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taste, and none the less 80 because he laboured generously to Sometimes in the course of a tune make music the property of the people, thus concludes: the music takes the “minor" charac

di “Let any one sing the above scales one after the other (four ter, introducing the new note Ne, and varieties of the so-called “minor scale"), and assuredly he will returns again to the ordinary use of i--f not be long in discovering which of the four is the most the common scale. Occasionally, too,

1 agreeable and natural, and most in the character of the minor the music pagses into the minor of the tonality (key). It is evident that the scales with leading notes 8OH KBY, making a new note, a tonule

d (NB), instead of being pleasing, are disagreeable to the ear, and below me, which to distinguish it

ti-tu, impracticable to the voice. The absence of the leading (note from NB of the original key) we call d f (NE) on the contrary often gives to the melody something majestic NU; and, not unfrequently, it enters ti and solemn. The Gregorian chant, so remarkable for melodious the " minor" of the PAH KEY, origi

n.no, beauties, affords many proofs of this, and also the popular nating another note, a tonule below RAY melodies of different countries, especially those of Ireland and (r'), which we call' ni. The modula- ni,, Scotland, so much admired by the greatest musicians." Surely tor" at the side will illustrate these

82

d fi here is example and testimony enough to prove these notes— changes. whether good or bad—at least non-essential and arbitrary, One question yet remains. Should not the scale on which

Another “transition " into what is called the “minor of the

tem. minor tunes are framed be still treated as a distinct one, and same tonic" (pou becoming LAH), is more proper to “ something more than the common scale used in a peculiar pered" musical instruments than to music itself or the unaided manner ? To which we answer-Yes, if it is distinct; but, if voice. You may treat it as transition into the key of us flat, otherwise, why multiply difficulties and conceal the truth or, retaining the syllables of the original key, the new notes But it clearly is not, in any particular, distinct. First, in refer- may be treated as chromatic. Thus you will have the oddly. ence to the character” or musical effect of the notes--the most sounding notes Mow, Low, and tow, as any one may perceive important particular of all the notes of the so-called minor by drawing the two keys side by side, and bearing in mind the scale correspond precisely with those of the common one (rec- difference between the tonule and the chromatic part-tone. koning from law to Lan) Not a single note of the common

Our pupils will now be able to ransack the stores of classical scale changes its character when used in a minor tune. Lau is music, and to take their “part" in fireside glees, at their pleastill the sorrowful, te the piercing, pay the awe-inspiring note, sure. They will be very largely, and, we hope, very long, re&c., as before. Next, in reference to the exact intervals be- warded for all the patience and painstaking which we ha.-e tween the notes—they are precisely the same as those of the demanded of them. common scale (from Lau to LAH') with only this peculiarity, that the graver (flatter) position of the “ variable note ordinarily used in tunes of this character, whereas it is only ON PHYSICS OR NATURAL PHILOSOPHY. ocoasionally used in other tunes. Premising that from Dou to

No. XIX. DOH' is commonly called by musicians a major key (beginning with a major, or greater, third, dou ME), and that a minor key

(Continued from page 261.) beginning on a note in the position of our LAH would be called

THE ELASTIC FORCE OF GASES. its relative minor, let

us quote the following testimonies to the last point. Colonel Thompson says – The change to the

rela: air increases in proportion to its density, was first proved by

Experiments of Boyle. The principle that the elastic force of minor reduces itself to avoiding the acute second of the old Boyle in 1660, in the following manner :He took å uniform key (r) and using only the grave (r').” (See “ Westminster

tube A B C, fig. 79, closed at c and open at a, Review,” April, 1832).

Fig. 79, Dr. Crotch says—" Some authors and bent upwards so that the part on was make it” (the first note of the principal minor key) “ the same parallel to the part Am. Mercury was poured as the note Law of the relative major key, viz., A in the key of in at the open branch a until the level in both (smaller tone-of eight degrees) “above o

branches of the tube stood at x and x respec(808). In that case all the natural notes excepting P (RAY) of the same density as the external air in the

tively, and the air in the closed branch on was correspond with those of the major key of c.(See Crotch's · Elements" -Tuning, &c.) Turning to his illustrative plates, sured and found to be 12 inches; the pressure

branch AM.

The distance on was then mea. we find the scale of minor tunes requiring the smaller tone (eight degrees) between DOH BAY, and the larger tone (nine in both branches was equal to 30 inches of a larger tone between DOH RAY and a smaller one between branch Am above the level of that in the shorter degrees) between RAY MB, while other tunes usually require mercury, being that of the atmospheric air ;

In fact the variable note assumes its grave position. But it sometimes does the same in the common scale. Is this,

branch was 0. More mercury was poured in then, a peculiarity sufficient to establish a new scale : More at a, until the distance on was diminished to 10 pver, is it not natural to suppose that the common scale, which inches, and the mercury stood in the longer is found to be essentially the musical scale of all nations, must branch 6 inches above that level; the pressure hold a peculi ar accordance with the ear and the sympathies of in both branches was now equal to the atmothe human race? and is it not proper, therefore, to consider spheric pressure, 30 inches of mercury, and 6 this as the one scale, and everything else that cannot establish a inches of mercury additional, or 36 inches in distinct and independent character as but a modification or å all; more mercury was again poured in at a, peculiar use of it? It is certain that great detriment must be until the distance en was diminished to s done to the mind of our pupils, and great hindrance given to inches, and the mercury stood in the longer their progress, if we first cause them to study and practise our branch 16 inches above that level; the pressure theory, of a new and self-contradictory minor scale, and then in both branches being now equal to the atmospheric pressure leave them to discover that, in music itself, instead of the arti- and 15 inches additional, or 45 inches in all. The experiment ficial difficulties they have so laboriously mastered, there is only follows:

was repeated again and again, and the results tabulated as to be found the common scale, 80 used as to produce a peculiar effect and the merely occasional, non-essential, introduction of a new note !

Distances from c Heights of Mercury" Pressures in both

in AX abovo its (We were present, in October last, at i several choral performances

branches of the branch,

level in cn. of pupils who were taught to sing on the inethod developed in these

tube. lessons, some of which were attended by more than 3,000 people. We

12 inches

0 inches

30 inches saw a choir of children who sang music at first sight, a thing quite new

10

6

36 1) us. The “ Tonic Solfa Association " numbered 2,000 pupils in Lon.

8
15

45 ('alone last year, and the meetings referred to were the means of

6
80

60 o ginating at once three new classes of about 200 pupils ench. We

60

90 may claim, for the POPULAR EDUCATOR, the credit of giving a commopolitan influence to these valuable efforts.)-ED.

The distances from c to x in the shorter pranch diminishing

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us the heights of the mercury in the longer branch, and conse- ever the level in both branches is not the same. Mercury is quently the pressures in both branches, increase, proves that again poured into the larger branch until the pressure which the densities of the air in the shorter branch increase as the arises from it reduces the air contained in the smaller branch spaces diminish ; and that the elastic force of the air, mea- to one-half its volume; that is, this volume, which was at first sured by the pressures, is proportional to its density; for we measured by 10 on the scale, is now reduced to 5, as shown in have, by comparing the distances in the first column with the fig. 80. Now, measuring the difference of level cA between pressures in the third column, the following inverse pro- the mercury in the two branches, we find that it is exactly portions :

equal to the height of the barometer at tlte moment when the 12 : 10 :: 36 30

experiment is made. The pressure of the column c A is there10 8 45

fore equivalent to that of one atmosphere; by adding to it 36 8 6 60 : 45

the atmospheric pressure which acts at.c, at the top of the 4 90 60

column, we see plainly that at the instant when the volume of

air is reduced to one-half, the pressure is double of that which These proportions clearly show that the pressures, and conse- it was at first; which proves the truth of the law in this case. quently the densities, are inversely as the spaces occupied by

If the greater branch of the tube were long enough to admit the same quantity

of air ; whence it follows that the elastic of mercury being poured in till the volume of air in the smaller force of air is proportional to its density.

branch was reduced to a third of what it was at first, we should Mariotte's Law. Mariotte, a French philosopher, was the find that the difference of level in the two branches'is equal to next experimenter who established the same principle in 1668, twice the height of the barometer ; that is, it is equivalent to by the announcement of the following law, which has ever the pressure of two atmospheres, to which adding that

which since borne his name, viz. :-" That the volume of any quantity acto directly on the surface of 'the mercury in the greater of gas, at a given temperature, will diminish in the inverse ratio branch, gives a pressure of three atmospheres. It is therefore of the pressure to which it is subjected." This law is verified under a triple pressure that

the volume of air is reduced to in the case of air by means of the following apparatus :-On one-third of its volume. The law of Mariotte has been experia wooden board placed vertically, is fixed å glass tube bent mentally verified in the case of air by MM. Dulong and

Arago, as far as 27 atmospheres, by means of an apparatus Fig. 80.

similar to that now described. In order to demonstrate the truth of the law for any gas, the apparatus must be modified to admit of the introduction of the particular gas in question.

The law of Mariotte has been verified also in the case of pressures less than that of the atmosphere. Thus, a barometric tube being filled only to about two-thirds of its length, the other third containing air, it is inverted and immersed in a deep jar or vessel full of mercury, fig. 81; the tube is then sunk in the vessel until the level of the mercury be the same within and without the tube; the volume of the air contained in the tube is determined by a scale fixed to the vessel, this air being now under a pressure exactly the same as that of the

Fig. 81.

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upwards in the form of an inverted siphon ; that is, having two unequal branches, see fig. 80. Alongside of the shorter branch, which is closed at the top, there is placed a scale indicating equal capacities or volumes in the parts of the tube corresponding to the parts of the scale ; and alongside of the longer branch there is also placed a scale indicating equal altitudes in centimetres. The zeros of the two scales are on the same horizontal line.

atmosphere. The tube is now raised, as shown in the figure, In order to make the experiment, mercury is poured into the until, by the diminution of the pressure, the volume of air is tube at the top of the longer branch, so that the level of this doubled, as shown by the scale; it will then be found that the liquid may correspond to the zero of the scales of the two height of the mercury in the tube at A is the half of the true branches, a result which may be obtained by several trials. height of the barometer. The air of which the volume is thus The air contained in the shorter branch is then subjected to the doubled, is therefore submitted to a pressure of only half an atmospheric pressure, which acts in the greater branch, when- atmosphere, for it is the elastic force of this air which, united

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to the weight of the raised column, balances the pressure of the the mercury, becomes stationary in the glass tube, the figure exterior atmosphere. The volume of the air is therefore still ! is marked, signifying one atmosphere; then, proceeding in the inverse ratio of the pressure to which it is subjected. from this point by 30 inches at a time, the

In the experiments just detailed, the mass of air in the tube figures 2, 3, 4, 5, and 6, which indicate the 82, remaining the same, its density becomes greater in proportion number of atmospheres, are marked, because as its volume is reduced ; whence we deduce the following as a column of mercury of the height of 30 a consequence of the law of Mariotte, that, " at a given tem- inches represents the pressure of the atmo, perature, the density of a gas is proportional to the pressure sphere. Then the intervals from 1 to 2, 2 to which it sustains.". Consequently, under the ordinary pres- 3, &c., are divided into ten equal parts, sure of the atmosphere, the density of air being a 770th part which give the tenth parts of an atmosphere. of that of water, it follows that, under a pressure of 770 atmo- If the tube A be now put in communication, spherés, air would have the same density as water, if at such a for example, with a steam boiler, the mercury pressure it would be still a gas.

will rise in the tube'B D to a height which Till recently, it has been considered that the law of Mariotte measures the tension of the steam. In the was true for all gases and under all pressures. M. Despretz was igure, the manometer is shown as marking 4 the first who showed that this law ceases to be strictly true when atmospheres, which are represented by 3 the gases are subjected to a pressure nearly equal to that which times the height of 30 inches, besides the produces their liquefaction. Lastly, M. Regnault has proved that atmospheric pressure at the top of the this law does not apply equally to all gases. Thus, air and nitro- column. This kind of manometer is only gen are compressed a little more, and hydrogen a little less than used for pressures which do not exceed 6 or 6 that which it indicates. In the case of carbonic acid, it does not atmospheres. Beyond this point it would be even furnish an approximation to the truth when the pressure is necessary to make the tube so long that it considerable.

would be easily broken. In this case, recourse Applications of Mariotte's Law. The following examples of must be had to such a construction as that, the application of this law may be useful to students of Chemistry explained in the next paragraph. and Physics.

Compressed-air Manometer:- This manome1. A vessel in which air can be compressed contains 4.8 galater, founded on the principle of Mariotte's lons of air, the pressure measure by the barometer being 29.6 law, is composed of a strong glass tube closed inches; what will be the volume of air at the pressure of 30•4 at its upper extremity and Elled with dry air. inches? If denote the volume required, we have,

This tube is immersed in a cistern partly filled

with mercury, to which it is cemented. The
3:4:8:: 29.6 : 30-4; whence,

cistern, by means of a side tube A, fig. 83, is
29.6 X 4:3
=4:1866 gallons.

put in communication with a close vessel,
304

which contains the gas or vapour whose 2. Having 20 gallons of gas under the pressure of one atmo: graduation of this manometer, the

quantity

elastic force is to be ascertained. As to the sphere; to what pressurs must it be subjected, in order to reduce it of air contained in the tube is such, that to 8 gallons ?

when the orifice A communicates with the If p denote the pressure required, we have,

atmosphere, the level of the mercury is the p:1:: 20 : 8; whence,

same in the tube and in the cistern, 'At this
20 x 1

level, therefore, 1 is marked on the board to
P=
24 atmospheres,

which the tube is attached. In continuing

the graduation, it is necessary to observe 3. A gallon of air weighs 20 grains at 32° Fahrenheit, the that the pressure which is transmitted through barom

ric pressure being 30 inches; what will its weight at the tube increasing, the mercury rises in the the same temperature, when the pressure is 28 inches ?

tube until its weight, added to the tension If w denote the weight required, we have,

of the compressed air, balances the exterior w: 20 :: 28 : 30 ; whence,

pressure. If, therefore, we mark 2 atmo

spheres in the middle of the tube, we shall
20 X 28
= 184 grains.

commit an error; for, when the volume of
30

air in the tube is reduced to one-half, its The Manomoter. The name manometer (from the Greek, rarity- tension, by the law of Mariotte, is that of two measure) is generally applied to instruments employed in measu- atmospheres; and, therefore, when increased ring the tension of gasos or vapours when it is greater than tha by the weight of the column of mercury which pressure of the atmosphere. There are various kinds, as the free-is elevated in the tube, it represents a pressure greater than air manometer, the compressed-air manometer, and the metallic two atmospheres. The number 2 must not therefore be manometer. In these different kinds, the

unit of measure which marked in the middle of the tube, but a little lower, and is employed the atmospheric pressure, when the barometer at such a height that the elastic force of the compressed stands at 30 inches. Now, we have seen that this pressure on a air, added to the weight of the column of mercury in the square inch is 144 lbs.; consequently, if we say that a gas has tube, shall be equal to two atmospheres. By such a calcua tension of two or three atmospheres, we mean, that it aots on the lation as this, the exact position of the figures 2, 3, 4, &c., sides of the vessel which contains it with a pressure of twice or

on the scale of the manometer is determined. This inthrice the weight of 144 lbs. per square inch.

strument is not very accurate when the pressures are great; Free-air Manometer. --This manometer is composed of a strong for the volume of air becoming less and less, the divisions of glass tube B D, fig. 82, about 58 yards long, and a cistern | the scale approach too near to each other. D, made of iron, containing the mercury in which the tube is The inconvenience of both the preceding instruments has immersed. This tube is cemented to the cistern and fixed on a been attempted to be remedied by employing an apparatus of board, along side of which is placed another tube a c, made of the following description, fig. 84, Nos. 1 and 2. This manoiron, and about 5 yards long; by means of this tube the pressure meter, invented by M. Richard, and of which No. 1 is the of the gas or of the vapour is transmitted to the mercury in the front view, and No. 2. the side view, is of the free-air descripcistern. As manometers of this kind are most frequently tion, indicates very high pressures, and is of a very moderate used in cases where vapour of high temperature, or steam, height. It consists of a tube doubled several times on itself, would soften the cement which is employed to fix the glass so as to present a series of vertical branches connected with tube to the cistern, the tube a c is filled with water; and it one another by bent knees; that is, the instrument presents a is by this means that the pressure of the vapour is transmitted continued series of siphons in the same vertical plane, alterto the mercury.

nating up and down and having the same vertical branches. The In order to graduate the manometer, the orifice A is allowed columns of mercury are separated by columns of water, which to communicate with the atmosphere, and at the level where occupy the upper bent knees and the upper half of the height

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of the branches. The apparatus being completely filled with the columns of mercury. This correction will be made by columns of mercury and water, if one of the extremities of the multiplying the preceding product by the fraction 38, which tube be put in communication with the vessel of gas or vapour represents the ratio of the excess of the density of mercury whose tension is to be ascertained, the other extremity remaining above that of water, to the density of mercury. The doubled open to the free-air, the excess of the pressure in the vessel over tube is made of iron ; the second vertical branch

open to the air is mounted with a glass tube to show the extremity of the Fig. 83.

column of mercury; and the scale, which is made of brass, is graduated to atmospheres.

Metallic Manometer.-M. Bourdon, a mechanician of Paris, bas recently invented a new manometer, represented in fig. 86

that of the atmosphere will produce the elevation of the level of the mercury in all the branches; these elevations will be of This instrument, which is wholly metallic and without meroury, equal height if the tube be of the same bore throughout; and is constructed on the following principle, discovered by the in this case, the effective pressure of the gas in the vessel will inventor; when a tube having flexible sides and a slightly flat

tened or oval shape is wound up in the form of a spiral, in the Fig. 84.–Nos. 1 and 2.

direction of the less diameter, every interior pressure on the sides No. 1.

No. 2.

has a tendency to unwind the tube; and, on the contrary, exterior pressure has a tendency to evind it up.

According to this principle, the manometer of M. Bourdon is composed of a brass tube, about 24 feet long, having its sides thin and flexible. A section aeross the tube, represented at 8 on the left in the figure, is an ellipse whose greater axis is about to of an inch, and smaller axis about its of an inch. The extremity a, which is open, is fixed to a tube with a stop-cock d, for the purpose of putting the apparatus in communication with a steamboiler.

The extremity b is closed, and moveable like the rest of the tube. Now, when the stop-cock d is open, the pressure which is produced by the tension of the vapour on the interior sides of the tube causes it to unwind. The extremity b is then drawn from left to right, and with it an index e, attached to it, which indicates on a dial-plate the tension of the vapour in atmospheres. This dial-plate is previously graduated by means of a free-air manometer, by putting the apparatus in motion with compressed air. This manometer has the great advantage above the preced ing, manometers, of being extremely portable and not easily broken. It is now in operation in the locomotives upon several railroads in France.

Metallic Barometer.-M. Bourdon is also the inventor of a metallic barometer founded on the same principle as his manometer. This apparatus, represented in fig. 86, is composed of a tube similar to that of the manometer, but shorter, hermetically closed, and fixed at its middle point; so that the vacuum having been made in it beforehand, whenever the atmospheric pressure

diminishes, this tube unwinds itself in consequence of the principle zwa Liter Wabove mentioned. The motion is thus communicated to an index DOTTI onl of our tout to sluding

which indicates the pressure of a dial-plate. As to the trans

mission of the motion, it is effected by means of two small wires nagy de montato stilar; bis 7

b and a, which connect the extremities of the tubes with a lever be given by the height to which the mereury is raised above fixed on the axis of the index. If the pressure increases instead the point of departure in the open branch of the tube, multiplied of diminishing, the tube will close in upon itself, and there is a by the number of vertical branches, minus the correction due to small spiral spring at e, which then brings back the index from the influence of the weight of the intermediate water between right to left, under the dial-plate. This barometer is of small

size, very sousible, and remarkable for its very great simplicity of Al gases which do not act chemically upon each other, when construction,

subjected to the same experiment, give the same result; and it is Luws of the Mixture of Gases. When two or more gases are remarked that the mixture acts more rapidly in proportion to the inclosed in the same vessel, their mixture, when not effected by greater difference of densities between the gases. The second chemical combination, is regulated by the following laws : law is proved experimentally by the help of the manometer. It Fig. 86.

Fig. 88.

[graphic][subsumed][merged small]

1st. The mixture, which always takes place rapidly, is continuous and homogeneous, so that all the parts of the whole mass contain the same proportions of each gas.

2nd. The sides of the vessel where the mixture takes place is found also that if the gases are mixed at the same pressure, being inextensible, and the temperature

constant, the elastic force before and after the mixture, the volume of the mixture is equal of the mixture is equal to the sum of the elastic

forces to the sum of the volume mixed, it being of course understood of the gases contained in the mixture, when each is referred to that the mixture takes place in a vessel whose sides are inesten, the whole mass, according to the law of Mariotte.

sible. The first law is a consequence of the extreme porosity and Mariotte, in the same manner as simple gases; that is a fact

Lastly, gaseous mixtures are subject to the law of expansive force of gases. It was first proved by the French which has been already proved in the case of air, which is a ahemist Berthollet, by means of the apparatus shown in fig. 87, mixture of oxygen and nitrogen.

Fig. 87.

[graphic]

LESSONS IN CHEMISTRY.-No. XVIII.

Consideration of the Results of Combustion in Oxygen Gas.--The experiments performed in our last lesson require that we should now investigate the theory of combustion.

We have seen every instance of combustion which has hitherto come under our notice to have been the result, or at all events the concomitant, of the union of the combustible with oxygen as the supporter. In point of fact, almost all instances of combustion are the result of the powerful action of oxygen upon combustibles : not all, however, as was formerly supposed; hence the definition of combustion, formerly accepted, namely, “rapid union of a combustible with oxygen," is not strictly true. Chlorine, iodine, bromine, sulphur, and perhaps certain other elements, may in some cases take the place of oxygen as supporters of combustion. The only definition of combustion justified by known facts is, “rapid chemical action attended by the evolution of light and heat."

The result of the combustion of substances in oxygen gas may be an oxide, an acid, or an alkali, according to the nature of the combustible. The first and second we have generated

in the course of our preceding experiments; the third we shall which is composed of two glass globes, each furnished with a neck) form hereafter. and stop-cock, and screwed to each other. The upper globe was Returning now to a consideration of the contents of the jars filled with hydrogen, of which the density is .0692, and the other or bottles in which our various substances were deflagrated, globe with carbonio acid, of which the density is 1.529 or 22 let us begin with that vessel in which the iron was burned. times greater than the former. The apparatus was placed in the You will observe, scattered all over its sides and base, various cellars of the Observatory at Paris, in order to keep them from little globules of a material not unlike iron to look at. If you being shaken, and from every variation of temperature. The remove these globules from the vessel, you will find them to stop-cocks being then opened, as in fig. 88, the carbonic acid be heavy and hard ; not unlike the original iron in appearance, in the lower globe B, notwithstanding its greater weight, passed but more dull. In reality, they are a compound of oxygen partly into the upper globe A, and, at the end of a little time, it with iron, or, in other words, the oxide of iron, " the black was observed that the two globes contained equal proportions of oxide,” as we may call it, by way of contradistinction to iron hydrogen and carbonic acid.

rust, or “red oxide" of that metal.

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