= 8

Hydrogen 1 atom = 1
Oxygen
Water

1 atom

1 atom = 9

The weight, then, of a compound atom is obtained by adding together the atomic weights of its constituents. Although may elementary bodies unite with hydrogen, there are some which do not, but there is no one which does not combine either with hydrogen or with oxygen when, therefore, the hydrogen standard or unit fails on this account, we may refer to the atom of oxygen, and determine what weight of the substance in question, supposing only one compound to be formed, unites with eight parts by weight, or one atom of oxygen. Now cadmium is a metal of this description; it forms no compound with hydrogen, and only one with oxygen, and as eight parts of this element unite with fifty-six of the metal, to form the only known oxide of it, we say that the atomic weight of cadmium is fifty-six, and that the oxide is composed of

It is, however, possible, though by no means probable, that such an inference may be incorrect, for the oxide in question may be composed either of two or more atoms of oxygen united with one atom of the metal, or the contrary, instead of what it is presumed to be; but the error may be detected by examining the proportion in which the metal unites with other elements, whose atomic weights are already determined. The atomic weights of sulphur, chlorine, and selenium, are respectively 16, 36, and 40: now if, in a series of combinations with these substances, the compounds containing the largest proportion of metal were

constituted of

Sulphur 16

Chlorine 36 Metal 56 Metal

Selenium 40 56 Metal 56

we should conclude that the atomic weight of the metal was 112, and consequently that the oxide formed of 8 oxygen and 56 metal, was a peroxide, equivalent to 16=2 atoms of oxygen + 112=1 atom of metal.

If, on the other hand, it appeared that the compound containing the largest proportion of metal consisted of

Sulphur 16 Chlorine 36 Selenium 40 Metal 28 Metal 28 Metal 28 we must then consider the oxide composed of 8 oxygen and 56 metal as a suboxide, constituted of 1 atom of oxygen-8 +2 atoms of metal = 56.

This method of proceeding is according to the rule thus laid down by Dr. Dalton: It is necessary not only to consider the combinations of A with B, but also those of A with CD E, &c., as well as those of B with C D, &c., before we can have good reason to be satisfied with our determination as to the number of atoms which enter into the various compounds. (New System of Chemical Philosophy, vol. ii. p. 300.)

In fact, the protoxide of a metal, i. e. 1 atom oxygen + 1 atom metal, may possess such properties as to prevent its composition from being by direct means accurately ascertained; and it is likewise possible that no protoxide may exist.

We have alluded to the circumstance, that various compounds of the same two elements may exist, and supposing an elementary body, as copper or silver, united with two proportions of oxygen, various questions may arise as to the constitution of the resulting oxides: as, whether that which contains least oxygen is a suboxide or protoxide; or whether that which contains most is a protoxide or a peroxide. These are points which can be determined only by compari

= 8 =64

Protoxide of cop. 1 atom =72

= 16 =64

Oxygen 2 atoms Copper 1 atom Peroxide of cop. 1 atom=80 This rule of assuming that oxide to be a protoxide which contains least oxygen will be generally found correct, especially when confirmed, as it is in this instance, by the corresponding constitution of the two chlorides and two sulphurets. The oxides of silver, however, form an exception, though a very rare one, to this rule; there are two oxides of this metal composed of and

Oxygen 8

Silver 165

Oxygen 8 Silver 110

If it were to be assumed in this case, that 165 is the atomic weight of silver, because it is the largest proportion which combines with 8, or 1 atom of oxygen, the assumption would be erroneous, for this oxide has no corresponding chloride, sulphuret, &c., and it would be unlike other protoxides, in forming no compound with any acid. But all these properties belong to the oxide of silver composed of 8 oxygen and 110 silver; in this case the oxide containing most metal is considered as a suboxide, composed of 2 atoms oxygen 16+3 atoms silver 330. In general however, the rule may be relied upon, that the metallic oxide which contains least oxygen is the protoxide, and that weight of the metal which combines with 8 by weight of oxygen, denotes the weight of its atom, and their united weight that of the oxide.

It will be observed with respect to the compounds of oxygen and copper, that the second portion of that element which unites with the same quantity of the metal, is double the first. Now upon this and numerous similar facts is founded one of the most important and beautiful peculiarities of Dr. Dalton's theory, sometimes described as the doc trine of multiples. In the case just alluded to, the second portion of oxygen is precisely double the first; but there are some cases in which the greater proportions are not multiples of the less, by any entire number: for example, there are two well-known oxides of iron consisting of

The first of these is the protoxide, and the second the peroxide; but it will be observed, the second portion of oxygen is only one-half greater than the first, instead of double, as happens with respect to copper. In fact, the additional quantity is equal to only half an atom of oxygen; but as the idea of dividing an atom is absurd, the difficulty is overcome by multiplying both the oxygen and iron by 2, in which case we shall have 12 x 2 = 24, or 3 atoms of oxygen, combined with 28 x 2 = 56, 2 atoms of iron, and these proportions are perfectly consistent with the theory. Other cases of apparent anomaly occur: thus there are three oxides of lead, viz.,

The first and last of these oxides are constituted exactly as the oxides of copper are, the second portion of oxygen being double that of the first; but the red oxide of lead is composed of an atom of metal and such a quantity of oxygen as is equal to one atom and a third. If, then, both the oxygen and metal be multiplied by 3, we shall have a compound of 4 atoms of oxygen and 3 atoms of lead, or 32+312=344, and it is found if these 344 parts of red lead be treated with dilute nitric acid, they are separated into 2 atoms of protoxide = 224, which are dissolved, and 1 atom of peroxide = 120, which remains unacted upon in the state of a brown powder. This case, then, of apparent anomaly is explained by showing that the red oxide of lead is equivalent to, or perhaps composed of, the other two oxides, and is resolvable into them.

=

The oxides of manganese offer a still more remarkable case of apparent irregularity of combination, and of the disposition of metallic oxides themselves to combine in definite proportions. There are five oxides of this metal, all of

must also be considered as having one combining weight for their acids and another for their bases.

It may now be easily made to appear how it happens that when two neutral salts decompose each other, the new salts obtained by the operation are also neutral; an atom of nitric acid weighs 54, and one of barytes 76, forming when combined 130 of neutral nitrate of barytes; 88 = an atom of neutral sulphate of potash is composed of an atom of sulphuric acid=40, and an atom of potash =48. Now when 130, or an atom of nitrate of barytes, dissolved in water, is mixed with a solution of 88, or an atom, of sulphate of potash, double decomposition ensues, and two new and perfectly neutral salts are formed, viz., 1 atom of nitrate of potash = 102, consisting of an atom of nitric acid = 54, and an atom of potash 48; this remains in solution; and there is precipitated an atom of neutral sulphate of barytes = 116, composed of 1 atom of sulphuric acid = 40, and 1 atom of barytes = 76. The annexed diagram will show the constitution of the salts employed, and those formed by their mutual decomposition; and it will be seen also that the weight of the new compounds is precisely equal to those of the original salts.

14 3

With respect to azote also, the atomic weight is fixed at 14, that being the largest quantity which combines with 8 of oxygen. There is only one compound of hydrogen and azote, viz., ammonia; this consists of 3 parts by weight of hydrogen and 14 by weight of azote; consequently, if we had taken the hydrogen standard, the atomic weight of azote would have been =4'66, which would have greatly complicated the constitution of the compounds of oxygen and azote; but the alternative of supposing ammonia to contain 3 atoms of hydrogen instead of 1 atom is of secondary importance, though it must be admitted that it contravenes the rule laid down by Dr. Dalton, that when only one combination of two bodies can be obtained, it must be presumed to be a binary one.'

The case in which the second portion of oxygen in an oxide, instead of being equal to the first, is only one-half greater, has been pointed out in the instance of the oxides of iron, and the means by which the absurdity of supposing

the existence of half an atom is obviated have been mentioned. There are, however, some cases, in which it is convenient to consider such an oxide as containing an atom and a half of oxygen, and it is then termed a sesquioxide; there are also several instances in which salts are commonly considered as containing a quantity of acid equal to an atom and a half, and these are termed sesquisalts. The alkalies ammonia, potash, and soda, and some other bases, form three compounds with the same acid: for example, we have Carbonate of potash, composed of 1 atom acid+1 atom base Bicarbonate of potash, 2 atoms acid + 1 atom do.

and a carbonate of potash, 3 atoms acid +2 atoms do. It is then evident that the last salt is equivalent to a compound of 14 atom acid +1 atom base. Now if an atom of this salt, considered as a sesquisalt, be added to an atom of nitrate of lime, double decomposition ensues, 1 atom of neutral nitrate of potash remains in solution, 1 atom of neutral carbonate of lime is precipitated, and carbonic acid equal to half an atom is expelled in the state of gas. With respect to its base then, sesquicarbonate of potash may be regarded as a neutral carbonate, though, as to its acid, as a sesquicarbonate; for if lime-water be added to an atom of a sesquicarbonate, carbonate of lime is precipitated equivalent in quantity to 1 atom.

These facts are sufficient to shew that combining and atomic weights are not convertible terms, though they have been so employed. Thus the atomic weight of an anhydrous compound of 3 atoms carbonic acid and 2 atoms potash, is 162: considered as a sesquicarbonate, its atomic weight is 81; and its combining weight is the same with respect to an atom of nitric acid; but it is one-half greater as regards an atom of lime. The same remark will apply to bisalts; they

No. 141.

130

of

Barytes.

Although the atomic theory, thus developed by Dr. Dalton in 1808, contained truths of the highest importance, quite independent of the hypothesis by which they were illustrated, it was not until after the appearance of Dr. Wollaston's Memoirs, On Super-acid and Sub-acid Salts, and On a Synoptic Scale of Chemical Equivalents, that chemists were fully impressed with the practical applications of which the theory was susceptible. In the first memoir (Phil. Trans. 1808), a memoir equally remarkable for its conciseness and clearness, Dr. Wollaston shows, that Dr. Dalton's theory, first applied to determining the constitution of gaseous bodies, is applicable to that of super-acid and contains exactly half the quantity of carbonic acid existing sub-acid salts; and he proves that sub-carbonate of potash in the super-carbonate, by showing that if the latter be heated it loses half its acid, and is reduced to the state of sub-carbonate by the loss; the same rule was found to exist with the sub-carbonate and super-carbonate of soda, the sulphate and super-sulphate of potash, and with three oxalates of potash.

The paper on the synoptic scale appeared in the Phil. Trans. for 1814. By this instrument the practical utility of the doctrine of definite proportions was most satisfactorily pointed out.

This instrument consists of a moveable scale of num

bers on the principle of Gunter's scale, so that any number can be placed opposite the names of a series of substances in adjoining columns, arranged in the order of their combining weights, in such a manner that the number denoting the combining weight of a body being placed opposite to its name-10, for example, opposite to oxygen-the numbers expressing the combining quantities of others will appear opposite to their names; thus copper will be found opposite to 40, showing that this quantity of it combines with 10 of oxygen, and opposite to 50 will be found oxide of copper. By mere inspection, a great number of important results are obtained. If the composition of a substance with regard to the proportion of its elements is to be determined, the slider is to be so placed that the number 100, or any required number, is opposite to its name, and the respective quantities of the ingredients will be found opposite to their names, and the quantities of other compounds required to decompose them: for example, when 86 is placed opposite to sub-carbonate of potash, 275 will be opposite to carbonic acid, 591 to potash, 613 to oil of vitriol, 50 to dry sulphuric acid, and 113 to water.—

Dr. Wollaston, equivalent, oxygen 10 hydrogen 1:32 proportion, hydrogen 2 oxygen

Sir H. Davy, Dr. Thomson, Berzelius,

Dr. Henry,

Dr. Turner,

15

Vanadium

855.840 68.578

8

8

8

atom, oxygen 1 hydrogen 1.25 atom, oxygen 100 hydrogen 12:4795 atom, hydrogen 1 oxygen 8 equivalent, hydrogen 1 oxygen Mr. Faraday, proportional, hydrogen 1 oxygen Mr. Brande, proportional, hydrogen 1 oxygen The method of mutually converting the numbers of each standard into those of the other is too obvious to require explanation. The use of the term atom has been objected to as hypothetical, because it is said that we have no means of ascertaining or judging of the weight or magnitude of an atom of any element, and that any supposed relative weight of their atoms must therefore be a mere hypothetical assumption, from which no satisfactory conclusion can be drawn; and by those who appear to entertain this opinion, other terms, as above quoted, are substituted for the word atom, which is, however, intended to express merely the smallest division which is found of any element without decompo

sition.

The following remarks by Dr. Wollaston, in his memoir on the finite extent of the atmosphere (Phil. Trans. 1822), are strongly in favour of the atomic constitution of matter. 'Now, though we have not the means of ascertaining the extent of our own atmosphere, those of other planetary bodies are nevertheless objects for astronomical investigation; and it may be deserving of consideration, whether, in any instance, a deficiency of such matter can be proved, and whether, from this source, any conclusive argument can be drawn in favour of ultimate atoms of matter in general. For, since the law of definite proportions discovered by chemists is the same for all kinds of matter, whether solid, or fluid, or elastic, if it can be ascertained that any one body consists of particles no longer divisible, we can then scarcely doubt that all other bodies are similarly constituted; and we may without hesitation conclude, that those equivalent quantities, which we have learned to appreciate by proportionate numbers, do really express the relative weights of elementary atoms, the ultimate objects of chemical research.'

Table of the Atomic Weights of Elementary Bodies.

Platinum Iridiuin Mercury Gold Tungsten Osmium Lead Silver Iodine Columbium Uranium

It is to be observed, that it is not ponderable matter only which appears to obey the law of definite proportions; Dulong and Petit have inferred from their experiments (An. de Ch. et de Ph., vol. x.) that the atoms of simple substances have the same capacity for heat. Dr. Dalton has, however, objected to this opinion, that the product of the weight of an atom by the corresponding capacity for heat is not a constant quantity; because the capacity of the same substance varies with change of form, or with variation of temperature without change of form. Added to which the weights of the atoms, as indicated by the specific heat, would be very materially different from those now adopted in many cases.

The late beautiful experiments of Mr. Faraday on the absolute quantity of electricity associated with the particles or atoms of matter, prove that, for a given definite quantity of electricity passed, an equally definite and constant quantity of water or other matter is decomposed; and he concludes also, that the electricity which decomposes, and that which is evolved by the decomposition of, a certain quantity of matter, are alike. The harmony,' he observes, which this theory of the definite evolution and the equivalent definite action of electricity introduces into the associated theories of definite proportions and electro-chemical affinity, is very great. According to it, the equivalent weights of bodies are simply those quantities of them which contain equal quantities of electricity, or have naturally equal electric powers; it being the electricity which determines the equivalent number, because it determines the combining force. Or, if we adopt the atomic theory or phraseology then the atoms of bodies which are equivalents to each other in their ordinary chemical action have equal quantities of electricity naturally associated with them.' (Phil. Trans. 1834.)

With respect to the utility of the atomic theory, we cannot do better, in concluding this account of it, than to state, in the words of Dr. Daubeny (Introduction to the Atomic Theory, p. 87), that 'it would be superfluous to enlarge upon the proofs already afforded, with respect to the greater precision it has introduced into the science,-the wonderful saving of time and labour which is derived from it, not only by the philosopher in his more speculative inquiries, but even by the manufacturing chemist, in the every-day operations of his trade.'

It is evident that, in the present state of our knowledge, no sooner have we ascertained the exact proportion in which a new substance unites with any one of those bodies whose atomic weight is already determined, than we are enabled to calculate in what quantities it must combine with all the remainder, so that, instead of being compelled, as heretofore would have appeared necessary, to analyze every existing combination, in order to determine the proportion of its ingredients, we might rest contented, were it not for the sake of obviating the chances of error in any single ex periment, with ascertaining the composition of one out of

the whole number of compounds, into which the ingredient in question enters.

ATONEMENT, a certain mode of appeasing anger, and obtaining pardon for an offence. In the act of atonement there is commonly understood to be a substitution of something offered, or of some personal suffering, for a penalty which would otherwise be exacted. The word is, indeed, applied colloquially to any circumstance of suffering, voluntary or involuntary, consequent upon criminal conduct or error of judgment. Thus even the spendthrift is said to have atoned for his folly by the hardships endured in consequence of it, and the murderer for his crime by a public death. But this use of the word is altogether indefensible. In theology, it has respect to offence committed against the Deity; it is in the theological acceptation of the term that it will be considered in the present article. The subject in this view of it is partly connected with that of sacrifice [see SACRIFICE]; but it is not identical with it. For it is not certain that all sacrifices had atonement for their object; and sacrifice, as commonly understood, was only one amongst other methods of atonement.

The practice of atonement is remarkable for its antiquity and universality, proved by the earliest records that have come down to us of all nations, and by the testimony of antient and modern travellers. In the oldest books of the Hebrew Scriptures, without noticing those earlier sacrifices the object of which may be considered doubtful, we have numerous instances of expiatory rites where atonement is the prominent feature, occupying, in fact, a large portion of the four last books of the Pentateuch. In some cases the atonement was made for a specific offence (Levit. iv., Numb. xvi. 46); in others it had reference to a state of transgression, as especially in the case of the scape-goat, on the day of expiation. (Levit. xvi.) The offender again either atoned by his own personal act, or received the benefit of atonement by the act of another. (Levit. iv.) The Hebrew records contain also notices of the practice of atonement, independent of the Mosaic institutions, and unconnected with the religious opinions of the Hebrew people. The barbarous offerings to Moloch appear in the light of atonements when interpreted by the indignant expostulation of Micah (vi. 7) Shall I give my first-born for my transgression, and the fruit of my body for the sin of my soul? When Job is described (i. 5) as offering burnt offerings according to the number of his sons, and accompanying the act with the explanation, ‘It may be that my sons have sinned, and cursed God in their heart,' we are sure that the author of the book, and those for whom he wrote, were familiar with the notion of atonement. The name, indeed, and the age of the writer, are both disputed points; but there are strong reasons for attributing to the work a very high antiquity.

Át the earliest date to which we can carry our inquiries by means of the heathen records, we meet with the same notion of atonement, with a distinction also in the application, between the removal of anger incurred by particular offences, and of that which was supposed to belong to the jealous character of the Deity. An instance of atonement of the former kind meets us in the very opening of the Iliad. Agamemnon having offended Apollo in the person of his priest, by refusing a ransom for his daughter, is not content with restitution, but proceeds to atone for his fault by an offering, the purpose of which is declared by Ulysses (Il. i. 442)-Agamemnon sent me to sacrifice a sacred hecatomb to Apollo in behalf of the Danai, that we may appease the Sovereign God."

Among the many other instances which will readily occur to a reader of the antient classics, the sacrifice of Iphigeneia by her father, to appease the wrath of Diana, is distinguished by the remarkable circumstance of the substitution of one victim for another by the offended goddess. It should be observed, however, that although the subject of the legend belongs to the period of the Trojan war, the legend itself is of a later date than the Homeric poems. In the expiatory rites for certain cases of homicide, sacrificial offerings to the Deity formed a part of the religious ceremony of purification, in addition to the penalty which the offender paid as a compensation to the avenging party. A singular instance of atonement made to the Diana Orthia of the Lacedæmonians is given by Pausanias (iii. 16). Blood having been shed in a quarrel during a solemn sacrifice to the goddess, human victims were regularly offered to her as an atonement for the offence; till Lycurgus substituted for

this cruel ceremony the scourging of youths at the altar with such severity, that the penalty was still paid with blood. The practice of general atonement among the heathen nations, whatever may have been its origin, must have been greatly encouraged by a certain article in the popular creed, which is probably expressed pretty accurately by the saying put into the mouth of Solon by Herodotus, that the Deity is altogether a jealous being, and fond of troubling the even course of affairs' (plovεpòv Tε kai rapax@des, Herod. i. 32). The common notion is remarkably exemplified in a story told by the same historian. Amasis, king of Egypt, having heard rumours of the marvellous and uninterrupted successes of his friend Polycrates, the sovereign of Samos, gave vent to his anxiety on his friend's account in a letter, which is in itself so curious, and so strongly illustrates the matter in hand, that we think it deserves to be presented entire to the reader. 'Amasis`says thus to Polycrates -It is pleasant to hear that one's friend prospers; yet your exceeding good fortunes please me not, knowing as I do that the Deity is a jealous being; and I could wish that both myself and those whom I care for should be fortunate in some of their doings, and in others miscarry; and so pass their lives in changes of fortune, rather than be always fortunate; for I never yet heard talk of any one who with good fortune in everything did not come to his end miserably with an utter downfall. Do you therefore follow my advice, and in respect of your happy chances do as I tell you. Look out well for the most precious thing you have, and that which you would most take to heart the loss of and then away witn it, in such sort that it shall never more come before the eyes of men. And if after this your successes should not take turns and go evenly with your mishaps, still remedy the matter in the way proposed by me.' (Herod. iii. 40.) The story goes on to say that Polycrates took the advice of his friend, and flung into the sea a valuable ring; but the object was defeated by an incredible piece of good fortune, which restored to him his lost treasure. Hereupon Amasis formally dissolved his connexion with a man so evidently marked out for some signal calamity.

In this case the offence was involuntary; yet it was not the less supposed to excite anger and expose the offender to punishment. Here too is an instance of atonement unaccompanied by sacrifice. The mode, indeed, of atoning admitted an almost infinite variety. Even the repetition on a certain occasion of the great games at Rome was strictly an act of atonement for a rather singular offence described by Livy, lib. ii. c. 36.

If we pursue our inquiries through the accounts left us by the Greek and Roman writers of the barbarous nations with which they were acquainted, from India to Britain, we shall find the same notion and similar practices of atonement. From the most popular portion of our own literature, our narratives of voyages and travels, every one probably, who reads at all, will be able to find for himself abundant proof that the notion has been as permanent as it is universal. It shows itself among the various tribes of Africa, the islanders of the South Seas, and even that most peculiar race, the natives of Australia, either in the shape of some offering, or some mutilation of the person. We should expect to meet with it in India, so fertile in every form of superstition; and it is certain that many of the fantastic and revolting rites of the Hindoos bear testimony to its presence. The favourite practice of torturing the body has often there a different object, that of acquiring the reality or the fame of superior sanctity; but undoubtedly it is also resorted to as a mode of atonement.

It has been supposed that the sacrificial rites of the heathens and their practice generally of atonement are but corrupt remnants of a notion and practice which existed at an earlier period of the world, in a purer state of religious knowledge, and which indicated a consciousness of the actual relation in which man stood to his Maker, and pointed darkly at the means by which an amelioration of his condition was to be effected. On the other hand, it is all but universally acknowledged by the believers in revelation, that the Levitical atonements were, in part at least, typical of that one great sacrifice on which the Christian doctrine of the atonement is founded. The nature and limits of this publication do not allow us to consider this part of the subject at a length and in a manner suited to its importance. We can do little more than state what is understood by the Christian when he speaks of the atonement. He does not consider man, according to the heathen notion