CHAPTER II

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DOCTRINE OF ACID AND ALKALI.--SYLVIUS.

AMONG the results of mixture observed by chemists, were many instances in which two ingredients, each in itself pungent or destructive, being put together, became mild and inoperative; each {263} counteracting and neutralizing the activity of the other. The notion of such opposition and neutrality is applicable to a very wide range of chemical processes. The person who appears first to have steadily seized and generally applied this notion is Francis de la Boé Sylvius; who was born in 1614, and practised medicine at Amsterdam, with a success and reputation which gave great currency to his opinions on that art.[2\14] His chemical theories were propounded as subordinate to his medical doctrines; and from being thus presented under a most important practical aspect, excited far more attention than mere theoretical opinions on the composition of bodies could have done. Sylvius is spoken of by historians of science, as the founder of the _iatro-chemical_ sect among physicians; that is, the sect which considers the disorders in the human frame as the effects of chemical relations of the fluids, and applies to them modes of cure founded upon this doctrine. We have here to speak, not of his physiological, but of his chemical views.

[Note 2\14: Sprengel. _Geschichte der Arzneykunde_, vol. iv. Thomson's _History of Chemistry_ in the corresponding part is translated from Sprengel.]

The distinction of _acid_ and _alkaline_ bodies (_acidum_, _lixivum_) was familiar before the time of Sylvius; but he framed a system, by considering them both as eminently acrid and yet opposite, and by applying this notion to the human frame. Thus[3\14] the lymph contains an acid, the bile an alkaline salt. These two opposite acrid substances, when they are brought together, _neutralize_ each other (_infringunt_), and are changed into an intermediate and milder substance.

[Note 3\14: _De Methodo Medendi_, Amst. 1679. Lib. ii. cap. 28, sects. 8 and 53.]

The progress of this doctrine, as a physiological one, is an important part of the history of medical science in the seventeenth century; but with that we are not here concerned. But as a chemical doctrine, this notion of the opposition of acid and alkali, and of its very general applicability, struck deep root, and has not been eradicated up to our own time. Boyle, indeed, whose disposition led him to suspect all generalities, expressed doubts with regard to this view;[4\14] and argued that the supposition of acid and alkaline parts in all bodies was precarious, their offices arbitrary, and the notion of them unsettled. Indeed it was not difficult to show, that there was no one certain criterion to which all supposed acids conformed. Yet the general conception of such a combination as that of acid and alkali was supposed to {264} be, served so well to express many chemical facts, that it kept its ground. It is found, for instance, in Lemery's _Chemistry_, which was one of those in most general use before the introduction of the phlogistic theory. In this work (which was translated into English by Keill, in 1698) we find alkalies defined by their effervescing with acids.[5\14] They were distinguished as the _mineral_ alkali (soda), the _vegetable_ alkali (potassa), and the _volatile_ alkali (ammonia). Again, in Macquer's _Chemistry_, which was long the text-book in Europe during the reign of phlogiston, we find acids and alkalies, and their union, in which they rob each other of their characteristic properties, and form neutral salts, stated among the leading principles of the science.[6\14]

[Note 4\14: Shaw's _Boyle_, iii. p. 432.]

[Note 5\14: Lemery, p. 25.]

[Note 6\14: Macquer, p. 19.]

In truth, the mutual relation of acids to alkalies was the most essential part of the knowledge which chemists possessed concerning them. The importance of this relation arose from its being the first distinct form in which the notion of chemical attraction or affinity appeared. For the acrid or caustic character of acids and alkalies is, in fact, a tendency to alter the bodies they touch, and thus to alter themselves; and the neutral character of the compounds **is the absence of any such proclivity to change. Acids and alkalies have a strong disposition to unite. They combine, often with vehemence, and produce neutral salts; they exhibit, in short, a prominent example of the chemical attraction, or affinity, by which two ingredients are formed into a compound. The relation of _acid_ and _base_ in a salt is, to this day, one of the main grounds of all theoretical reasonings.

The more distinct development of the notion of such chemical attraction, gradually made its way among the chemists of the latter part of the seventeenth and the beginning of the eighteenth century, as we may see in the writings of Boyle, Newton, and their followers. Beecher speaks of this attraction as a _magnetism_; but I do not know that any writer in particular, can be pointed out as the person who firmly established the general notion of _chemical attraction_.

But this idea of chemical attraction became both more clear and more extensively applicable, when it assumed the form of the doctrine of _elective_ attractions, in which shape we must now speak of it. {265}

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