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 Beccherianæ, 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 shown 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. burgh, but a young man of the age of twenty-four at the time when he made his discovery. 2 He found that the difference between caustic lime and common limestone arose from this, that the latter substance consists of the former, combined with a certain air, which, being thus fixed in the solid body, he called fixed air (carbonic acid gas). He found, too, that magnesia, caustic potash, and caustic soda, would combine with the same air, with similar results. This discovery consisted, of course, in a new interpretation of observed changes. Alkalies appeared to be made caustic by contact with quicklime at first Black imagined that they underwent this change by acquiring igneous matter from the quicklime; but when he perceived that the lime gained, not lost, in magnitude as it became mild, he rightly supposed that the alkalies were rendered caustic by imparting their air to the lime. This discovery was announced in Black's inaugural dissertation, pronounced in 1755, on the occasion of his taking his degree of Doctor in the University of Edinburgh. The chemistry of airs was pursued by other experimenters. The Honourable Henry Cavendish, about 1765, invented an apparatus, in which aërial fluids are confined by water, so that they can be managed and examined. This hydro-pneumatic apparatus, or, as it is sometimes called, the pneumatic trough, from that time was one of the most indispensable parts of the chemist's apparatus. Cavendish,3 in 1766, showed the identity of the properties of fixed air derived from various sources; and pointed out the peculiar qualities of inflammable air (afterwards called hydrogen gas), which, being nine times lighter than common air, soon attracted general notice by its employment for raising balloons. The promise of discovery which this subject now offered, attracted the confident and busy mind of Priestley, whose Experiments and Observations on different kinds of Air appeared in 1744-79. In these volumes, he describes an extraordinary number of trials of various kinds; the results of which were, the discovery 2 Thomson's Hist. Chem. i. 317. 3 Phil. Trans. 1706. of new kinds of air, namely, phlogisticated air (azotic gas), nitrous air (nitrous gas), and dephlogisticated air (oxygen gas). But the discovery of new substances, though valuable in supplying chemistry with materials, was not so important as discoveries respecting their modes of composition. Among such discoveries, that of Cavendish, published in the Philosophical Transactions for 1784, and disclosing the composition of water by the union of two gases, oxygen and hydrogen, must be considered as holding a most distinguished place. He states,1 that 'his experiments were made principally with a view to find out the cause of the diminution which common air is well known to suffer, by all the various ways in which it is phlogisticated.' And, after describing various unsuccessful attempts, he finds that when inflammable air is used in this phlogistication (or burning), the diminution of the common air is accompanied by the formation of a dew in the apparaAnd thus he infers that almost all the inflammable air, and one-fifth of the common air, are turned into pure water.' tus. 5 Lavoisier, to whose researches this result was, as we shall soon see, very important, was employed in a similar attempt at the same time (1783), and had already succeeded, when he learned from Dr. Blagden, who was present at the experiment, that Cavendish had made the discovery a few months sooner. Monge had, about the same time, made the same experiments, and communicated the result to Lavoisier and Laplace immediately afterwards. The synthesis was soon confirmed by a corresponding analysis. Indeed the discovery undoubtedly lay in the direct path of chemical research at the time. It was of great consequence in the view it gave of experiments in composition; for the small quantity of water produced in many such processes, had been quite overlooked; though, as it Phil. Trans. 1784, p, 119. 5 [b. 6 Ib. p. 129. |