
Supposing the laboratory tube employed for conveying the to the orifice of the jet, fig. 12.
gas to be made of india-rubber or gutta-percha, to one end of Fig. 12.
it should be attached about a foot length of pewter or lead gastubing, a material which admits of being readily bent or otherwise manipulated. If such a terminal leaden pipe be made to open without further preparation directly into the cylinder, it is probable that perfect mixture of the gas and the air will not result; in which case the operator should proceed as follows.
Taking a pair of pliers, let him tightly compress the delirery end of the metallic tube as represented in d, or more evidently in the section ), fig. 14. In this manner it is evident the gas will be delivered in a sort of fish-tail jet, and an admixture sufficiently perfect will usually ensue. If not, little boles may be bored through the sides of the tube, until the exact condition of perfect admixture is achieved. This may be known to have occured when a piece of glass held in the flame is no longer covered with smoke. Let not the reader undervalue indeed the result described only occurs when the gas is in this seemingly rude apparatus. The writer possesses one of very small proportions as compared with the air; nevertheless, the dimensions indicated, which boils four quarts of water in the heat thus developed is very regular and gentle, and well a common iron kettle at the expiration of a few minutes. adapted for many chemical operations. If the amount of gas be
larger, the natural incandescence does not usually occur, but Fig. 14.
the inflammable mixture be ignited, the platinised stone will
increase the body and regularity of the flame. It may here be a
well to remark, that instead of the iron-plate chimney just described, one made by boring a hole in a large piece of pumicestone filed into the shape of a cylinder externally, is equally good, if not preferable. The further consideration of coal-gas as a source of heat, as well as the general principles of distillistion, must be deferred until next week.
; The discovery of the method of employing the mixed gas has been a great boon to chemists, enabling them to accomplish 33. The Semicolon is formed by a period placed above a by its means many results for which furnaces had been comma. hitherto required.
34. When you come to a semicolon in reading, you must in Although the flame produced by the method detailed is general make a pause twice as long as you would make at a powerful enough for the generality of purposes, its power comma.
35. Sometimes you must use the falling inflection of the Fig. 15.
voice when you come to a semicolon, and sometimes you must keep your voice suspended, as directed in the case of the comma. Whatever may be the length of the pause, let it be a total cessation of the voice.
That God whom you see me daily worship; whom I daily call upon to bless both you and me, and all mankind; whose wondrous acts are recorded in those Scriptures which you constantly read; that God who created the heaven and the earth is your Father and Friend, .
My son, as you have been used to look to me in all your actions, and have been afraid to do anything unless you first knew my will; so let it now be a rule of your life to look up to God in all your actions.
If I have seen any perish for want of clothing, or any poor without covering; if his loins have not blessed me, and if he were not warmed with the fleece of my sheep; if I have lifted up my hand against the fatherless, when I saw my help in the gate; then let mine arm fall from my shoulder blade, and mine arm be broken from the bone.
The stranger did not lodge in the street; but I opened my doors to the traveller.
If my land cry against me, or the furrows thereof complain; admits of being further increased. A very usual way of if I have eaten the fruits thereof without money, or have accomplishing this consists in superimposing a short chimney caused the owners thereof to lose their life; let thistles grow on the wire gauze top. This chimney affords convenient instead of wheat, and cockles instead of barley. bearing for little triangular supports of platinum or iron wire,
When the fair moon, refulgent lamp of night, o'er heaven's and these in their turn can be used for the support of crucibles, clear azure spreads her sacred light; when not a breath disretorts, &c. In the last diagram, fig. 15, a crucible" is repre- turbs the deep serene, and not a cloud o'ercasts the solemn sented thus exposed to the action of the flame.
scene; around her throne the vivid planets roll, and stars Modification of this Flame by Platinised Purnice Stone. -The unnumbered gild the glowing pole; o'er the dark trees a metal platinum, in the state of minute division, has the remark- yellower verdure shed, and tip with silver every mountain's able property of causing the ignition of inflammable gases. head; then shine the vales, the rocks in prospect rise, a flood Taking advantage of this quality, I have used it with great of glory, bursts from all the skies; the conscious swains, resatisfaction for the purpose of adding power, of modifying and joicing in the sight, eye the blue vault, and bless the useful imparting steadiness to the mixed gas flame.
light. To this end proceed as follows: Immerse small fragments
When the battle was ended, the stranger disappeared; and of pumice stone, about the size of hazel nuts, and irregularly no person knew whence he had come, nor whither he had, angular, in a solution of chloride of platinum, and ignite the gone. pieces to redness. By this treatment the pumice stone will be
The relief was so timely, so sudden, so unexpected, and so covered and imbued with metallic platinum in the finest state providential; the appearance and the retreat of him who furof division. If some pieces of this prepared pumice stone be nished it were so unaccountable; his person was so dignified heated so as to expel all moisture, ihen laid upon the wire and commanding; his resolution so superior, and his intergauze platform, and mixed gas passed between, the pieces will ference so decisive, that the inhabitants believed him to be an soon begin to glow like ignited charcoal, and this state of glow- angel, sent by heaven for their preservation. ing will continue as long as the gas is made to pass. Usually 36. Sometimes you must use the falling inflection of the the gas does not burst into flame under these circumstances; voice when you come to a semicolon, in reading.