CHAPTER VI

THE AGE OF MODERN CHEMISTRY
§ 71. Chemistry as distinct from Alchemy and
latro-chemistry commenced with Robert Boyle (see
plate 15), who first clearly recognised
The Birth of ^\^g^^ j^-g ^jj^ jg neither the transmutation of
Modem , , , . - ,.
Chemistry. ^^^ metals nor the preparation 01 medi- cines, but the observation and generalisa- tion of a certain class of phenomena ; who denied the validity of the alchemistic view of the constitution of matter, and enunciated the definition of an element which has since reigned supreme in Chemistry ; and who enriched the science with observations of the utmost importance. Boyle, however, was a man whose ideas were in advance of his times, and inter- vening between the iatro-chemical period and the Age of Modern Chemistry proper came the period of the Phlogistic Theory — a theory which had a certain affinity with the ideas of the alchemists.
§ 72. The phlogiston theory was mainly due to Georg Ernst Stahl (i 660-1 734). Becher (1635- 1682) had attempted to revive the once universally accepted sulphur- mercury-salt theory of the alchem- ists in a somewhat modified form, by the assump- tion that all substances consist of three earths — the
PLATK 15.
•^y ^f.A'ij^ArnZeruH'nl .
PORTRAIT OF ROBEKT BOYLE.
pa^c 94]
§ 72] AGE OF MODERN CHEMISTRY 95
combustible, mercurial, and vitreous ; and herein is to be found the germ of Stahl's phlogistic theory. According to Stahl, all combustible bodies T^® (including those metals that change on
Theory!^ heating) contain phlogiston, the principle of combustion, which escapes in the form of flame when such substances are burned. According to this theory, therefore, the metals are compounds, since they consist of a metallic calx (what we now call the ** oxide" of the metal) combined with phlogiston; and, further, to obtain the metal from the calx it is only necessary to act upon it with some substance rich in phlogiston. Now, coal and charcoal are both almost completely combustible, leaving very little residue ; hence, according to this theory, they must consist very largely of phlogiston ; and, as a matter of fact, metals can be obtained by heating their calces with either of these substances. Many other facts of a like nature were explicable in terms of the phlogiston theory, and it became exceedingly popular. Chemists at this time did not pay much attention to the balance ; it was observed, however, that metals increased in weight on calcination, but this was *' explained " on the assumption that phlogiston possessed negative weight. Antoine Lavoisier (i 743-1 794), utilising Priestley's discovery of oxygen (called ** dephlogisticated air " by its discoverer) and studying the weight relations accompanying combustion, demonstrated the non- validity of the phlogistic theory^ and proved com- bustion to be the combination of the substance burnt
* It should be noted, however, that if by the term " phlogiston " we were to understand energy and not some form of matter, most of the statements of the phlogistics would be true so far as they go.
96 ALCHEMY [§ 73
with a certain constituent of the air, the oxygen. By this time Alchemy was to all intents and purposes defunct, Boerhave (i 668-1 738) was the last eminent chemist to give any support to its doctrines, and the new chemistry of Lavoisier gave it a final death-blow. We now enter upon the Age of Modern Chemistry, but we shall deal in this chapter with the history of chemical theory only so far as is necessary in pursuance of our primary object, and hence our account will be very far from complete.
§ 73. Robert Boyle (i 626-1 691) had defined an element as a substance which could not be decom- posed, but which could enter into combi-
Boyle and the nation with other elements 2:ivinpf com-
Definition , , , ^ , ^ . . .
of an Element, po^^^ds capable 01 decomposition into
these original elements. Hence, the
metals were classed among the elements, since they
had defied all attempts to decompose them. Now, it
must be noted that this definition is of a negative
character, and, although it is convenient to term
** elements" all substances which have so far defied
decomposition, it is a matter of impossibility to decide
what substances are true elements with absolute
certainty ; and the possibility, however faint, that
gold and other metals are of a compound nature, and
hence the possibility of preparing gold from the
*' base " metals or other substances, must always
remain. This uncertainty regarding the elements
appears to have generally been recognised by the
new school of chemists, but this having been so, it is
the more surprising that their criticism of alchemistic
art was not less severe.
74. With the study of the relative weights in
§ 75] AGE OF MODERN CHEMISTRY 97
which substances combine, certain generalisations or ** natural laws" of supreme importance were dis- covered. These stoichiometric laws, as
^^® . they are called, are as follows : — Stoicmometnc .. 1-1 t r r^ -n
La^s^ I. ** ihe Law of Constant Propor-
tion " — ne same chemical compound always contains the same elements, and there is a constant ratio between the weights of the constituent elements present.
2. *'The Law of Multiple Proportions" — If two substances combine chemically in more than one pro- portion^ the weights of the one which combine with a given weight of the other, stand in a simple rational ratio to one another.
3. " The Law of Combining Weights" — Substances combine either in the ratio of their combining numbers, or in simple rational multiples or submultiples of these numbers. (The weights of different substances which combine with a given weight of some particular substance, which is taken as the unit, are called the combining numbers of such substances with reference to this unit. The usual unit now chosen is 8 grammes of Oxygen.)^
As examples of these laws we may take the few
following simple facts : —
* In order that these laws may hold good, it is, of course, neces- sary that the substances are weighed under precisely similar con- ditions. To state these laws in a more absolute form, we can replace the term "weight" by "mass," or in preference, "inertia**; for the inertias of bodies are proportional to their weights, providing that they are weighed under precisely similar conditions. For a discussion of the exact significance of these terms "mass" and "inertia," the reader is referred to the present writer's Matter, Spirit and the Cosmos (Rider, 1910), Chapter I., "On the Doctrine of the Indestructibility of Matter."
98 ALCHEMY [§ U
1. Pure water is found always to consist of oxygen and hydrogen combined in the ratio of i 'ooS parts by weight of the latter to 8 parts by weight of the former ; and pure sulphur-dioxide, to take another example, is found always to consist of sulphur and oxygen combined in the ratio of 8*02 parts by weight of sulphur to 8 parts by weight of oxygen. (The Law of Constant Proportion.)
2. Another compound is known consisting only of oxygen and hydrogen, which, however, differs entirely in its properties from water. It is found always to consist of oxygen and hydrogen combined in the ratio of I '008 parts by weight of the latter to 16 parts by weight of the former, z.e,, in it a definite weight of hydrogen is combined with an amount of oxygen exactly twice that which is combined with the same weight of hydrogen in water. No definite compound has been discovered with a constitution intermediate between these two. Other compounds consisting only of sulphur and oxygen are also known. One of these (viz., sulphur-trioxide, or sulphuric anhydride) is found always to consist of sulphur and oxygen combined in the ratio of 5*35 parts by weight of sulphur to 8 parts by weight of oxygen. We see, therefore, that the weights of sulphur combined with a definite weight of oxygen in the two compounds called respectively *' sulphur-dioxide " and " sulphur-tri- oxide," are in the proportion of 8*02 to 5*35, i.e., 3 : 2. Similar simple ratios are obtained in the case of all the other compounds. (The Law of Multiple Proportions.)
3. From the data given in (i) above we can fix the combining number of hydrogen as i'oo8, that of
§ 75] AGE OF MODERN CHEMISTRY 99
sulphur as 8*02. Now, compounds are known con- taining sulphur and hydrogen, and, in each case, the weight of sulphur combined with i*oo8 grammes of hydrogen is found always to be either 8*02 grammes or some multiple or submultiple of this quantity. Thus, in the simplest compound of this sort, con- taining only hydrogen and sulphur (viz., sulphuretted- hydrogen or hydrogen sulphide), i*oo8 grammes of hydrogen is found always to be combined with 16-04 grammes of sulphur, i.e., exactly twice the above quantity. (The Law of Combining Weights.)
Berthollet (1748-1822) denied the truth of the law of constant proportion, and hence, of course, the other stoichiometric laws, and a controversy ensued between this chemist and Proust (i 755-1 826), who undertook a research to settle the question and in whose favour the controversy was ultimately decided.
§ 75. At the beginning of the nineteenth century,
John Dalton (see plate 15) put forward his Atomic
Theory in explanation of these facts.
Dalton's This theory assumes (i) that all matter
Theory. ^^ made up of small indivisible and in- destructible particles, called "atoms"; (2) that all atoms are not alike, there being as many different sorts of atoms as there are elements; (3) that the atoms constituting any one element are exactly alike and are of definite weight ; and (4) that com- pounds are produced by the combination of different atoms. Now, it is at once evident that if matter be so constituted, the stoichiometric laws must necessarily follow. For the smallest particle of any definite com- pound (now called a "molecule") must consist of a definite assemblage of different atoms, and these
100 ALCHEMY [§ 75
atoms are of definite weight : whence the law of constant proportion. One atom of one substance may combine with i, 2, 3 . . . atoms of some other sub- stance, but it cannot combine with some fractional part of an atom, since the atoms are indivisible : whence the law of multiple proportions. And these laws holding good, and the atoms being of definite weight, the law of combining weights necessarily follows. Dalton's Atomic Theory gave a simple and intelligible explanation of these remarkable facts regarding the weights of substances entering into chemical combina- tion, and, therefore, gained universal acceptance. But throughout the history of Chemistry can be discerned a spirit of revolt against it as an explanation of the absolute constitution of matter. The tendency of scientific philosophy has always been towards Monism as opposed to Dualism, and here were not merely two eternals, but several dozen ; Dalton's theory denied the unity of the Cosmos, it lacked the unifying principle of the alchemists. It is only in recent times that it has been recognised that a scientific hypothesis may be very useful without being altogether true. As to the usefulness of Dalton's theory there can be na question ; it has accomplished that which no other hypothesis could have done ; it rendered the concepts of a chemical element, a chemical compound and a chemical reaction definite ; and has, in a sense, led to the majority of the discoveries in the domain of Chemistry that have been made since its enunciq,tion. But as an expression of absolute truth, Dalton's theory, as is very generally recognised nowadays, fails to be satisfactory. In the past, however, it has been the philosophers of the materialistic school of thought,
PLATE i6.
Can'kfSc
PORTRAIT OF JOHN DALTON.
To face page icoj
§ 75] AGE OF MODERN CHEMISTRY 101
rather than the chemists qua chemists, who have insisted on the absolute truth of the Atomic Theory ; Kekul^, who by developing Franklin's theory of atomicity or valency 3 made still more definite the atomic view of matter, himself expressed grave doubts as to the absolute truth of Dalton's theory ; but he regarded it as chemically true, and thus voices what appears to be the opinion of the majority of chemists nowadays, namely, there are such things as chemical atoms and chemical elements, incapable of being decomposed by purely chemical means, but that such are not absolute atoms or absolute elements, and
3 The term " valency " is not altogether an easy one to define ; we will, however, here do our best to make plain its significance. In a definite chemical compound we must assume that the atoms constituting each molecule are in some way bound together (though not, of course, rigidly), and we may speak of " bonds " or " links of affinity," taking care, however, not to interpret such terms too literally. Now, the number of " affinity links " which one atom can exert is not unlimited \ indeed, according to the valency theory as first formulated, it is fixed and constant. It is this number which is called the " valency " of the element ; but it is now known that the " valency " in most cases can vary between certain limits. Hydro- gen, however, appears to be invariably univalent, and is therefore taken as the unit of valency. Thus, Carbon is quadrivalent in the methane- molecule, which consists of one atom of carbon combined with four atoms of hydrogen ; and Oxygen is divalent in the water- molecule, which consists of one atom of oxygen combined with two atoms of hydrogen. Hence, we should expect to find one atom of carbon combining with two of oxygen, which is the case in the carbon-dioxide — (carbonic anhydride) — molecule. The under- lying reason of this regularity remains unknown (see § 8i), and there are very many curious exceptions to it. For a development of the thesis, so far as the compounds of carbon are concerned, that each specific " affinity link " corresponds in general to a definite and constant amount of energy, which is evolved as heat on disruption of the bond, the reader is referred to the present writer's monograph On the Calculation of Thermo- Chemical Constants (Arnold, 1909).
102 ALCHEMY [§ 77
consequently not impervious to all forms of action.
But of this more will be said later.
§ 76. With the acceptance of Dalton's Atomic
Theory, it became necessary to determine the atomic
weights of the various elements, i.e., not
Determination ^^^ absolute atomic weights, but the
of the Atomic relative weights of the various atoms
Weights of ^j|.]-^ reference to one of them as unit.4 the Elements. ___ . . . ,
We cannot m this place enter upon a
discussion of the various difficulties, both of an experi- mental and theoretical nature, which were involved in this problem, save to remark that the correct atomic weights could be arrived at only with the acceptance of Avogadro's Hypothesis. This hypothesis, which is to the effect that equal volumes of different gases measured at the same temperature and pressure contain an equal number of gaseous molecules, was put forward in explanation of a number of facts connected with the physical behaviour of gases ; but its importance was for some time unrecognised, owing to the fact that the distinction between atoms and molecules was not yet clearly drawn. A list of those chemical substances at present recognised as " ele- ments," together with their atomic weights, will be found on pp. io6, 107.
§ 77. It was observed by a chemist of the name of Prout, that, the atomic weight of hydrogen being taken
♦ Since hydrogen is the lightest of all known substances, the unit, Hydrogen = i, was atone time usually employed. However, it was seen to be more convenient to express the atomic weights in terms of the weight of the oxygen-atom, and the unit. Oxygen = i6 is now always employed. This value for the oxygen-atom was chosen so that the approximate atomic weights would in most cases remain unaltered by the change.
§ 77] AGE OF MODERN CHEMISTRY 103
as the unit, the atomic weights of nearly all the ele- ments approximated to whole numbers ; and in 1 8 1 5
he suggested as the reason for this regu- ^°?* ^. larity, that all the elements consist solely
of hydrogen. Prout's Hypothesis received on the whole a very favourable reception ; it harmonised Dalton's Theory with the grand concept of the unity of matter — all matter was hydrogen in essence ; and Thomas Thomson undertook a research to demon- strate its truth. On the other hand, however, the eminent Swedish chemist, Berzelius, who had carried out many atomic weight determinations, criticised both Prout's Hypothesis and Thomson's research (which latter, it iis true, was worthless) in most severe terms ; for the hypothesis amounted to this — that the decimals in the atomic weights obtained experimentally by Berzelius, after so much labour, were to be regarded as so many errors. In 1844, Marignac suggested half the hydrogen atom as the unit, for the element chlorine, with an atomic weight ^^ 35*5» would not fit in with Prout's Hypothesis as originally formulated ; and later, Dumas suggested one-quarter. With this theoretical division of the hydrogen-atom, the hypothesis lost its simplicity and charm, and was doomed to downfall. Recent and most accurate atomic weight determinations show clearly that the atomic weights are not exactly whole numbers, but that, nevertheless, the majority of them (if expressed in terms of 0= 16 as the unit) do approxi- mate very closely to such. The Hon. R. J. Strutthas recently calculated that the probability of this occur- ring, in the case of certain of the commoner elements, by mere chance is exceedingly small (about i in
104 ALCHEMY [§ 77
i,ooo.)5 Several hypotheses attempting to explain this very remarkable fact have been put forward, but its real significance still remains unknown.^
5 Hon. R. J. Strutt : ** On the Tendency of the Atomic Weights to approximate to Whole Numbers," Philosophical Magazine [6], vol. i. (1901), pp. 311 et seq,
^ Two examples of these attempts must here suffice. Mr. A. C. G. Egerton ("The Divergence of the Atomic Weights of the Lighter Elements from Whole Numbers," Journal of the Chemical Societyy vol. xcv. pp. 238 et seq.y 1909) finds that the atomic weights (H=i) of the lighter elements (up to Phosphorus) can be calculated with considerable accuracy by means of the formulae —
(i) M = 2N ± 0*0078 X 2N and (ii) M = 2N 4- i ± 0*0078 X 2N,
where M is the atomic weight, and N the number of the element, reckoning Helium as 2, Lithium as 3, and so on, the elements being numbered in the order of their atomic weights. The first formula applies in the case of " even " elements, the second in the case of "odd" elements. For elements of higher atomic weight, similar but niore complicated formulae were found for those with atoms not heavier than Cobalt. Beyond Cobalt the method does not appear to be applicable. The author suggests that, since the figure 0*0078 represents approximately the weight of a group of eight electrons (see below, §§79 and 80), the elements may be built up of conglomerates of hydrogen atoms with groups of eight or sixteen electrons added or subtracted. But, as he remarks at the close of his paper (p. 242), " The physical interpretation of the relation given is evidently not the only one that can be devised. Since the ele- ments are built up by the conglomeration of the fundamental stuff, although not necessarily evolved in order of atomic weight, and since the atoms probably differ in internal structure, there are certain to be changes in the internal energy of the atoms causing slight differences in mass. One would expect such changes to be pro- portional to the increase of the amount of the original stuff which conglomerates ; the formula M = A ± A (0.0078) [A = 2NI agrees with this idea; and, further, it is conceivable that an increase in the size of an atom, due to addition of more matter, and the formation of a new atom, might either cause an increase or decrease of energy according to the configuration of the new atom ; the positive and negative sign in the formula might thus be explained."
§78] AGE OF MODERN CHEMISTRY 105
§ 78. A remarkable property of the atomic weights
was discovered, in the sixties, independently by
Lothar Meyer and Mendeleeff. They
The found that the elements could be
La^ » arranged in rows in the order of their
atomic weights so that similar elements
would be found in the same columns. A modernised
form of the Periodic Table will be found on pp. io6, 107.
It will be noticed, for example, that the "alkali'*
metals. Lithium, Sodium, Rubidium and Caesium, which
Dr. James Moir ("A Method of Harmonising the Atomic Weights,'* Journal of the Chemical Society^ vol. xcv. pp. 1752 et seq.^ 1909) criticises the above-mentioned paper. He assumes (p. 1752) "the cause of valency, at all events the fundamental valency of each element, to be the presence, in varying numbers, of a sub-element of atomic weight y^Tj- [= -0089] .... If this be denoted by /i, then the univalent elements contain i^, the bivalent 2/i, the tervalent 3/i, and so on. In addition, the author conceives the main bulk of the mass of the elements to be due to polymerisation of an entity consisting of the hydrogen atom less the aggregation /z. Denoting this by H, we have, for example: H = H-f-/ii; Li=7H-H/i; C = 12H + 4/ii ; O = 16H -f 2/i ; Ne = 20H ; Na = 23H -f /x ; Ag = 108H + fi ; Cs = 133H -I- /i." The atomic weights calcu- lated on these assumptions are in excellent agreement with the experimental. Thus —
H -h /* = H = 1-0078,
therefore
H = 1*0078 - '0089 — '9989. Li = 7H + /i = 7'ooi (Experimental value = 6'94) O = 16H 4" 2/i = 1 6'ooo (Experimental value = i6*oo) Ne = 20H = 19-978 (Experimental value = 20*2), &c.
However, there are some elements which do not fit into this scheme, and whose atomic weights can be calculated by this method only by employing multiples of H involving one decimal figure (for example, Chlorine and Sulphur), which elements the author regards as not being direct polymerides of H.
106
ALCHEMY
[§78
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Iron Fe =» 5585 Cobalt Co = 58-97 Nickel Ni = 58 68
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108 ALCHEMY [§ 78
resemble one another very closely, fall in Column i ; the "alkaline earth" metals occur together in Column 2 ; though in each case these are accompanied by certain elements with somewhat different properties. Much the same holds good in the case of the other columns of this Table ; there is manifested a remarkable regularity, with certain still more remarkable divergences (see notes appended to Table on pp. 106, 107). This regu- larity exhibited by the ** elements " is of considerable importance, since it shows that, in general, the pro- perties of the " elements " are periodic functions of their atomic weights ; and, together with certain other remarkable properties of the ** elements," distinguishes them sharply from the ** compounds." It may be concluded with tolerable certainty, therefore, that if the '* elements " are in reality of a compound nature, they are all, in general, compounds of a like nature distinct from that of other compounds.
It is now some years since Sir William Crookes first attempted to explain the periodicity of the properties of the elements on the theory that they have all been evolved by a conglomerating process from some primal stuff — the protyle — consisting of very small particles. He represents the action of this generative cause by means of a ** figure of eight " spiral, along which the elements are placed at regular intervals, so that similar elements come underneath one another, as in Mendeleeff s table, though the grouping difTers in some respects. The slope of the curve is supposed to represent the decline of some factor {e.g., tempera- ture) conditioning the process, which process is assumed to be of a recurrent nature, like the swing of a pendulum. After the completion of one swing
§ 79] AGE OF MODERN CHEMISTRY 109
(to keep to the Illustration of a pendulum) whereby one series of elements is produced, owing to the decline of the above-mentioned factor, the same series of elements is not again the result as would otherwise be the case, but a somewhat different series is pro- duced, each member of which resembles the corre- sponding member of the former series. Thus, if the first series contains, for example, helium, lithium, carbon, &c., the second series will contain instead, argon, potassium, titanium, &c. The whole theory, though highly interesting, is, however, by no means free from defects.
§ 79. We must now turn our attention to those recent views of the constitution of matter which
^ originated to a great extent in the in-
Corpuscular vestigations of the passage of electricity Theory of through gases at very low pressures. It
^ ®^' will be possible, however, on the present occasion, to give only the very briefest account of the subject; but a fuller treatment is rendered unnecessary by the fact that these and allied in- vestigations and the theories to which they have given rise have been fully treated in several well- known works, by various authorities on the subject, which have appeared during the last few years.7
When an electrical discharge is passed through a high-vacuum tube, invisible rays are emitted from the kathode, generally with the production of a greenish-
7 We have found Prof. Harry Jones' The Electrical Nature oj Matter and Radioactivity (1906), Mr. Soddy's Radioactivity (1904), and Mr. Whetham's The Recent Development of Physical Science (1909) particularly interesting. Mention, of course, should also be made of the standard works of Prof. Sir J. J. Thomson and Prof. Rutherford.
110 ALCHEMY [§ 80
yellow fluorescence where they strike the glass walls of the tube. These rays are called " kathode rays." At one time they were regarded as waves in the ether, but it was shown by Sir William Crookes that they consist of small electrically charged particles, moving with a very high velocity. Sir J. J. Thomson was able to determine the ratio of the charge carried by these particles to their mass or inertia ; he found that this ratio was constant whatever gas was contained in the vacuum tube, and much greater than the corre- sponding ratio for the hydrogen ion (electrically charged hydrogen atom) in electrolysis. By a skilful method, based on the fact discovered by Mr. C. T. R. Wilson, that charged particles can serve as nuclei for the condensation of water-vapour, he was further able to determine the value of the electrical charge carried by these particles, which was found to be constant also, and equal to the charge carried by univalent ions, e.g., hydrogen, in electrolysis. Hence, it follows that the mass of these kathode particles must be much smaller than the hydrogen ion, the actual ratio being about I : 1 700. The first theory put forward by Sir J. J. Thomson in explanation of these facts, was that these kathode particles (** corpuscles " as he termed them) were electrically charged portions of matter, much smaller than the smallest atom ; and since the same sort of corpuscle is obtained whatever gas is contained in the vacuum tube, it is reasonable to conclude that the corpuscle is the common unit of all matter.
§ 80. This eminent physicist, however, had shown mathematically that a charged particle moving with a very high velocity (approaching that of light)
§ 80] AGE OF MODERN CHEMISTRY 111
would exhibit an appreciable increase in mass or
inertia due to the charge, the magnitude of such inertia
depending on the velocity of the particle. This was
•n- r xr. X experimentallv verified by Kaufmann, Proof that ^ .,i ,.. 11
the Electrons who determmed the velocities, and the
are not ratios between the electrical char2:e and * ®^* the inertia, of various kathode particles and similar particles which are emitted by com- pounds of radium (see §§ 89 and 90). Sir J. J. Thomson calculated these values on the assumption that the inertia of such particles is entirely of electrical origin, and thereby obtained values in remarkable agreement with the experimental. There is, there- fore, no reason for supposing the corpuscle to be matter at all ; indeed, if it were, the above agreement would not be obtained. As Professor Jones says : ** Since we know things only by their properties, and since all the properties of the corpuscle are accounted for by the electrical charge associated with it, why assume that the corpuscle contains anything but the electrical charge? It is obvious that there is no reason for doing so.
** T/ie corpuscle isy then, nothing but a disembodied electrical charge, containing nothing material, as we have been accustomed to use that term. It is elec- tricity, and nothing but electricity. With this new conception a new term was introduced, and, now, instead of speaking of the corpuscle we speak of the electron''^ Applying this modification to the above view of the constitution of matter, we have what is called "the electronic theory," namely, that the
2 H. C. Jones : The Electrical Nature of Matter and Radioactivity (1906), p. 21.
112 ALCHEMY [§ 81
material atoms consist of electrons, or units of elec- tricity in rapid motion ; which amounts to this — that matter is simply an electrical phenomenon.
§ 81. Sir J. J. Thomson has elaborated this theory
of the nature and constitution of matter ; he has shown
what systems of electrons would be stable,
Electronic and has attempted to find therein the
Theory of significance of Mendeldeff's generalisa- ^ ®^* tion and the explanation of valency. There can be no doubt that there is a consider- able element of truth in the electronic theory of matter ; the one characteristic property of matter, i.e., inertia, can be accounted-for electrically; but further than this it is not yet possible to say. The fundamental difficulty is that the electrons are units of negative electricity, whereas matter is electrically neutral. Is there a positive electron? Professor Sir J. J. Thomson assumes a sphere or shell of positive electrification wherein the (negative) electrons re- volve ; and to this positive electricity, it seems, must be ascribed the major portion of the inertia or mass of the atom, for recent work has proved that the number of electrons in an atom is approximately equal to the atomic weight of that atom as expressed in terms of H = i or O = i6 as unit. This fact has rather discountenanced the corpuscular and electronic theories of matter, which as originally formulated assumed the whole mass of the atom to be due alone to corpuscles or electrons, and, therefore, required the atoms to contain thousands of such units ; but, as Pro- fessor Sir J. J. Thomson has pointed out, it is not really incompatible therewith, if, as does not seem unlikely, all mass Is really mass of the ether of space (see next
§ 82] AGE OF MODERN CHEMISTRY 113
section).9 The whole question, however, cannot be regarded as finally settled ; but it is hoped that further research will throw light on the disputed points.
§ 82. The analysis of matter has been carried a
step further. A philosophical view of the Cosmos
, involves the assumption of an absolutely
Etheric continuous and homogeneous medium Theory of filling all space, for an absolute * ®^' vacuum is unthinkable, and if it were supposed that the stuff filling all space is of an atomic structure, the question arises. What occupies the interstices between its atoms? This ubiquitous medium is termed by the scientists of to-day **the Ether of Space." Moreover, such a medium as the Ether is demanded by the phenomena of light. It appears, however, that the ether of space has another and a still more important function than the trans- mission of light : the idea that matter has its explana- tion therein is being developed by Sir Oliver Lodge. The evidence certainly points to the conclusion that matter is some sort of singularity in the ether, prob- ably a stress centre. We have been too much accustomed to think of the ether as something excessively light and quite the reverse of massive or dense, in which it appears we have been wrong. Sir Oliver Lodge calculates that the density of the ether is far greater than that of the most dense forms of matter ; not that matter is to be thought of as a rarefaction of the ether, for the ether within matter is as dense as that without. What we call matter, however, is not a continuous substance ; it consists,
9 See Professor Sir J. J. Thomson : The Corpuscular Theory of Matter (1907), especially pp. 142 et seq.
9
114 ALCHEMY [§ 83
rather, of a number of widely separated particles, whence its comparatively small density compared with the perfectly continuous ether. Further, if there is a difficulty in conceiving how a perfect fluid like the ether can give rise to a solid body possessed of such properties as rigidity, impenetrability and elasticity, we must remember that all these properties can be produced by means of motion. A jet of water moving with a sufficient velocity behaves like a rigid and im- penetrable solid, whilst a revolving disc of paper exhibits elasticity and can act as a circular saw.^^ It appears, therefore, that the ancient doctrine of the alchemistic essence is fundamentally true after all, that out of the ** One Thing " all material things have been produced by adaptation or modification ; and, as we have already noticed {§ 60), there also appears to be some resemblance between the concept of the electron and that of the seed of gold, which seed, it should be borne in mind, was regarded by the alchemists as the common seed of all metals.
§ 83. There are also certain other facts which
appear to demand such a modification of Dalton's
Atomic Theory as is found in the
Evidence Electronic Theory. One of the charac-
of the teristics of the chemical elements is that
Complexity each one gives a spectrum peculiar to
of the Atoms. . ,r ^^ ^ ^ 1 ^
Itself. The spectrum of an element
must, therefore, be due to its atoms, which in some
way are able, at a sufficiently high temperature,
to act upon the ether so as to produce vibrations of
definite and characteristic wave-length. Now, in
many cases the number of lines of definite wave-
^° See Sir Oliver Lodge, F.R.S. : T/ie Ether of Space (1909).
§85] AGE OF MODERN CHEMISTRY 115
length observed in such a spectrum is considerable, for example, hundreds of different lines have been observed in the arc-spectrum of iron. But it is in- credible that an atom, if it were a simple unit, would give rise to such a number of different and definite vibrations, and the only reasonable conclusion is that the atoms must be complex in structure. We may here mention that spectroscopic examination of various heavenly bodies leads to the conclusion that there is some process of evolution at work building up com- plex elements from simpler ones, since the hottest nebulae appear to consist of but a few simple elements, whilst cooler bodies exhibit a greater complexity.
§ 85. Such modifications of the atomic theory as those we have briefly discussed above, although profoundly modifying, and, indeed, con- Views of trovertinp^ the philosophical sis^nificance Ostwald. ^^ Dalton's theory as originally formu- lated, leave its chemical significance practically unchanged. The atoms can be regarded no longer as the eternal, indissoluble gods of Nature that they were once supposed to be ; thus, Materialism is deprived of what was thought to be its scientific basis. ^ I But the science of Chemistry is unaffected thereby ; the atoms are not the ultimate units out of which material things are built, but the atoms cannot be decomposed by purely chemical means ; the '* elements " are not truly elemental, but ^Aey are chemical elements. However, the atomic theory has been subjected to a far more searching criticism. Wald argues that substances obey the law of definite
" For a critical examination of Materialism, the reader is referred to the present writer's Matter^ Spirit and the Cosmos (Rider, 1910), especially Chapters I. and IV.
116 ALCHEMY [§ M
proportions because of the way in which they are prepared ; chemists refuse, he says, to admit any substance as a definite chemical compound unless it does obey this law. Wald's opinions have been supported by Professor Ostwald, who has attempted to deduce the other stoichiometric laws on these grounds without assuming any atomic hypothesis ^^ ; but these new ideas do not appear to have gained the approval of chemists in general. It is not to be supposed that chemists will give up without a struggle a mental tool of such great utility as Dalton's theory, in spite of its defects, has proved itself to be. There does seem, however, to be logic in the arguments of Wald and Ostwald, but it is too early in the history of the controversy to say what the ultimate result will be. So far as can be seen, however, it appears that, on the one hand, the atomic theory is not necessitated by the so-called "stoichiometric laws"; whilst, on the other hand, a molecular constitution of matter seems to be demanded by the phenomenon known as the " Brownian Movement," i.e., the spontaneous, irregular and apparently perpetual movement of microscopic portions of solid matter when immersed in a liquid medium ; such movement appearing to be explicable only as the result of the motion of the molecules of which the liquid in question is built up. ^3
" W. Ostwald : " Faraday Lecture," Journal of the Chemical Society, vol. Ixxxv. (1904), pp. 506 et seq. See also W. Ostwald: The Fundamental Principles of Chemistry (translated by H. W. Morse, 1909), especially Chapters VI., VII. and VIII.
^3 For an account of this singular phenomenon, see Prof. Jean Perrin : Brownian Movement and Molecular Reality (translated from the Annates de Chimie et de Physique, 8me Series, September, 1909, by F. Soddy, M.A., F.R.S., 1910).