surfaces from and to which the sound is allowed to play. Distinctly marked echoes of this combined and planned order, may sometimes be heard in the vaults of cathedrals, in which case the waves of sound are driven from side to side of a deeply groined arch, and reverberate in protracted peals. One of the most interesting echoes of this kind in nature, is that which occurs on the banks of the Rhine at Lurley. If the weather be favourable, the report of a musket, fired on one side, is repeated from crag to crag, on opposite sides of the river alternately, as represented in fig. 24. P is considered as the primary point of radiation for the sound, and crossing the river it strikes at 1, then is sent off to 2, and so on to 3 and subsequent points, stopping or faintly dying away opposite E. form of apartment for the proper distribution of sound, is that in which the length is from a third to a half more than the breadth, the height somewhat greater than the breadth, and having a roof bevelled off all round the sides. This species of ceiling, called technically a coved or coach roof, from its being lower at the sides than centre, is in all cases best suited for conveying sounds clearly to the ears of auditors. MUSICAL SOUNDS. There is a peculiar character in sounds, depending on the character of the sounding body. A blow with a hammer, or the report of a pistol, produces only a noise. But if a body be of such a thinness and tightness as to produce a succession of impulses of a sufficient degree of quickness, a tone is the result, namely, a sound composed of a great number of noises, all so close upon each other that they bring but one result to the ear. Wires and strings of metal and catgut, slips of metal, fine membranes, and columns of the air itself enclosed in tubes, are the most familiar means of producing sounds of this kind. Such sounds are said to be musical. The study of musical sounds, as a branch of natural philosophy, is calculated, perhaps, to give as much pleasure to the man of science as music itself can convey The natural character of these sounds, and their relato those who are gifted with what are called good ears. tions to each other, are very remarkable; while the relation of the whole to the human mind must be regarded as one of the most interesting proofs of creative design which the entire circle of nature presents. sing or play, and having seen the key-board of a pianoforte, will be ready to say that there are more notes than seven; but there are only seven that are, strictly speaking, various. The voice or an instrument may run up into other notes; but all of these are repetitions of the first seven, and identical respectively with them, in all respects except shrillness. In ordinary pianofortes, there are at least six repetitions of the seven the voice of a child, while the lowest rumble like a notes, so that the uppermost keys are more peepy than There are some remarkable echoes in ecclesiastical structures, arising from peculiarities in the construction. In erecting the baptistry of the church of Pisa, the The principal sounds of music may be said to be only architect, Giovanni Pisano, disposed the concavity of seven in number. There are other five, which may be the cupola in such a manner, that any noise from be- produced by the voice with some little difficulty; but low is followed with a very loud and long double echo. the voice, in an untutored condition, gives forth only seven. The notes are of different degrees of shrillness, Two persons whispering, and standing opposite to each other, with their faces near the wall, can converse toge-knows nothing of music beyond having heard another one rising above another in succession. A person who ther without being overheard by the company between. This arises from the elliptical form of the cupola, each person being placed in the focus of the ellipse. In the cathedral church of Gloucester, there is, or was lately, a whispering gallery above the eastern extremity of the choir, which extends from one end of the church to the other. If two persons, placed at considerably distant points, speak to one another in the lowest voice, it is distinctly heard. A similar effect is produced in the vestibule of the Observatory of Paris, and in the cupola of St Paul's, in London. A tourist has mentioned, that in Italy, on the way to Naples, and two days' journey from Rome, he saw in an inn a square vault, where a whisper could easily be heard at the opposite corner, but not at all on the side corner that was near to you. This property was common to each corner of the room. He saw another on the way from Paris to Lyons, in the porch of a common inn, which had a round vault. When any person held his mouth to the side of the wall, several persons could hear his whisper on the opposite side. The whispering gallery in St Paul's, London, is a great curiosity. It is 140 yards in circumference, and is just below the dome, which is 430 feet in circumference. A stone seat runs round the gallery along the front of the wall. On the side directly opposite the door by which visiters enter, several yards of the seat are covered with matting, on which the visiter being seated, the man who shows the gallery whispers with the mouth near the wall, at the distance of 140 feet from the visiter, who hears his words in a loud voice, seemingly at his ear. The mere shutting of the door produces a sound like a peal of thunder rolling among the mountains. The effect is not so perfect if the visiter sits down half way between the door and matted seat, and much less if he stands near the man who speaks, but on the other side of the door. It is of great importance that buildings designed for large auditories should be constructed in such a manner that the voice of the speaker will neither echo from the walls nor be lost to the hearers. The best known drum. Si, or by the first seven letters of the alphabet in a peThe seven notes are named Do, Re, Mi, Fa, Sol, La, culiar arrangement, namely, C, D, E, F, G, A, B. They are thus represented in the well-known language which musicians present to the eye (using the treble clef): C D E F A B Let an ordinary piece of catgut or violin-string be extended between two points on a board, and screwed up. It may be made, according to its length and degree of tension, to vibrate when struck exactly two hundred and forty times in a second. The note which it thus produces is C, or Do; and a man, on trial, will find that this is the note with which he is most apt to begin a song, when he attempts to sing. The note in his voice will be perfectly in unison with the note produced by the string; that is to say, they will melt into and agree with each other, and the effect will be pleasant. This is because the membrane at the top of the singer's windpipe (the instrument of his voice) vibrates exactly the same number of times in a second, producing that note, as the string does. The equality in the number of vibrations is what makes the notes the same, and the effect harmonious and agreeable. We shall suppose the string to be forty-five inches long that produces the note C of 240 vibrations in a second. Being extended between two pegs near the surface of a board, the experimenter may place his finger upon it right in the centre, and twang or strike either half, when he will find a much shriller note produced, being, in reality, the first C, or Do, of a new series of the seven notes. In this case, the vibrations are exactly double, namely, 430 in a second, these being always the more rapid the shorter the string or the greater its tightness. The second or upper C is called the octave of the first, being the eighth note above it. Cor Do (octave), 224 in. 480 vib. A or La, 27 in. 400 vibrations. OG or Sol, 30 in. 360 vibrations. We shall now suppose that the string is shortened only so far as to leave thirty inches, or two-thirds of its length, free for twanging. This shorter string will sound the note G, or Sol. In this case, as the length of string is two-thirds, so are the vibrations threehalves, or one and a half. times those in the former instance, namely, 360. All the other notes are produced by different proportions of string and numbers of vibrations, as shown - Cor Do, 45 in. 240 vibrations. in the adjoining scale : F or Fa, 331 in. 320 vibrations. D or Re, 40 in. 270 vibrations. longer strings of the harp or pianoforte is struck, there is not only a vibration along the whole length, giving it an elliptical appearance, but there are also vibrations of shorter lengths of the same string going on at the same time. It has been found, when light pieces of paper are hung across the string, that they settle at certain places, showing that the principal subordinate vibrations correspond with octaves, fifths, and thirds. A drum, or a sonorous board, over which sand has been strewn, will, if beat, throw the sand into curious figures of a determinate and regularly recurring character. This is the result of similar subordinate vibrations along the extent of the sounding body. 66 There are even more curious facts connected with the harmonious notes. The cries of a city-that is, the scarcely articulate, but often very musical, sounds uttered by persons selling things on the streets-generally rise on thirds or fifths, sometimes on octaves; and this although few of these poor people have ever been taught music. The cry of oysters by women in Edinburgh is always on an octave. Teachers of elocution are also aware that human beings in general make such transitions of voice naturally, under the influence of certain feelings. For example, a person indifferently surprised at hearing a friend say "I was the person who did so and so," will say, "Was it you!" rising only a third at the last word. If greatly surprised, the rise will be a fifth. There may even be so great a degree of astonishment, that the word "you" will begin on one note and terminate on its octave. The answers, "Yes, it was I," will show corresponding declensions or falls of voice. We thus see how truly music is a species of natural language. Unquestionably, every shade of human feeling can be represented by successions of its sounds, apart altogether from words. What is remarkable here is the curious mathematical proportions on which the various notes depend. Taking the first C as one, and its octave as one-half, we have various lengths of string for the intermediate notes, in the following proportions: namely-for D eight-ninths, for E four-fifths, for F three-fourths, for G two-thirds, for A three-fifths, and for B eight-fifteenths; all of which proportions are exactly reversed with regard to the numbers of vibrations, these being in succession nine-eighths, four-fifths, &c. The proportions, as clearly appears to the eye from the above scale, are not regular: the string is first shortened five inches, then four, then two aud a quarter, next three and three-quarters, and so on. Nevertheless, these are the musical notes which the voice naturally gives forth, and which the mind recognises as beautiful. The string twanged at lengths of what would appear more regular proportion, would give forth musical sounds, but not the seven notes of music-not those peculiar sounds which all nations recognise as such, and which nature has manifestly appointed to serve in that cha-vibrations sometimes predominate, and yield the clear With respect to the sounds produced by wind instruments, the effect is caused by the vibrations of a column of air confined at one end, and either open or shut at the other. The length of the sounding column determines the nature of the vibrations; but along with the fundamental tone, there are interior and subordinate vibrations. The whole colunin divides itself into regu lar portions, equal to the half, the third, and so on, of the longitudinal extent, in the same manner as we showed was the case in stringed instruments. We may observe something similar to these vibrations in the contraction and expansion of a long and very elastic string, to one extremity of which a ball is attached. A spiral spring also shows, and perhaps more clearly, the repeated stretching and recoil. If suddenly struck at one end, it will exhibit not only a vibration throughout its whole extent, but likewise partial ones, which wind vermicularly along the chain of elastic rings. If the air be struck with great force, the subordinate racter. Irregular as the proportions appear, there are some of the seven notes which are more proportioned to each other than the rest. They are said to be more in harmony with each other; and the effect when they are struck together is pleasing. It is to be observed in the first place, that a note always harmonises well with its octave, or the eighth or repeating note above it. This is supposed to be because the vibrations of the one note in that case are exactly two for one of the other. The first Do also harmonises well with Sol (G), which is called its fifth, being the fifth note above it; and this is, on the same supposition, because the vibrations are in that case as three to two, which is also a symmetrical proportion. Harmony is also produced when some other notes are sounded at the same moment with those which are third above them (their thirds); and this may be accounted for in a similar way. Thirds, fifths, and octaves, are therefore pleasing or harmonious sounds, while seconds, fourths, sixths, and sevenths are less so. Experiments of a very curious nature have been made on this subject. It may readily be observed by the naked eye, that when one of the est and loudest tones. This may be observed in the dying sounds of a bell, which rise one or two octaves, and expire in the acutest note. Upon the degree of force with which the instrument is blown, depends the performance of the bugle-horn, whose compass is very small, consisting only of the simplest notes. In other wind instruments, the nature of several notes produced depends upon the length and size of the tube, or the positions of the holes in its sides. In the organ, there is a pipe for each note, and wind is admitted from the bellows to the pipes by the action of keys similar to those of a pianoforte. The organ may be played also by a barrel made to turn slowly under the keys, and to lift them in passing, by means of pins projecting at certain determinate intervals from the surface of the barrel. In wind instruments which are furnished with reeds, the tone depends on the stiffness, weight, length, &c., of the vibrating plate or tongue of the reed, as well as on the dimensions of the tube or space with which it is connected. Printed and published by W. and R. CHAMBERS, Edinburgh. Sold also by W. S. Orr & Co., London. CHAMBERS'S INFORMATION FOR CONDUCTED BY WILLIAM AND ROBERT CHAMBERS, EDITORS OF CHAMBERS'S NUMBER 55. NEW AND IMPROVED SERIES. CHEMISTRY. PRICE lid. THE material world immediately under our observation, including such parts of the earth's crust as have been explored, the plants and animals upon its surface, and the atmosphere which envelops it, is found to consist of fifty-four simple substances, just as all the words which compose a language are resolvable into a few letters. These substances, having hitherto resisted all endeavours to divide or resolve them into any others, are termed the elements of matter, or simple bodies. From the earliest stage of creation most of them appear to have been in a state of combination with each other; they are scarcely ever found otherwise. Matter has ever been, and is now, undergoing perpetual decompositions and recombinations, some of which take place upon an extensive scale, as part of the regular functions and operations of nature, while others are effected by the ingenuity of man, to serve the purposes of his ordinary economy. Of the fifty-four simple substances, six are gases (three of which only are permanently gaseous), forty-one are metals, and the remaining bodies are reducible under no fixed class. The investigation of the laws under which these various elementary bodies have formed the numerous compound substances which we see in nature, and the means by which compound substances can be resolved into their original elements or thrown into new combinations, are the objects of the science of Chemistry. The term chemistry is of doubtful derivation; but it seems to have been applied at an early period to various methods of melting or preparing metals, and was identified with the visionary science of alchemy, which professed to be the art of transmuting copper and other base metals into gold and silver. It is only within the last sixty or seventy years that chemistry has risen to the rank of a science; but during that period it has advanced towards perfection with a rapidity unparalleled in the history of philosophy. The applications of chemistry are universal. There is no science so immediately conducive to human comfort. To whatever art or manufacture we turn our attention, we find that it has either been created by chemistry, or owes to it some of its greatest improvements. In the present sheet, it is our object to present a simple and intelligible view of the principles of this exceedingly important science, with a description of the various elemental bodies, and their more immediate combinations. We shall commence with a view of the general leading principles on which the science proceeds. CHEMICAL ATTRACTION. When particles of different kinds of matter are brought into contact, they frequently unite and form new substances, differing widely in many instances from those by whose union they have been formed. This is called chemical attraction, or chemical affinity, because it is said that the particles of certain bodies, having an affinity for each other, will unite, while others, having no affinity, do not readily enter into union. It might almost be supposed that there are such things as preferences and dislikes among the particles of matter. Thus, if a piece of marble be thrown into vitriol or sulphuric acid, their particles will unite with great rapidity and commotion, and there will result a compound differing in all respects from the acid or the marble. This is at once an instance of affinity between two substances, and an exhibition of stronger and weaker affinity. The commotion or effervescence in the experiment, results from the disengagement of a gaseous (carbonic) acid in combination with the basis of the marble, in consequence of the vitriolic acid having a stronger affinity for it. When a piece of caustic magnesia is thrown into vitriol, we have a case of simple affinity, with a complete change, also, of properties. Both the vitriol and magnesia are eminently hurtful to life. All their elements combine, without any disengagement, and the result is the production of Epsom salts, a compound with properties entirely new. Neither ingredient has been destroyed; they can again be extracted pure from the compound; but they have changed their characters through the force of affinity. But if a piece of glass, quartz, or gold, be thrown into the acid, no change is produced in either, because their particles have no affinity. This process is termed in chemical language combination. It is quite distinct from aggregation, which is the union of particles of a similar kind, forming a mass which has the general properties of the particles of which it is composed, whatever may be its structure or form. It is also to be distinguished from mixture, in which the particles, although they may be intimately blended, are not as it were amalgamated with each other so as to lose their own individual properties. The difference between combination and mixture will be clearly seen from the following example:-If into a crystal bottle we pour a quantity of oil and a quantity of water, and shake them well together, the two substances can never be made to unite permanently together. Although they appear to do so for a short while after the experiment is made, yet if the vessel be allowed to stand for a sufficient length of time, the particles of water, being heavier than those of oil, will descend to the bottom, whilst those of the oil will settle upon the top. Here it is evident that no chemical attraction has been exerted between the particles of the two bodies, because no chemical change has taken place. In a word, there has been a mechanical mixture without any chemical combination. But if with the water in this experiment we mix a quantity of potash, so as to form a pretty strong solution, the results will be very different. The particles of the bodies will intimately combine with each other, and a compound will be formed having properties entirely different from either the oil or the potash. The substance thus obtained is the useful article soap; and if the water be evaporated by the application of heat, it assumes a solid consistency, as in the form in which it is commonly used for domestic purposes. It sometimes happens that two bodies will readily combine with each other, but if a third body be added the combination will be destroyed; the first of the two bodies having a stronger affinity for the third than it had for the second. Thus, if magnesia be dissolved in nitric acid, a complete union takes place; but if lime be added to the compound, the nitric acid unites with the lime, and the magnesia, which was formerly invisible, will fall to the bottom of the vessel. Sulphur and quicksilver, when heated together, will form a beautiful red compound, known under the name of vermilion, and which has none of the qualities either of sulphur or quicksilver. Suspend a piece of aqueous sulphate of copper (common blue vitriol), by a thread, in a glassful of water. The particles of both combine and form a stream of blue fluid, which descends from the points where they are in contact. The solid is said to be dissolved, that is, the cohesion of its particles is destroyed, and the compound is called a solution of the solid. The restoration of cohesion to a body after it has been deprived of it, is exhibited in a great variety of instances. For example, if a quantity of sugar be dissolved in water, and the solution be allowed to stand till the water has evaporated, the attraction of cohesion will take effect between the particles of the sugar, which will again resume the solid form. Here, however, a remarkable circumstance has occurred. Whatever the state of the sugar may have been originally, it invariably, in resuming its solidity, assumes a particular form, one of great regularity and beauty. It was formerly opaque, it is now transparent; originally a shapeless mass, it is now a prism of six sides, surpassing in lustre and symmetry the products of the lapidary's wheel. This solid spontaneous production is called a crystal; and the process by which it is produced is entitled Crystallisation.-Bodies, whether solid, fluid, or vaporous, are susceptible of assuming the crystalline form, and the substances which do so are numberless. The shapes which the crystals take, and the facility with which they assume them, are various. Instances of crystallisation, such as sea-salt, Epsom salts, saltpetre, are familiar to every one. Water, it is well known, when cooled to a certain degree, assumes the form of ice, which is crystalline. There are three methods of producing artificial crystals: first, by dissolving the substance in a hot liquid, and either allow ing the solution to cool, or evaporating it by continued heat; second, by making the substance assume the aerial form; and, third, by melting it by fire without the presence of a liquid, and allowing it to cool slowly. The two first are the most common methods of forming crystals, and by the third, sulphur, spermaceti, bismuth, &c., may be made to assume the crystalline state. If as much alum be put into boiling water as the water will readily dissolve, crystals will be deposited as soon as the liquid cools. The presence of the atmosphere has considerable influence upon the formation of crystals. If as great a quantity of Glauber salt be dissolved in a flask half filled with boiling water as the water will hold solation, and the flask be corked, no crystals will be formed as the liquid cools. Remove the cork, however, and crystallisation commences as the air enters, a solid crystalline mass being almost instantaneously formed. If the weather is warm, crystallisation will not perhaps take place even after the solution is cool. In this case, the introduction of a small crystal into the flask will cause the liquid to crystallise. The same body does not invariably exhibit the same form of crystals; there may be several forms of crystals belonging to one body, but in one or other of these it is sure to crystallise, and not according to any other form. It is also to be observed, that very different kinds of matter may crystallise after the same model. The general name for the substance formed by chemical attraction is a compound; the substances of which it is composed are called its component or constituent parts or principles. The separation of these is termed decomposition; and when decomposition is performed for the purpose of ascertaining the composition of a body, it is named chemical analysis. The reunion of the constituent parts is denominated chemical synthesis. Integrant particles of a body differ from the constituent particles thus :-The latter are the most minute parts into which a compound body can be resolved by decomposition, and are hence of a different nature, both with regard to each other and the substance itself which their mutual union gives rise to. The integrant par ticles are the most minute parts into which any body can be resolved without decomposition. LAWS OF CHEMICAL COMBINATION AND DECOMPOSITION. There are various laws connected with, and phenomena attendant upon, chemical attraction. While, of course, it can operate only between bodies of a different nature, the qualities which characterise these bodies when separate are changed or annihilated by their com bination, and it takes place only between the atoms or most minute particles of bodies. Chemical attraction can take place between two, three, or even a greater num ber of bodies. A change of temperature is almost always observable at the moment of combination. The force of chemical affinity between the constituents of a body, is estimated by that which is requisite for their separation. It has been already remarked that the degree of attraction varies very considerably in different bodies; and it is evident that from this variation all chemical compositions and decompositions take place. The preference of uniting with another substance which any given body is found to exercise, is metaphorically termed elective attraction, or affinity. It is of two kinds, each of which derives its appellation from the number and the powers of the principles which may be brought into contact with each other. When a simple substance is presented to a compound one, and unites with one of the constituents of the latter, so as to separate it from that with which it is combined, and by this means producing a decomposition, it is said to be effected by simple elective attraction. Some substances, however, will not be thus easily decomposed; and it is found necessary to introduce two or more principles, in order to effect the end in view. When two principles, therefore, are presented to a compound body, and when the principles unite each with one of those of the compound substance, two new substances are formed; and all instances of decomposition in this manner are said to be effected by double elective attrac tion. It is to be observed, that all changes effected in this manner are permanent, and that the new compound thus formed cannot be decomposed, until a substance having a more powerful attraction for one of its constituents than they have for each other, is brought into contact with them. To Sir Isaac Newton we are indebted for the first attempt at a rational explanation of chemical combination. He was of opinion that the minute atoms of certain bodies attract each other with an unknown but enormous force, which begins to exert itself only when the particles are at very small distances from each other, and that, accordingly, this force exerts itself, and the bodies unite, when they are brought within the requisite distance. These views slowly made their way into the science; but towards the middle of the eighteenth century, they seem to have been almost universally adopted. The term chemical affinity was substituted for that of attraction, and the strength of the affinity existing in bodies came to be measured according to the order in which they were decomposed. It is unnecessary to mention the various tables of affinity which were published previously to that of Bergman, who in 1775 gave to the world a copious table of affinities, and appears to have fixed the opinions of chemists in general to his own views of the subject. According to this philosopher, the affinity of each of the bodies, say a, b, c, d, for a, differs in intensity in such a manner, that the degree of affinity in each may be expressed by numbers. He supposed affinity to be elective, in consequence of which, if a have a greater affinity for a than b, if a be presented to the compound b x, a decomposition will ensue, b will be set at liberty, and the compound a r will be formed. THE ATOMIC THEORY. it will be converted into a red shining mass, which is also a compound of the metal with oxygen; but in the latter case, sixteen parts of oxygen have united with the two hundred and two parts of the metal. The explanation of this is, that eight is the chemical equivalent of oxygen, and two hundred and two of mercury. In every successive compound which they make, their proportions form a multiple of these equivalents. Every other simple body has, in like manner, its equivalent number, and to its compounds the same rule applies. Innumerable instances of this might be adduced, but these are sufficient to prove the remarkable truth, that when different substances combine by chemical attraction, the proportions of the ingredients are always uniform; that for every atom present of one substance, there is exactly one, or two, or three, &c., of the other. If, for instance, any quantity of sulphur, intermediate between the two combinations of that substance with mercury, be added, it will not combine with it, but remain as a foreign ingredient in the sulphuret of mercury, as the compound is termed. All bodies, however, do not unite in several proportions, thus giving rise to several distinct compounds from two elements; there are many elementary bodies which will only unite with each other in one proportion, so that any two of such substances can only form one compound. This law, however, is not universal, as it is well known that water and alcohol, and water and sulphuric acid, will unite in any proportions. Water will also unite in any proportion with soluble salt, until it becomes completely saturated. Bodies which unite in any proportions form an infinite variety of compounds, and are distinguished by their being united by a weak affinity, and also by the compounds formed differing little from their simple con This theory was not discovered all at once, and immediately acknowledged by chemists; it was gradually brought to light by the repeated experiments of successive philosophers, whose labours, however, it will be impossible to exhibit a view of in this place. To Mr Dalton we are indebted for the first development and demonstration of the fact, that bodies unite in definite proportions; and of which we shall now attempt to present the reader with as clear and simple a view as possible. Whilst engaged in determining the composition of the two gases called severally carbureted hy-stituents or from each other. drogen and olefiant gas, Mr Dalton discovered that for complete combustion they require different but determinate quantities of oxygen gas. A volume* of carbureted hydrogen requires two volumes, whilst a volume of olefiant gas requires three volumes of oxygen gas. The conclusions at which Mr Dalton arrived are, that bodies consist of atoms incapable of further diminution or division; that in chemical combinations it is these ultimate particles which unite; and that, in the case above mentioned of the combustion of the two inflammable gases, carbureted hydrogen is a compound of one atom of hydrogen and one atom of carbon; whilst olefiant gas is a compound of one atom of hydrogen and two atoms of carbon. The atoms he considered as spheres, and represented them by such symbols as a circle with a dot in the centre, a circle with a vertical diameter, and the like. In this manner the composition of a number of the best known bodies was represented by him, and the ratios of the weights of the atoms of the simple bodies inferred. For instance, he concluded from his experiments that carbureted hydrogen is composed of, hydrogen one, and carbon five; while olefiant gas is composed of, hydrogen one, and carbon ten. Now, as the former gas consists of one atom of hydrogen and one atom of carbon, then the weights of these atoms are to each other in the relation of one to five. If the weight of the atom of hydrogen, therefore, be represented by one, that of carbon will be five. In this manner, the ratios of the weight of the atoms of all the simple bodies may be ascertained by a careful analysis of the compounds formed by the union of the simple bodies. The combinations of mercury or quicksilver with some other bodies, afford an illustration of the theory. Its first compound with oxygen, one of the gases of which the atmosphere is composed, consists of two hundred and two parts of mercury and eight of oxygen. If, however, the metal be subjected to a considerable degree of heat, * Volume, în chemistry, is a term employed to denote any quan. tity in bulk of a substance. It is usually applied to the gases. Thus, one volume of hydrogen gas is, say, a cubic foot, yard, or any other quantity; then two volumes are of course just double Le cubic foot, yard, or whatever other quantity was previously mentioned. These remarks must be held as applying to inorganic chemistry chiefly; vegetable, or organic chemistry, presents many exceptions to the principles of combination now laid down. EQUIVALENT RATIOS. The result of these investigations has been the formation of scales exhibiting the equivalent ratios of chemical bodies, and which are expressed by numbers. It is evident that some body must be fixed upon, and expressed by unity. Hydrogen gas, being the lightest known body in nature, and combining in the smallest proportion by weight with the other simple substances, has been taken as a standard of comparison for the combining proportions, or equivalent numbers, of all other bodies; and which, in all likelihood, are simple multiples of its number. Oxygen has also, by some chemists, been taken as the standard of comparison, and represented by ten. Water is a compound of eight parts by weight of oxygen, with one part by weight of hydrogen; which two gaseous bodies we shall afterwards describe. Whenever hydrogen and oxygen gases are burnt in any proportion whatsoever, they invariably form water; and they cannot be made to combine directly in any other proportion. From this, Dalton concluded that water is a compound of one atom of hydrogen and one atom of oxygen. But the weight of the latter gas being eight times that of the former, then it followed that the atom of oxygen was just eight times heavier than the atom of hydrogen. Hence, if the latter be represented by one, then will the former be represented by eight, according to those who take hydrogen as the standard. Those who take oxygen as the standard, and represent it by 10, make the equivalent for hydrogen 125: the result is of course the same, the proportion of 1·25 to 10, being exactly the same as that of 1 to 8. These observations relative to water lead us to speak of the doctrine of volumes, so generally embraced by chemists upon the Continent. The union of gases is always effected in simple proportions of their volumes; and a volume of one gas combines with an equal volume, or twice or three times the volume, of another gas; and in no intermediate proportion. |