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ELEMENT (Lat. elementum)

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Originally appearing in Volume V09, Page 259 of the 1911 Encyclopedia Britannica.
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ELEMENT (See also:Lat. elementum) , an ultimate component of any-thing, hence a fundamental principle. Elementum was used in Latin to translate the See also:Greek vrotxe ov (that which stands in a vroixos, or See also:row), and is a word of obscure origin and See also:etymology. The See also:root of Lat. alere, to nourish, has been suggested, thus making it a doublet of alimentum, that which sup-ports See also:life; another explanation is that the word represents LMMIN., the first three letters of the second See also:part of the See also:alphabet, a parallel use to that of See also:ABC. Apart from its application in See also:chemistry, which is treated below, the word is used of the rudiments or principia of any See also:science or subject, as in See also:Euclid's Elements of See also:Geometry, or in the " beggarly elements " (ra r rwxa aroLxsLa, of St See also:Paul in Gal. iv. 9) ; in See also:mathematics, of a fundamental concept involved in an investigation, as the elements " of a See also:determinant; and in See also:electricity, of a galvanic (or voltaic) " element " in an electric See also:cell (see See also:BATTERY: Electric). In See also:astronomy, " element " is used of any one of the numerical or geometrical data by which the course of a varying phenomenon is computed; it is applied especially to orbital See also:motion and eclipses. The " elements of an See also:orbit " are the six data by which the position of a moving See also:body in its orbit at any See also:time may be determined. The " elements of an See also:eclipse " See also:express and determine the motion of the centre of the See also:shadow-See also:axis, and are the data necessary to compute the phenomena of an eclipse during its whole course, as seen at any See also:place. In See also:architecture the See also:term " element " is applied to the outline of the See also:design of a Decorated window, on which the centres for the See also:tracery are found. These centres will all be found to fall on points which, in some way or other, will be equimultiples of parts of the openings. Chemical Elements. Like all other scientific concepts, that of an element has changed its meaning many times in many ways during the development of science.

Owing to their very small See also:

Ancient amount of real chemical knowledge, the generalizations ideas. of the ancients were necessarily rather superficial, and could not stand in the See also:face of the increasing development of See also:practical chemistry. Nevertheless we find the concept of an element as " a substance from which all bodies are made or derived " held at the very beginning of occidental See also:philosophy. Thales regarded " See also:water " as the element of all things; his253 followers accepted his. See also:idea of a primordial substance as the basis of all_ bodies, but they endeavoured to determine some other See also:general element or elements, like " See also:fire " or " spirit, " or "love" and hatred," or " fire," " water," " See also:air " and " See also:earth." We find in this development an exact See also:parallelism to the manner in which scientific ideas generally arise, develop and See also:change. They are created to point out the See also:common part in a variety of observed phenomena, in See also:order to get some leading See also:light in the See also:chaos of events. At first almost any idea will do, if only it promises some comprehensive arrangement of the facts; after-wards, the inconsistencies of the first trial make themselves See also:felt; the first idea is then changed to meet better the new requirements. For a shorter or longer time the facts and ideas may remain in See also:accord, but the uninterrupted increase of empirical knowledge involves sooner or later new fundamental alterations of the general idea, and in this way there is a never-ceasing See also:process of See also:adaptation of the ideas to the facts. As facts are unchangeable by themselves, the adaptation can be only one-sided; the ideas are compelled to change according to the facts. We must therefore educate ourselves to regard the ideas or theories as the changing part of science, and keep ourselves ready to accept even the most fundamental revision of current theories. The first step in the development of the idea of elements was to recognize that a single principle would not prove sufficient to See also:cover the manifoldness of facts. See also:Empedocles therefore conceived a See also:double or binary elementary principle; and See also:Aristotle See also:developed this idea a See also:stage further, stating two sets of binary antagonistic principles, namely " dry-wet " and " hot-See also:cold." The Aristotelian or peripatetic elements, which played such a See also:great role in the whole See also:medieval philosophy, are the representative's of the several binary combinations of these fundamental properties, " fire " being hot and dry, " air " hot and wet, " water" cold and wet, " earth cold and dry. According to the amount of these properties found in any body, these elements were regarded as having taken part in forming this body.

Concerning the See also:

reason why only these properties were regarded as fundamental, we know nothing. They seem to be taken at See also:random rather than carefully selected; they relate only to the sense of See also:touch, and not to See also:vision or any other sense, possibly because deceptions in the sense of touch were regarded as non-existent, while the other senses were apparently not so trustworthy. At any See also:rate, the Aristotelian elements soon proved to be rather inadequate to meet the requirements of the increasing chemical knowledge; other properties had therefore to be selected to represent the general behaviour of chemical substances, and in this See also:case we find them already much more " chemical " in the See also:modern sense. Among the various substances recognized by the chemists, certain classes or See also:groups readily distinguished themselves. First the metals, by their lustre, their heaviness, and Elements a number of other common properties. According to of the the general principle of selecting a single substance See also:anthem-as a representative of the See also:group, the metallic properties tats' were represented by " See also:mercury." The theoreticians of the See also:middle ages were rather careful to point out that common mercury (the liquid See also:metal of to-See also:day) was not at all to be identified with " philosophical " mercury, the last being simply the principle of metallic behaviour. In the same way combustibility was represented by " See also:sulphur," solubility by " See also:salt," and occasionally the chemically indifferent or refractory See also:character by " earth." According to the subsistence and preponderance of these properties in different bodies, these were regarded as containing the corresponding elements; conversely, just as experience teaches the chemist every day that by proper treatment the properties of given bodies may be changed in the most various ways, the observed changes of properties were ascribed to the gain or loss of the corresponding elements. According to this theory, which accounted rather well for a large number of facts, there was no fundamental objection against trying to endow See also:base metals with the properties of the See also:precious ones; to make artificial See also:gold was a task quite similar to the modern problem of, e.g. making artificial See also:quinine. The realization that there .is a certain natural See also:law preventing such changes is of much later date. It is therefore quite unjust to consider the See also:work of the alchemists, who tried to make artificial gold, as consummate nonsense. A priori there was no reason why a change from See also:lead to gold should be less possible than a change from See also:iron to See also:rust; indeed there is no a priori reason against it now. But experience has taught us that lead and gold are chemical elements in the modern sense, and that there is a general experimental law that elements are not transformable one into another.

So experience taught the alchemists irresistibly that in spite of the manifoldness of chemical changes it is not always possible to change any given substance into another; the possibilities are much more limited, and there is only a certain range of substances to be obtained from a given one. The impossibility of transforming lead or See also:

copper into See also:noble metals proved to be only one case out of many, and it was recognized generally that there are certain chemical families whose members are related to one another by their mutual transform-ability, while it is impossible to See also:bridge the boundaries separating these families. The See also:man who brought all these experiences and considerations into scientific See also:form was See also:Robert See also:Boyle. He stated as a general principle, that only tangible and ponderable substances work of should be recognized as elements, an element being Robert Boyle. a substance from which other substances maybemade, B but which cannot be separated into different substances. He showed that neither the peripatetic nor the alchemistic elements satisfied this See also:definition. But he was more of a See also:critical than of a synthetical turn of mind; although he established the correct principles, he hesitated to point out what substances, among those known at his time, were to be considered as elements. He only paved the way to the See also:goal by laying the See also:foundations of See also:analytical chemistry, i.e. by teaching how to characterize and to distinguish different chemical individuals. Further, by adopting and developing the corpuscular See also:hypothesis of the constitution of the ponderable substances, he foreshadowed, in a way, the law of the conservation of the elements, viz, that no element can be changed into another element; and he considered the See also:compound substances to be made up from small particles or corpuscles of their elements, the latter retaining their essence in all combinations. This hypothesis accounts for the fact that only a limited number of other substances can be made from a givenone—namely, only those which contain the elements See also:present in the given substance. But it is characteristic of Boyle's critical mind that he did not shut his eyes against a serious objection to his hypothesis. If the compound substance is made up of parts of the elements, one would expect that the properties of the compound substance would prove to be the sum of the properties of the elements. But this is not the case, and chemical compounds show properties which generally differ very consider-ably from those of the compounds.

On the one See also:

hand, the corpuscular hypothesis of Boyle was developed into the atomic hypothesis of See also:Dalton, which was considered at the beginning of the 19th See also:century as the very best See also:representation of chemical facts, while, on the other hand, the difficulty as to the properties of the compounds remained the same as Boyle found it, and has not yet been removed by an appropriate development of the atomic hypothesis. Thus Boyle considered, e.g. the metals as elements. However, it is interesting to See also:note that he considered the mutual transformation of the metals as not altogether See also:im, possible, and he even tells of a case when gold was transformed into base metal. It is a common psychological fact that a reformer does not generally succeed in being wholly consistent in his reforming ideas; there remains invariably some point where he commits exactly the same See also:fault which he set out to abolish. We shall find the same inconsistency also among other chemical reformers. Even earlier than Boyle, See also:Joachim See also:Jung (1587-1657) of See also:Hamburg developed similar ideas. But as he did not distinguish himself, as Boyle did, by experimental work in science, his views exerted only a limited See also:influence amongst his pupils. In the times following Boyle's work we find no remarkable outside development of the theory of elements, but a very important inside one. Analytical chemistry, or the See also:art of distinguishing different chemical substances, was rapidly developing, and the necessary See also:foundation for such a theory was thus laid. We find the discussions about the true elements phlogiston disappearing from the See also:text-books, or removed to an theory. insignificant corner, while the description of observed chemical changes of different ways of preparing the same sub-stance, as identified by the same properties, and of the methods for recognizing and distinguishing the various substances, take their place. The similarity of certain groups of chemical changes, as, for example, See also:combustion, and the inverse process, reduction, was observed, and thus led to an See also:attempt to shape these most general facts into a common theory.

In this way the theory of " phlogiston " was developed by G.E. See also:

Stahl, phlogiston being (according to the usual way of regarding general properties as being due to a principle or element) the " principle of combustibility," similar to the " sulphur " of the alchemists. This again must be regarded as quite a legitimate step justified by the knowledge of the time. For experience taught that combustibility could be transferred by chemical See also:action, e.g. from See also:charcoal to litharge, the latter being changed thereby into combustible metallic lead; and according to Boyle's principle, that only bodies should be recognized as chemical elements, phlogiston was considered as a body. From the fact that all leading chemists in the second See also:half of the 18th century used the phlogiston theory and were not hindered by it in making their great discoveries, it is evident that a sufficient amount of truth and usefulness was embodied in this theory. It states indeed quite correctly the mutual relations between oxidation and reduction, as we now See also:call these very general processes, and was erroneous only in regard to one question, which at that time had not aroused much See also:interest, the question of the change of See also:weight during chemical processes. It was only after See also:Isaac See also:Newton's See also:discovery of universal See also:gravitation that weight was considered as a See also:property of See also:paramount interest and importance, and that the question of the changes of weight in chemical reactions became Bier Lav'soone See also:worth asking. When in due time this question was reform. raised, the fact became evident at once, that combustion means not loss but gain of weight. To be sure of this, it was necessary to know first the chemical and See also:physical properties of gases, and it was just at the same time that this knowledge was developed by See also:Priestley, See also:Scheele and others. See also:Lavoisier was the originator and expounder of the necessary reform. See also:Oxygen was just discovered at that time, and Lavoisier gathered See also:evidence from all sides that the theory of phlogiston had to be turned inside out to See also:fit the new facts. He realized that the sum See also:total of the weights of all sub-stances concerned within a chemical change is not altered by the change.

This principle of the " conservation of weight " led at once to a See also:

simple and unmistakable definition of a chemical element. As the weight of a compound substance is the sum of the weights of its elements, the compound necessarily weighs more than any of its elements. An element is therefore a sub-stance which, by being changed into another substance, in-variably increases its weight, and never gives rise to substances of less weight. By the help of this criterion Lavoisier composed the first table of chemical elements similar to our modern ones. According to the knowledge of his time he regarded the alkalis as elements, although he remarked that they are rather similar to certain oxides, and therefore may possibly contain oxygen; the truth of this was proved at a later date by See also:Humphry See also:Davy. But the inconsistency of the reformer, already referred to, may be observed with Lavoisier. He included " See also:heat and light " in his See also:list of elements, although he knew that neither of them had weight, and that neither fitted his definition of an element; this atavistic survival was subsequently removed from the table of the elements by See also:Berzelius in the beginning of the 19th century. In this way the question of what substances are to be regarded as chemical elements had been settled satisfactorily in a qualitative way, but it is interesting to realize that the last step in this development, the theory of Lavoisier, was based on quantitative considerations. Such considerations became of paramount interest at once, and led to the concept of the combining weights of the elements. The first discoveries in this See also:field were made in the last See also:quarter of the 18th century by J. B. See also:Richter.

The point at issue was a rather See also:

commonplace one: it was the fact that when two J. B. neutral salt solutions were mixed to undergo mutual work. ichter's chemical decomposition and recombination, the re- sulting liquid was neutral again, i.e. it did not contain any excess of See also:acid or base. In other words, if two salts, A'B' and A" B", composed of the acids A' and A" and the bases B' and B", undergo mutual decomposition, the amount of the base B' See also:left by the first salt, when its acid A' See also:united with the base B" to form a new salt A'B", was just enough to make a neutral salt A"B' with the acid A" left by the second salt. At first sight this looks quite simple and self-evident,—that neutral salts should form neutral ones again and not acid or basic ones, but if this fact is once stated very serious quantitative inferences may be See also:drawn from it, as Richter showed. For if the symbols A', A", B', B" denote at the same time such quantities of the acids and bases as form neutral salts, then if three of these quantities are determined, the See also:fourth may be calculated from the others. This follows from the fact that by decomposing A'B' with just the proper amount of the other salt to form A'B", the remaining quantities B' and A" exist in exactly the ratio to form a neutral salt A" B'. It is possible, therefore, to ascribe to each acid and base a certain relative weight or " combining weight " by which they will combine one with the other to form neutral salts. The same reasoning may be extended to any number of acids and bases. It is true that Richter did not find out by himself this simplest statement of the law of See also:neutrality which he discovered, but he expressed the same consequence in a rather clumsy way by a table of the combining weights of different bases related to the unit amount of a certain acid, and doing the same thing for the unit weight of every other acid. Then he observed that the See also:numbers in these different tables are proportionate one to another. The same holds See also:good if the corresponding See also:series of the combining weights of acids for unit weights of different bases were tabulated. It was only a little later that a See also:Berlin physicist, G.

E. See also:

Fischer, united the whole See also:system of Richter's numbers simply into a double table of acids and bases, taking as unit an arbitrarily chosen substance, namely sulphuric acid. The following table by Fischer is therefore the first table of combining weights. Bases. Acids. Alumina .. • 525 Fluoric . • 427 See also:Magnesia .. . 615 Carbonic . • 577 Ammoniac 672 Sebacic. 706 See also:Lime . . 793 Muriatic (hydrochloric) 712 Soda .

. • 859 Oxalic . . . 755 Strontiane 1329 Phosphoric . 979 Potash . . 1605 Formic . . 988 Baryte . . 2222 Sulphuric . See also:

I000 Succinic 1209 Nitric 1405 Acetic 1480 Citric .. . 1683 Tartaric 1694 It is interesting again to See also:notice how difficult it is for the discoverer of a new truth to find out the most simple and See also:complete statement of his discovery. It looks as if the amount of work needed to get to the See also:top of a new idea is so great that not enough See also:energy remains to clear the very last few steps. It is noteworthy also to observe how difficult it was for the chemists of that time to understand the bearing of Richter's work. Although a See also:summary of his results was published in Berthollet's Essai de statique chimique, one of the most renowned chemical books of that time, nobody dared for a See also:long time to take up the scientific treasure laid open for all the See also:world.

At the beginning of the 19th century the same question was taken up from quite another standpoint. See also:

John Dalton, in his investigations of the behaviour of gases, and in order to understand more easily what happened when gases were absorbed by liquids, used the corpuscular hypo- thesis already mentioned in connexion with Boyle. While he depicted to himself how the corpuscles, or, as he pre- ferred to call them, the "atoms" of the gases, entered the interstices of the atoms of the liquids in which they dissolved, he asked himself: Are the several atoms of the same substance exactly alike, or are there See also:differences as between the grains of See also:sand ? Now experience teaches us that it is impossible to See also:separate, for example, a quantity of pure water into two samples of somewhat different properties. When a pure substance is fractionated by partial See also:distillation or partial See also:crystallization or partial change into another substance by chemical means, we find constantly that the See also:residue is not changed in its properties, as it would be if the atoms were slightly different, since in that case e.g. the lighter atoms would distil first and leave behind the heavier ones, &c. Therefore we must conclude that all atoms of the same See also:kind are exactly alike in shape and weight. But, if this be so, then all combinations between different atoms must proceed in certain invariable ratios of the weights of the elements, namely by the ratio of the weights of the atoms. Now it is impossible to weigh the atoms directly; but if we determine the ratio of the weights in which oxygen and See also:hydrogen combine to form water, we determine in this way also the relative weight of their atoms. By a proper number of analyses of simple chemical compounds we may determine the ratios between the weights of all elementary atoms, and, selecting one of them as a See also:standard or unit, we may express the weight of all other atoms in terms of this unit. The following table is Dalton's (Mem. of the Lit. and Phil. See also:Soc. of See also:Manchester (II.), vol. i. p. 287, 1805).

Table of the Relative Weights of the Ultimate Particles of Gaseous and other Bodies. Hydrogen .. . I Nitrous See also:

oxide 13.7 Azot . 4.2 Sulphur . . . . 14.4 Carbone . 4.3 Nitric acid 15.2 See also:Ammonia . 5.2 Sulphuretted hydrogen 15.4 Oxygen . . 5.5 Carbonic acid 15.3 Water . . . . . . 6.5 See also:Alcohol .

. . 15.1 See also:

Phosphorus . . 7.2 Sulphureous acid . . . 19.9 Phosphuretted hydrogen . 8.2 Sulphuric acid . 25.4 9.3 Carburetted hydrogen from Nitrous See also:gas . . . . See also:Ether . . . . 9.6 stagnant water . . .

6.3 Gaseous oxide of carbone 9.8 Olefiant gas .. .. 5.3 Dalton at once See also:

drew a See also:peculiar inference from this view. If two elements combine in different ratios, one must conclude that different numbers of atoms unite. There must be, therefore, a simple ratio between the quantities of the one element united to the same quantity of the other. Dalton showed at once that the See also:analysis of See also:carbon monoxide and of carbonic acid satisfied this consequence, the quantity of oxygen in the second compound being double the quantity in the first one. A similar relation holds good between See also:marsh gas and olefiant gas (See also:ethylene). This is the " law of multiple proportions " (see Azom). By these considerations Dalton extended the law of combining weights, which Richter had demonstrated only for neutral salts, to all possible chemical compounds. While the See also:scope of the law was enormously extended, its experimental foundation was even smaller than with Richter. Dalton did not concern himself very much with the experimental verification of his ideas, and the first communication of his theory in a See also:paper on the absorption of gases by liquids (1803) attracted as little notice as Richter's discoveries. Even when T.

See also:

Thomson published Dalton's views in an appendix to his widely read text-See also:book of chemistry, matters did not change very much. It was only by the work of J. J. Berzelius that the enormous importance of Dalton's views was brought to light. Berzelius was at that time busy in developing a trustworthy system of chemical analysis, and for this purpose he investigated the See also:composition of the most important salts. He then went over the work of Richter, and realized that by his w°'* of law he could check the results of his analyses. He tried Be J. J. rzelius. it and found the law to hold good in most cases; when it did not, according to his analyses, he found that the See also:error was on his own See also:side and that better analyses fitted Richter's law. Thus he was prepared to understand the importance of Dalton's views and he proceeded at once to test its exactness. The result was the best possible.

The law of the combining weights of the John Dalton's atomic theory. atoms, or of the atomic weights, proved to hold good in every case in which it was tested. All chemical combinations between the several elements are therefore regulated by weight according to certain numbers, one for each element, and combinations between the elements occur only in ratios given by these weights or by simple multiples thereof. Consequently Berzelius regarded Dalton's atomic hypothesis as proved by experiment, and became a strong' believer in it. At the same time W. H. See also:

Wollaston had discovered independently the law of multiple proportions in the case of neutral and acid salts. He gave up further work when he learned of Dalton's ideas, but afterwards he pointed out that it was necessary to distinguish the hypothetical part in Dalton's views from their empirical part. The latter is the law of combining weights, or the law that chemical See also:combination occurs only according to certain numbers characteristic for each element. Besides this purely experimental law there is the hypothetical explanation by the See also:assumption of the existence of atoms. As it is not proved that this explanation is the only one possible, the existence of the law is not a See also:proof of the existence of the atoms. He there-fore preferred to call the characteristic combining numbers of the elements not " atomic weights " but " chemical equivalents." Although there were at all times chemists who shared Wollaston's cautious views, the atomic hypothesis found general See also:acceptance because of its ready adaptability to the most diverse chemical facts.

In our time it is even rather difficult to separate, as Wollaston did, the empirical part from the hypothetical one, and the concept of the See also:

atom penetrates the whole system of chemistry, especially organic chemistry. If we compare the work of Dalton with that of Richter we find a fundamental difference. Richter's inference as to the existence of combining weights in salts is based solely on an experimental observation, namely, the persistence of neutrality after double decomposition; Dalton's theory, on the contrary, is based on the hypothetical concept of the atom. Now, however favourably one may think of the See also:probability of the existence of atoms, this existence is really not an observed fact, and it is necessary therefore to ask: Does there exist some general fact which may lead directly to the inference of the existence of combining weights of the elements, just as the persistence of neutrality leads to the same consequence as to acids and bases ? The See also:answer is in the affirmative, although it took a whole century before this question was put and answered. In a series of rather difficult papers (gel's. f. Phys. Chem. since 1895, and Annalen der Naturphilosophie since 1902), See also:Franz Wald (of See also:Kladno, Bohemia) developed his investigations as to the See also:genesis of this general law. Later, W. Ostwald (See also:Faraday lecture, Trans. Chem. Soc., 1904) simplified Wald's reasoning and made it more evident.

The general fact upon which the necessary existence of combining weights of the elements may be based is the shifting character of the boundary between elements and compounds. It has already been pointed out that Lavoisier considered the alkalis and the alkaline earths as elements, because in his time they had not been decomposed. As long as the decomposition had not been effected, these compounds could be considered and treated like elements without See also:

mistake, their combining weight being the sum of the combining weights of their (subsequently discovered) elements. This means that compounds enter in reaction with other substances as a whole, just as elements do. In particular, if a compound AB combines with another substance (elementary or compound) C to form a ternary compound ABC, it enters this latter as a whole, leaving behind no residue of A or B. Inversely, if a ternary compound ABC be changed into a binary one AB by taking away the element C, there will not be found any excess of A or B, but both elements will exhibit just the same ratio in the binary as in the ternary compound. Experimentally this important fact was proved first by Berzelius, who showed that by oxidizing lead sulphide, See also:PbS, to lead sulphate, PbSO4i no excess either of sulphur or lead could be found after oxidation; the same held good with See also:barium sulphite, BaSO3, when converted into barium sulphate, BaSO4. On a much larger See also:scale and with very great accuracy the inverse was proved half a century later by J. S. See also:Stas, who reduced See also:silver chlorate, AgC1O3, silver bromate, AgBrO3, and silver iodate, AgIO3, to the corresponding binary compounds, AgCI, AgBr and AgI, and searched in the residue of the reaction for any excess of silver or halogen. As the tests for these substances are among the most sensitive in analytical chemistry, the general law underwent a very severe test indeed. But the result was the same as was found by Berzelius--no excess of one of the elements could be discovered.

We may infer, therefore, generally that compounds enter ulterior combinations without change of the ratio of their elements, or that the ratio between different elements in their compounds is the same in binary and ternary (or still more complicated) combinations. This law involves the existence of general combining weights just in the same way as the law of neutrality with double de-composition of salts involves the law of the combining weights of acids and bases. For if the ratio between A and B is deter-See also:

mined, this same ratio must obtain in all ternary and more complicated compounds, containing the same elements. The same is true for any other elements, C, D, E, F, &c., as related to A. But by applying the general law to the ternary compound ABC the same conclusion may be drawn as to the ratio A: C in all compounds containing A and C, or B : C in the corresponding compounds. By reasoning further in the same way, we come to the conclusion that only such compounds are possible which contain elements according to certain ratio-numbers, i.e. their combining weight. Any other ratio would violate the law of the integral reaction of compounds. As to the law of multiple proportions, it may be deduced by a similar reasoning by considering the possible combinations between a compound, e.g. AB, and one of its elements, say B. AB and B can combine only according to their combining weights, and therefore the quantity of B combining with AB is equal to the quantity of AB which has combined with A to form AB. The new combination is therefore to be expressed by AB2. By extending this reasoning in the same way, we get the general conclusion that any compounds must be composed according to the See also:formula A„ BnCp ..., where m, n, p, &c., are integers.

The bearing of these considerations on the atomic hypothesis is not to disprove it, but rather to show that the existence of the law of combining weights, which has been considered for so long as a proof of the truth of this hypothesis, does not necessarily involve such a consequence. Whether atoms may prove to exist or not, the law of combining weights is See also:

independent thereof. Two problems arose from the discoveries of Dalton and Berzelius. The first was to determine as exactly as possible the correct numbers of the combining weights. The other Atomic results from the fact that the same elements may weight combine in different ratios. Which of these ratios determinagives the true ratio of the atomic weights? And tions. which is the multiple one? Both questions have had most ample experimental investigation, and are now answered rather satisfactorily. The first question was a purely technical one; its answer depended upon analytical skill, and Berzelius in his time easily took the lead, his numbers being readily accepted on the See also:continent of See also:Europe. In See also:England there was a certain hesitation at first, owing to See also:Prout's assumption (see below), but when See also:Turner, at the instigation of the See also:British Association for the See also:Advancement of Science, tested Berzelius's numbers and found them entirely in accordance with his own measurements, these numbers were universally accepted. But then a rather large error in one of Berzelius's numbers (for carbon) was discovered in 1841 by See also:Dumas and Stas, and a kind of panic ensued. New determinations of the atomic weights were undertaken from all sides.

The result was most satisfactory for Berzelius, for no other important error was discovered, and even Dumas remarked that repeating a determination by Berzelius only meant getting the same result, if one worked properly. In later times more exact measurements, corresponding to the increasing art in analysis, were carried out by various workers, amongst whom J. S. Stas distinguished himself. But even the classical work of Stas proved not to be entirely without error; for every See also:

period has its limit in accuracy, which extends slowly as science extends. In See also:recent times See also:American chemists have been especially prominent in work of this kind, and the determinations of E. W. See also:Morley, T. W. See also:Richards and G. P. See also:Baxter See also:rank among the first in this See also:line of investigation.

During this work the question arose naturally: How far does the exactness of the law extend? It is well known that most natural See also:

laws are only approximations, owing to disturbing causes. Are there disturbing causes also with atomic weights ? The answer is that as far as we know there are none. The law is still an exact one. But we must keep in mind that an See also:absolute answer is never possible. Our exactness is in every case limited, and as long as the possible See also:variations See also:lie behind this limit, we cannot tell anything about them. In recent times H. Landolt has doubted and experimentally investigated the law of the conservation of weight. Landolt's experiments were carried out in vessels of the shape of an inverted U, each See also:branch holding one of the substances to react one on the other. Two vessels were prepared as equal as possible and hung on both sides of a most sensitive See also:balance. Then the difference of weight was determined in the usual way by exchanging both the vessels on the balance.

After this set of weighings one of the vessels was inverted and the chemical reaction between the contained substances was performed; then the double weighing was repeated. Finally also the second See also:

vessel was inverted and a third set of weighings taken. From See also:blank experiments where the vessels were filled with substances which did not react one on the other, the maximum error was determined to o•c3 milligramme. The reactions experimented with were: silver salts with ferrous sulphate; iron on copper sulphate; gold chloride and ferrous chloride; iodic acid and hydriodic acid; See also:iodine and See also:sodium sulphite; uranyl nitrate and See also:potassium See also:hydrate; See also:chloral hydrate and potassium hydrate; See also:electrolysis of See also:cadmium iodide by an alternating current; See also:solution of ammonium chloride, potassium bromide and uranyl nitrate in water, and precipitation of an aqueous solution of copper sulphate by alcohol. In most of these experiments a slight diminution of weight was observed which exceeded the limit of error distinctly in two cases, viz, silver nitrate with ferrous sulphate and iodic acid with hydriodic acid, the loss of weight amounting from o•o68 to 0.199 mg. with the first and 0.047 to 0.177 mg. with the second reaction on about 5o g. of substance. As each of these reactions had been tried in nine independent experiments, Landolt felt certain that there was no error of observation involved. 'See also:nut when the vessels were covered inside with See also:paraffin See also:wax, no appreciable diminution of weight was observed. These experiments apparently suggested a small decrease of weight as a consequence of chemical processes. On repeating them, however, and making See also:allowance for the different amounts of water absorbed on the See also:surface of the vessel at the beginning and end of the experiment, Landolt found in 1908 (Zeit. physik. Chem. 64, p. 581) that the variations in weight are equally See also:positive and negative, and he concluded that there was no change in weight, at least to the extent of 1 part in io,000,000.

There is still another question regarding the numerical values of the atomic weights, namely: Are there relations between the numbers belonging to the several elements? Richter had arranged his combining weights according to their magnitude, and en- deavoured to prove that they form a certain mathematical series. He also explained the incompleteness of his series by assuming that certain acids or bases requisite to the filling up of the gaps in the series, were not yet known. He even had the See also:

satisfaction that in his time a new base was discovered, which fitted rather well into one of his gaps; but when it turned out afterwards that this new base was only See also:calcium phosphate, this way of reasoning See also:fell into discredit and was resumed only at a much later date. To obtain a correct table of atomic weights the second question already mentioned, viz. how to select the correct value in the case of multiple proportions, had to be answered. Berzelius was constantly on the look-out for means to distinguish the true atomic weights from their multiples or sub-multiples, but he could not find an unmistakable test. The whole question fell into a terrible disorder, until in the middle of the 19th century S. See also:Cannizzaro showed that by taking together all partial evidences one could get a system of atomic weights consistent in itself and fitting the exigencies of chemical systematics. Then a startling discovery was made by the same method which Richter had tried in vain, by arranging all atomic weights in one series according to their numerical values. The Periodic Law.-The See also:history of this discovery is rather long. As See also:early as 1817 J. W.

See also:

Dobereiner of See also:Jena drew See also:attention to the fact that the combining weight of See also:strontium lies midway between those of calcium and barium, and some years later he showed that such " triads " occurred in other cases too. L. See also:Gmelin tried to apply this idea to all elements, but he realized that in many cases more than three elements had to be grouped together. While See also:Ernst Lenssen applied the idea of triads to the whole table of chemical elements, but without any important result, the other idea of grouping more than three elements into series according to their combining weights proved more successful. It was the concept of homologous series just developed in organic chemistry which influenced such considerations. First Max von See also:Pettenkofer in 185o and then J. B. A. Dumas in 1851 undertook to show that such a series of similar. elements could be formed, having nearly See also:constant differences between their combining weights. It is true that this idea in all its simplicity did not hold good extensively enough; so J. P. See also:Cooke and Dumas tried more complicated types of numerical series, but only with a temporary success.

The idea of arranging all elements in a single series in the order of the magnitude of their combining weights, the germ of which is to be found already in J. B. Richter's work, appears first in 186o in some tables published by Lothar See also:

Meyer for his lectures. Independently, A. E. B. de Chancourtois in 1862, J. A. R. See also:Newlands in 1863, and D. I. Mendeleeff in 1869, developed the same idea with the same result, namely, that it is possible to See also:divide this series of all the elements into a certain number of very similar parts. In their papers, which appeared in the same See also:year, 1869, Lothar•Meyer and Mendeleeff gave to all these trials the shape now generally adopted.

They succeeded in proving beyond all doubt that this series was of a periodic character, and could be cut into shorter pieces of similar construction. Here again gaps were present to be filled up by elements to be discovered, and Mendeleeff , who did this, predicted from the general regularity of his table the properties of such unknown elements. In this case See also:

fate was more kind than with Richter, and science had the satisfaction of seeing these predictions turn out to be true. The following table contains this periodic arrangement of the elements according to their atomic weight. By cutting the whole series into pieces of eight elements (or more in several The periodic arangement. He 4.0 Li 7.03 Be 9.1 B 11.0 C 12.00 N 14.01 0 16.00 F 19.0 Ne 20 Na 23.00 Mg 24.32 Al 27.1 Si 28.4 P 31.0 S 32.06 Cl 35.45 Ar 39.9 K 39.15 Ca 40.1 Sc 44.1 Ti 48.1 V 51.2 Cr 52.0 Mn 55.0 Fe 55.9, Ni 58.7, Co 59.0 Cu 63.6 In 65.4 Ga 70 Cie 72.5 As 75.0 Se 79.2 Br 79.96 .. . . Kr 83.0 Rb 85.5 Sr 87.6 Y 89•o Zr 90.6 Cb(Nb) 94 Mo 96.0 Ru 101.7, Rh 103.0, Pd x06.5 Ag 107.93 Cd 112.4 In 115 Sn 119.0 Sb 120.2 Te 127.6 I 126.97 . Xe 130.7 Cs 132.9 Ba 137.4 La 1389 Ce &c. 14o Ta 181 W 184 Os 191, Ir 193.0, Pt 194.8 Au 197.2 Hg 200.0 Ti 204.1 Pb 206.9 Bi 208.0 .. .. ..

. . Ra 225 Th 232.5 .. U 2385 it cases) and arranging these one below another in the alternating way shown in the table, one finds similar elements placed in See also:

vertical series whose properties change gradually and with some regularity according to their place in the table. Not only the properties of the uncombined elements obey this See also:rule, but also almost all properties of similar compounds of the elements. But upon closer investigation it must be confessed that these regularities can be called only rules, and not laws. In the first line one would expect that the steps in the values of the atomic weights should be See also:regular, but it is not so. There are even cases when it is necessary to invert the order of the atomic weights to satisfy the chemical necessities. Thus See also:argon has a larger number than potassium, but must precede it to fit into its proper place. The same is true of See also:tellurium and iodine. It looks as if the real elements were scattered somewhat haphazard on a regular table, or as if some independent See also:factor were active to disturb an existing regularity. It may be that the new facts mentioned above will lead also to an explanation of these irregularities; at present we must recognize them and not try to explain them away. Such considerations have to be kept in mind especially in regard to the very numerous attempts• to express the series of combining weights in a mathematical form.

In several cases rather surprising agreements were found, but never without exception. It looks as if some very important factor regulating the whole See also:

matter is still unknown, and before this has been elucidated no satisfactory treatment of the matter is possible. It seems therefore premature to enter into the details of these speculations. In recent times not only our belief in the absolute exactness of the law of the conservation of weight has been shaken, but also our belief in the law of the conservation of the fraosmo- mama of elements. The wonderful substance See also:radium, whose tation of dements. existence has made us to revise quite a number of old and established views, seems to be a fulfilment of the .ild problem of the alchemists. It is true that by its help lead 13 not changed into gold, but radium not only changes itself into another element, See also:helium (See also:Ramsay), but seems also to cause other elements to change. Work in this line is of present day origin only and we do not know what new laws will be found to regulate these most unexpected reactions (see See also:RADIOACTIVITY). But we realize once more that no law can be regarded as See also:free from See also:criticism and See also:limitation; in the whole See also:realm of exact sciences there is no such thing as the Absolute. Another question regarding the values of atomic weights was raised very soon after their first See also:establishment. From the some- what inexact first determinations See also:William Prout Prout's concluded that all atomic weights are multiples of the assrrmp. See also:Lion. atomic weight of hydrogen, thus suggesting all other elements to be probably made up from condensed hydrogen. Berzelius found his determinations not at all in accordance with this assumption, and strdngly opposed the arbitrary Iounding off of the numbers practised by the partisans of Prout's hypothesis.

His hypothesis remained alive, although almost every chemist who did exact atomic weight determinations, especially Stas, contradicted it severely. Even in our time it seems to have followers, who See also:

hope that in some way the existing experimental differences may disappear. But one of the most important and best-known relations, that between hydrogen and oxygen, is certainly different from the simple ratio I :16, for it has been determined by a large number of different investigators and by different methods to be undoubtedly See also:lower, namely, I :15.87. Therefore, if Prout's hypothesis contain an element of truth, by the See also:act of condensation of some simpler substance into the present chemical elements a change of weight also must have occurred, such that the weight of the element did not remain exactly the weight of the simpler substance which changed into it. We have already remarked that such phenomena are not yet known with certainty, but they cannot be regarded as utterly impossible. It may here be mentioned that the internationality of science has shown itself active also in the question of atomic weights. These numbers undergo incessantly small variations becauseof new work done for their determination. To avoid the uncertainty arising from this inevitable See also:state of affairs, an See also:international See also:committee was formed by the co-operation of the leading chemical See also:societies all over the world, and an international table of the most probable values is issued every year. The following table is that for 1910: International Atomic Weights, 19TO. Atomic Atomic Weights. Weights. Name.

See also:

Symbol. 0 =16. Name. Symbol. 0 =16. See also:Aluminium Al 27•I Mercury . . Hg 200.0 See also:Antimony Sb I20•2 See also:Molybdenum Mo 96•o Argon. Ar 39'9 Neodymium . Nd 144'3 See also:Arsenic . . . As 74.96 Neon . . Ne 20.0 Barium .

. . Ba 137'37 See also:

Nickel Ni 58.68 See also:Beryllium . Be See also:Nitrogen N 14.0I . (See also:Glucinum) . Cl c 9.1 See also:Osmium . Os 190.9 See also:Bismuth . Bi 208.0 Oxygen . 0 16•oo See also:Boron. . . B 11 .o See also:Palladium Pd Io6.7 See also:Bromine Br 7992 Phosphorus P 31.0 Cadmium Cd 112.40 See also:Platinum. Pt 195.0 See also:Caesium . . Cs 132.81 Potassium .

K 39.10 Calcium Ca 40.09 Praseodymium Pr 140.6 Carbon C 12.00 Radium . . Ra 226.4 See also:

Cerium . . . Ce 140.25 See also:Rhodium. Rh 102.9 See also:Chlorine . . Cl 35.46 See also:Rubidium . Rb 85.45 See also:Chromium . . Cr 52.0 See also:Ruthenium . Ru I01.7 See also:Cobalt . . . Co 58.97 Samarium Sm 150.4 See also:Columbium . . Cb See also:Scandium Sc 44.1 (Niobium).

. (Nb) 93'5 See also:

Selenium Se 79.2 Copper . . . Cu 63'57 See also:Silicon Si 28.3 Dysprosium . . Dy 162.5 Silver Ag 107.88 See also:Erbium . . . Er 167.4 Sodium . Na 23.00 See also:Europium . . Eu 152.0 Strontium Sr 87.62 See also:Fluorine . . . F 19.0 Sulphur . S 32'07 See also:Gadolinium . . Gd 157'3 See also:Tantalum Ta 181•o See also:Gallium .

. . Ga 69.9 Tellurium Te 127.5 See also:

Germanium . . Ge 72.5 See also:Terbium . Tb 159'2 Gold . . Au 197.2 See also:Thallium Tl 204.0 Helium He 4.0 See also:Thorium . Th 232'42 Hydrogen H I•oo8 Thulium Tm 168.5 See also:Indium . In 114.8 See also:Tin Sn 119.0 Iodine I 126.92 See also:Titanium. Ti 48.1 See also:Iridium . Ir 193.1 See also:Tungsten. W 184•o Iron . . Fe 55.85 See also:Uranium . . U 238.5 Krypton .

Kr 83.0 See also:

Vanadium . V 51.2 Lanthanum . La 139.0 Xenon Xe 130.7 Lead . . Pb 207.10 See also:Ytterbium (Neo- See also:Lithium . . Li 7.00 ytterbium) . Yb 172.0 Lutecium. . Lu 174 0 See also:Yttrium . . . Y 89.o See also:Magnesium . . Mg 24.32 See also:Zinc . . . . Zn 65.37 See also:Manganese .

. Mn 54.93 See also:

Zirconium . . Zr 9o•6 In the long and manifold development of the concept of the element one idea has remained prominent from the very beginning down to our times: it is the idea of a primordial matter. Since the naive statement of Thales that all cOn° clnding things came from water, chemists could never reconcile remarts. themselves to the fact of the conservation of the elements. By an experimental investigation which extended over five centuries and more, the impossibility of transmuting one element into another-for example, lead into gold-was demonstrated in the most extended way, and nevertheless this law has so little entered the consciousness of the chemists that it is seldom explicitly stated even in carefully written text-books. On the, other side the attempts to reduce the manifoldness of the actual chemical elements to one single primordial matter have never ceased, and the latest development of science seems to endorse such a view. It is therefore necessary to consider this question from a most general standpoint. In physical science, the chemical elements may be compared with such concepts as See also:mass, momentum, quantity of electricity, entropy and such like. While mass and entropy are determined univocally by a unit and a number, quantity of electricity has a unit, a number and a sign, for it can be positive as well as negative. Momentum has a unit, a number and a direction in space. Elements do not have a common unit as the former magnitudes, but every element has its own unit, and there is no transition from one to another. All these magnitudes underlie a law of conservation, but to a very different degree. While mass was Inter-See also:national table of atomic weights.

considered as absolutely invariable in the classical See also:

mechanics, the newer theories of the See also:electrical constitution of matter make mass dependent on the velocity of the moving See also:electron. Momentum also is not entirely conservative because it can be changed by light-pressure. Entropy is known as constantly increasing, remaining constant only in an ideal limiting case. With chemical elements we observe the same thing as with momentum; though till recently considered as conservative, there is now experimental evidence that they do not always show this character. Generally the laws of the conservation of mass, weight and elements are expressed as the " law of the conservation of matter." But this expression lacks scientific exactness because the term " matter " is generally not defined exactly, and because only the above-named properties of ponderable See also:objects do not change, while all other properties do to a greater or less extent. Considered in the most general way, we may define matter as a complex of gravitational, kinetic and chemical energies, which are found to cling together in the same space. Of these energies the capacity factors, namely, weight, mass and elements, are conservative as described, while the intensity factors, potential, velocity and See also:affinity, may change in wide limits. To explain why we find these energies constantly combined one with another, we only have to think of a mass without gravity or a ponderable body without mass. The first could not remain on earth because every See also:movement would carry it into See also:infinite space, and the second would acquire infinite velocity by the slightest push and would also disappear at once. Therefore only such objects which have both mass and weight can be handled and can be objects of our knowledge. In the same way all other energies come to our knowledge only by being (at least temporarily) associated with this combination of mass and weight. This is the true meaning of the term " matter." In this line of ideas matter appears not at all as a See also:primary concept, but as a complex one; there is therefore no reason to consider matter as the last term of scientific analysis of chemical facts, and the idea of a primordial matter appears as a survival from the very first beginning of See also:European natural philosophy.

The most general concept science has developed to express the variety of experience is energy, and in terms of energy (combined with number, magnitudes, time and space) all observed and observable experiences are to be described. (W.

End of Article: ELEMENT (Lat. elementum)

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