(besides other tenets which the author considered as very important), the opinion published by Beccher was now maintained in a very distinct form;-naïnely, 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 (pλoziorov, combustible). The experiment most insisted on in the work now spoken of, 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 almost 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.'

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 the 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

2 P. 117.

The question whether these processes were in fact salition or su traction, 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 calcitation; 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 that in the adoption of the phlogistic theory, that is, in supposing the abovementioned 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 naust 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 errour 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.

That an enthusiastic temper is favourable to the production of great discoveries in science, is a rule which suffers no exception in the character of Beecher. In his preface 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 vapour, 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

3 Herschel's Introd. to Nat. Phil. p. 300.

4 Frankfort, 1681.

admiration, as one of the first who pursued the labours 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.'

The Physica Subterranea made no converts. Stahl, in his indignant manner, says,5 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 metals might be extracted from mud and sand. He offered to execute 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.

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 Theoria Beccheriana, a Dissertation De Anatomia Sulphuris Artificialis; and finally, Casual Thoughts on

Præf. Phys. Sub. 1703.

the so-called Sulphur, in 1718, in which he gave (in German) both an 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.

CHAPTER V.

CHEMISTRY OF GASES.-BLACK. CAVENDISH.

THE study of the properties of aëriform substances, or Pneumatic Chemistry, as it was called, occupied the chemists of the eighteenth century, and was the main occasion of the great advances which the science made at that period. The most material general truths which came into view in the course of these researches, were, that gases were to be numbered among the constituent elements of solid and fluid bodies; and that, in these, as in all other cases of composition, the compound was equal to the sum of its elements. The latter proposition, indeed, cannot be looked upon as a discovery, for it had been frequently acknowledged, though little applied; in fact, it could not be referred to with any advantage, till the aëriform elements, as well as others, were taken into the account. As soon as this was done, it produced a revolution in chemistry.

[2nd Ed.] [Though the view of the mode in which gaseous elements become fixed in bodies and determine their properties, had great additional light thrown upon it by Dr. Black's discoveries, as we shall see, the notion that solid bodies involve such gaseous elements was not new at that period. Mr. Vernon Harcourt has shown1 that Newton and Boyle admitted into their speculations airs of various kinds, capable of fixation in bodies. I have, in the succeeding chapter, (Chap. vi.) spoken of the views of Rey, Hooke and Mayow, connected with the function of airs in chemistry, and forming a prelude to the Oxygen Theory.]

Notwithstanding these preludes, the credit of the first great step in pneumatic chemistry is, with justice, assigned to Dr. Black, afterwards professor at Edin

Phil. Mag. 1846.