CHAPTER IV

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DOCTRINE OF ACIDIFICATION AND COMBUSTION.--PHLOGISTIC THEORY.

PUBLICATION _of the Theory by Beccher and Stahl._--It will be recollected that we are tracing the history of the _progress_ only of Chemistry, not of its errors;--that we are concerned with doctrines only so far as they are true, and have remained part of the received system of chemical truths. The Phlogistic Theory was deposed and succeeded by the Theory of Oxygen. But this circumstance must not lead us to overlook the really sound and permanent part of the opinions which the founders of the phlogistic theory taught. They brought together, as processes of the same kind, a number of changes which at first appeared to have nothing in common; as acidification, combustion, respiration. Now this classification is true; and its importance remains undiminished, whatever are the explanations which we adopt of the processes themselves.

The two chemists to whom are to be ascribed the merit of this step, and the establishment of the _phlogistic theory_ which they connected {268} with it, are John Joachim Beccher and George Ernest Stahl; the former of whom was professor at Mentz, and physician to the Elector of Bavaria (born 1625, died 1682); the latter was professor at Halle, and afterwards royal physician at Berlin (born 1660, died 1734). These two men, who thus contributed to a common purpose, were very different from each other. The first was a frank and ardent enthusiast in the pursuit of chemistry, who speaks of himself and his employments with a communicativeness and affection both amusing and engaging. The other was a teacher of great talents and influence, but accused of haughtiness and moroseness; a character which is well borne out by the manner in which, in his writings, he anticipates an unfavorable reception, and defies it. But it is right to add to this that he speaks of Beccher, his predecessor, with an ungrudging acknowledgment of obligations to him, and a vehement assertion of his merit as the founder of the true system, which give a strong impression of Stahl's justice and magnanimity.

Beccher's opinions were at first promulgated rather as a correction than a refutation of the doctrine of the three principles, salt, sulphur, and mercury. The main peculiarity of his views consists in the offices which he ascribes to his _sulphur_, these being such as afterwards induced Stahl to give the name of _Phlogiston_ to this element. Beccher had the sagacity to see that the reduction of metals to an earthy form (_calx_), and the formation of sulphuric acid from sulphur, are operations connected by a general analogy, as being alike processes of combustion. Hence the metal was supposed to consist of an earth, and of something which, in the process of combustion, was separated from it; and, in like manner, sulphur was supposed to consist of the sulphuric acid, which remained after its combustion, and of the combustible part or true sulphur, which flew off in the burning. Beccher insists very distinctly upon this difference between his element sulphur and the "sulphur" of his Paracelsian predecessors.

It must be considered as indicating great knowledge and talent in Stahl, that he perceived so clearly what part of the views of Beccher was of general truth and permanent value. Though he[11\14] everywhere gives to Beccher the credit of the theoretical opinions which he promulgates, ("Beccheriana sunt quæ profero,") it seems certain that he had the merit, not only of proving them more completely, and applying them more widely than his forerunner, but also of conceiving them {269} with a distinctness which Beccher did not attain. In 1697, appeared Stahl's _Zymotechnia Fundamentalis_ (the Doctrine of Fermentation), "simulque _experimentum novum_ sulphur verum arte producendi." In this work (besides other tenets which the author considered as very important), the opinion published by Beccher was now maintained in a very distinct form;--namely, that the process of forming sulphur from sulphuric acid, and of restoring the metals from their calces, are analogous, and consist alike in the addition of some combustible element, which Stahl termed _phlogiston_ (φλογίστον, _combustible_). The experiment most insisted on in the work now spoken of,[12\14] was the formation of sulphur from sulphate of potass (or of soda) by fusing the salt with an alkali, and throwing in coals to supply phlogiston. This is the "experimentum novum." Though Stahl published an account of this process, he seems to have regretted his openness. "He denies not," he says, "that he should peradventure have dissembled this experiment as the true foundation of the Beccherian assertion concerning the nature of sulphur, if he had not been provoked by the pretending arrogance of some of his contemporaries."

[Note 11\14: **Stahl, _Præf. ad Specim. Becch._ 1703.]

[Note 12\14: P. 117.]

From this time, Stahl's confidence in his theory may be traced becoming more and more settled in his succeeding publications. It is hardly necessary to observe here, that the explanations which his theory gives are easily transformed into those which the more recent theory supplies. According to modern views, the addition of oxygen takes place in the formation of acids and of calces, and in combustion, instead of the subtraction of phlogiston. The coal which Stahl supposed to supply the combustible in his experiment, does in fact absorb the liberated oxygen. In like manner, when an acid corrodes a metal, and, according to existing theory, combines with and oxidates it, Stahl supposed that the phlogiston separated from the metal and combined with the acid. That the explanations of the phlogistic theory are so generally capable of being translated into the oxygen theory, merely by inverting the supposed transfer of the combustible element, shows us how important a step towards the modern doctrines the phlogistic theory really was.

The question, whether these processes were in fact addition or subtraction, was decided by the balance, and belongs to a succeeding period of the science. But we may observe, that both Beccher and Stahl were aware of the increase of weight which metals undergo in {270} calcination; although the time had not yet arrived in which this fact was to be made one of the bases of the theory.

It has been said,[13\14] that in the adoption of the phlogistic theory, that is, in supposing the above-mentioned processes to be addition rather than subtraction, "of two possible roads the wrong was chosen, as if to prove the perversity of the human mind." But we must not forget how natural it was to suppose that some part of a body was _destroyed_ or _removed_ by combustion; and we may observe, that the merit of Beccher and Stahl did not consist in the selection of one road or two, but in advancing so far as to reach this point of separation. That, having done this, they went a little further on the wrong line, was an error which detracted little from the merit or value of the progress really made. It would be easy to show, from the writings of phlogistic chemists, what important and extensive truths their theory enabled them to express simply and clearly.

[Note 13\14: Herschel's _Introd. to Nat. Phil._ p. 300.]

That an enthusiastic temper is favorable to the production of great discoveries in science, is a rule which suffers no exception in the character of Beccher. In his preface[14\14] addressed "to the benevolent reader" of his _Physica Subterranea_, he speaks of the chemists as a strange class of mortals, impelled by an almost insane impulse to seek their pleasure among smoke and vapor, soot and flame, poisons and poverty. "Yet among all these evils," he says, "I seem to myself to live so sweetly, that, may I die if I would change places with the Persian king." He is, indeed, well worthy of admiration, as one of the first who pursued the labors of the furnace and the laboratory, without the bribe of golden hopes. "My kingdom," he says, "is not of this world. I trust that I have got hold of my pitcher by the right handle,--the true method of treating this study. For the _Pseudochymists_ seek gold; but the _true philosophers_, science, which is more precious than any gold."

[Note 14\14: Frankfort, 1681.]

The _Physica Subterranea_ made no converts. Stahl, in his indignant manner, says,[15\14] "No one will wonder that it never yet obtained a physician or a chemist as a disciple, still less as an advocate." And again, "This work obtained very little reputation or estimation, or, to speak ingenuously, as far as I know, none whatever." In 1671, Beccher published a supplement to his work, in which he showed how metal might be extracted from mud and sand. He offered to execute {271} this at Vienna; but found that people there cared nothing about such novelties. He was then induced, by Baron D'Isola, to go to Holland for similar purposes. After various delays and quarrels, he was obliged to leave Holland for fear of his creditors; and then, I suppose, came to Great Britain, where he examined the Scottish and Cornish mines. He is said to have died in London in 1682.

[Note 15\14: Præf. _Phys. Sub._ 1703.]

Stahl's publications appear to have excited more notice, and led to controversy on the "so-called sulphur." The success of the experiment had been doubted, which, as he remarks, it was foolish to make a matter of discussion, when any one might decide the point by experiment; and finally, it had been questioned whether the substance obtained by this process were pure sulphur. The originality of his doctrine was also questioned, which, as he says, could not with any justice be impugned. He published in defence and development of his opinion at various intervals, as the _Specimen Beccherianum_ in 1703, the _Documentum Theoriæ Beecherianæ_, a Dissertation _De Anatomia Sulphuris Artificialis_; and finally, _Casual Thoughts on the so-called Sulphur_, in 1718, in which he gave (in German) both a historical and a systematic view of his opinions on the nature of salts and of his Phlogiston.

_Reception and Application of the Theory._--The theory that the formation of sulphuric acid, and the restoration of metals from their calces, are analogous processes, and consist in the addition of _phlogiston_, was soon widely received; and the Phlogistic School was thus established. From Berlin, its original seat, it was diffused into all parts of Europe. The general reception of the theory may be traced, not only in the use of the term "phlogiston," and of the explanations which it implies; but in the adoption of a nomenclature founded on those explanations, which, though not very extensive, is sufficient evidence of the prevalence of the theory. Thus when Priestley, in 1774, discovered oxygen, and when Scheele, a little later, discovered chlorine, these gases were termed _dephlogisticated air_, and _dephlogisticated marine acid_; while azotic acid gas, having no disposition to combustion, was supposed to be saturated with phlogiston, and was called _phlogisticated air_.

This phraseology kept its ground, till it was expelled by the antiphlogistic, or oxygen theory. For instance. Cavendish's papers on the chemistry of the airs are expressed in terms of it, although his researches led him to the confines of the new theory. We must now give an account of such researches, and of the consequent revolution in the science. {272}

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