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by virtue of a reaction between it and the metallic nitrate, whereby nitric acid is continually reproduced in the solution. If this is really the case, then it may very well be that formation of hydroxylamine is increased by the simultaneous production, within the sphere of mutual action, of hydrogen and nitric acid, i.e. by the presence in the solution of nascent hydrogen and nascent nitric acid. The nature of the second acid, as might be expected, is an important factor in the change: the amount of water present, and the temperature at various stages of the reaction also exert marked influence on the final result.

45. The expression 'nascent action' has probably been at once helpful and harmful to the progress of chemistry. By classing under a common name many phenomena that might otherwise have been lost in the vast mass of facts with which the science has to deal, the expression has, I think, done good service; but in so far as its use has tended to prevent investigation-for it is always easier to say of any unusual reactions, 'these are cases of nascent action 'than to examine carefully into their course and conditions-and also in so far as it has favoured the impression that “nascent' hydrogen or ‘nascent' oxygen, &c. is ordinary hydrogen or oxygen, &c. with certain indefinite properties which are always attached to the hydrogen, or other element, when in this peculiar condition, the use of the expression has, I think, been unfavourable to the best interests of chemical science.

A study of the reactions in which nascent substances play important parts appears to me to keep before the student that all-important distinction between the atom and the molecule which is so vital in chemical considerations, and also to draw attention in a marked way to the complexity of all chemical changes. We find, or think we find, that when atoms of hydrogen are presented to another substance in a given chemical reaction, certain definite products result; and we are apt to conclude that the action of hydrogen atoms on this substance will always give this result; but investigation discovers that not only the course of the reaction, but also the final configuration of the changing system, is dependent on

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the whole previous history of the reacting bodies. Hydrogen as it is produced by the action of sodium-amalgam appears to possess properties different from those which characterise hydrogen produced by the action of zinc on dilute sulphuric acid ; attempts to explain these apparent differences lead to fresh researches; we become impressed with the conviction that chemistry is not the study of this element or that, regarded as a kind of matter with certain fixed physical properties, but that processes of change are the subject-matter of the science, and that to explain any one of these we must take into account each and all of the reacting bodies, and each and all of the conditions under which the total change is proceeding.

If the expression ‘nascent action' does in any way help to emphasise such considerations as these, I think it ought to be retained in chemical nomenclature.

SECTION II. The Dualistic and Unitary Theories.

46. Partly from his definition of element, partly from his study of the products of combustion in oxygen, of phosphorus, carbon, sulphur, &c., Lavoisier was led to regard every salt as formed by the union of an acid with a radicle, the latter being itself either simple or compound.

Davy began his electro-chemical researches in the early years of the present century. In the Philosophical Transactions for 1807', and in his Elements of Chemical Philosophy, he regards chemical combination as accompanied by an exchange of quantities of electricity of opposite sign between the combining bodies. He found that when sulphur and copper are rubbed together the sulphur is negatively, the copper positively, electrified; and that when the sulphur is heated the electrical activities become more apparent, until the sulphur melts, when chemical combination occurs and the product, copper sulphide, exhibits neither positive or

1 'On some chemical agencies of electricity,' p. 1.

? Collected works, vol. iv. (see also Ladenburg's Entwickelungsgeschichte der Chemie, pp. 75–81).

negative electricity. If the quantity of electricity lost in the act of chemical union is restored, e.g. by the passage of a current through the compound formed, chemical decomposition occurs and the original components are again obtained. Davy regarded the primary cause of chemical and electrical effects as possibly the same force; when this force is exerted between masses of matter electrical phenomena result; when it is exerted between the smallest particles of bodies chemical phenomena result. Thus in his Elements of Chemical Philosophy Davy says, Electrical effects are ex'hibited by the same bodies when acting as masses, which "produce chemical phenomena when acting by their particles; it is not therefore improbable that the primary cause of both 'may be the same, and that the same arrangements of matter, 'or the same attracting powers, which place bodies in the relations of positive and negative, i.e. which render them 'attractive of each other electrically, and capable of com'municating attractive powers to other matter, may likewise 'render their particles attractive, and enable them to combine, 'when they have full freedom of motion.' "That the de'composition of the chemical agents is connected with the 'energies of the pile, is evident from all the experiments that have been made; as yet no sound objection has been urged ' against the theory that the contact of the metals destroys 'the electrical equilibrium, and that the chemical changes 'restore it; and, in consequence, that the action exists as long 'as the decompositions continue?'

47. At once a brilliant theoriser and a thorough-going experimenter, Davy did not attempt to found a general scheme of chemical classification on his electro-chemical work. This was however done by Berzelius, who developed a consistent and definite, although narrow theory which for a time seemed to explain all chemical phenomena.

1 Loc. cit. pp. 119-120, and p. 125.

? It is interesting to observe how similar this view, stated by Davy in the beginning of the present century, is to the latest views regarding the connection of chemical and electrical forces. Compare especially Helmholtz's 'Faraday Lecture.' (C. S. Journal Trans. for 1881, 277 et seq: see particularly pp. 300—30 2.) [See post, Book II. ]

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All chemical actions were regarded by Berzelius as brought about by electrical force'. Die Elektricität...scheint die erste 'Thätigkeits-Ursache in der ganzen, uns umgebenden Natur zu 'sein.' Electrical actions, according to Berzelius, were not to be described as consequences of contact, or of mutual action between heterogeneous bodies. Each elementary atom, he held, is endowed with two kinds of electricity, it has two electric poles; but these poles differ in strength, so that each atom considered as whole is characterised positively or negatively electrified; in some elementary atoms positive electricity predominates and gives a positive character to the whole atom ; in others negative electricity overpowers the positive. When a positively electrified atom attracts a negatively electrified atom, opposite electricities neutralise one another, but the electricities formerly masked in the separate atoms now come into play, and so the new group of atoms, as a whole, exhibits positive or negative electricity, in virtue of which it is capable of chemically combining with other atoms or groups of atoms. But as the stronger poles are first neutralised, it follows that the more complex a compound is, the less polarity does it exhibit, and hence the less readily does it combine with other substances. Berzelius moreover regarded the quantity of electricity on either pole as to some extent variable with variations of temperature. On the Berzelian theory atoms are regarded as essentially unipolar; one polarity so predominates over the other that each atom acts as a positively or negatively electrified whole.

The electro-chemical properties of oxidised compounds, Berzelius taught, depend chiefly on the unipolarity of the electro-positive radicles they contain. Of two oxides, that which contains the more electro-negative radicle is generally itself electro-negative; thus sulphuric acid (regarded as SO) is electro-negative to all metallic oxides, because sulphur is itself electro-negative to all metals ; on the other hand the oxides of potassium and sodium are electro-positive to all other oxides (excepting those of cæsium and rubidium) be

1 Lehrbuch (1st Ed.), III. part 1. p. 77.

cause potassium and sodium are themselves electro-positive to all other elements' (except cæsium and rubidium).

Polarity and chemical affinity are closely connected in the system of Berzelius: the 'specific unipolarity'? however does not alone determine the greater or less affinity of one atom for another. Some atoms have a more intense polarity than others and therefore exhibit a greater striving (Bestreben') to neutralise the electricity divided between their poles, in other words, have a greater affinity for a given substance than other atoms.

Chemical affinity appears to have been regarded by Berzelius as nearly synonymous with intensity of atomic polarity:. Thus, oxygen combines with sulphur rather than with lead, although oxygen and sulphur have the same unipolarity (viz. negative); but, the Berzelian view asserts, the positive pole of the sulphur atom neutralises more negative electricity on the oxygen atom than can be neutralised by the positive pole of the lead atom.

Double decompositions were readily explained in terms of this theory: 'Every chemical action,' says Berzelius“, ‘is an 'electrical phenomenon depending on the electrical polarity of the particles; everything that appears to be due to the 'action of affinity is caused by the possession by some bodies ‘of an electrical polarity stronger than that of others. If the 'compound AB is decomposed by the substance C which has

a greater affinity for A than B has, then C must possess a 'more intense electrical polarity than B; on this account 'there results more complete neutralisation between A and C 'than between A and B.... If two bodies, AB and CD, so

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1 An important deduction made from these considerations is, that as oxygen occurs both in markedly electro-positive and electro-negative compounds, and as acids are as a group electro-negative, oxygen cannot be the acidifying element, as Lavoisier said it was.

? Specifische Unipolarität. Berzelius, loc. cit. p. 73.

3 This might perhaps be regarded as equivalent to the modern conception of higher and lower potential; as if one atom might have a smaller electrical charge but at a higher potential than another, and would therefore exhibit greater chemical affinity than the other.

4 Lehrbuch (ist Ed.), 111. part I. p. 77.

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