pally, to their facility of combination with oxygen. Thus, the First Section is the Metals of the Earths; the Second, the Metals of the Alkalies; the Third, the Easily Oxidable Metals, as Iron; the Fourth, Metals Less Oxidable, as Copper and Lead; the Fifth Section contains only Mercury and Osmium; and the Sixth, what were at an earlier period termed the Noble Metals, Gold, Silver, Platinum, and others. How such principles are to be applied, so as to produce a definite and consistent arrangement, will be explained in speaking of the philosophy of the Classificatory Sciences; but there are one or two peculiarities in the classes of bodies thus recognized by modern chemistry, which it may be useful to notice. 1. The distinction of Metallic and Non-metallic is still employed, as of fundamental importance. The discovery of new metals is so much connected with the inquiries concerning chemical elements, that we may notice the general progress of such discoveries. Gold, Silver, Iron, Copper, Quicksilver, Lead, Tin, were known from the earliest antiquity. In the beginning of the sixteenth century, mine-directors, like George Agricola, had advanced so far in practical metallurgy, that they had discovered the means of extracting three additional metals, Zinc, Bismuth, Antimony. After this, there was no new metal discovered for a century, and then such discoveries were made by the theoretical chemists, a race of men who had not existed before Beccher and Stahl. Thus Arsenic and Cobalt were made known by Brandt, in the middle of the eighteenth century, and we have a long list of similar discoveries belonging to the same period; Nickel, Manganese, and Tungsten, which were detected by Cronstedt, Gahn, and Scheele, jand Delhuyart, respectively; metals of a very different kind, Tellurium and Molybdenum, which were brought to light by Müller, Scheele, Bergman, and Hielm; Platinum, which was known as early as 1741, but with the ore of which, in 1802 and 1803, the English chemists, Wollaston and Tennant, found that no less than four other new metals (Palladium, Rhodium, Iridium and Osmium) were associated. Finally, (omitting some other new metals,) we have another period of discovery, opened in 1807, by Davy's discovery of Potassium, and including the resolution of all, or almost all, the alkalies and earths into metallic bases. [2nd Ed.] [The next few years made some, at least some conjectural, additions to the list of simple substances, detected by a more minute scrutiny of known substances. Thorium was discovered by Berzelius in 1828; and Vanadium by Professor Sefström in 1830. A metal named Cerium, was discovered in 1803, by Hisinger and Berzelius, in a rare Swedish mineral known by the name of Cerit. Mosander more recently has found combined with Cerium, other new metals, which he has called Lanthanium, Didymium, Erbium, and Terbium: M. Klaus has found a new metal, Ruthenium, in the ore of Platinum ; and Rose has discovered in Tantalite two other new metals, which he has announced under the names of Pelopium and Niobium. Svanberg is said to have discovered a new earth in Eudialyt, which is sup posed to have, like the rest, a new radical. If these last discoveries be confirmed, the number of simple substances will be raised to sixtytwo.] 2. Attempts have been made to indicate the classification of chemical substances by some peculiarity in the Name; and the Metals, for example, have been designated generally by names in um, like the Latin names of the ancient metals, aurum, ferrum. This artifice is a convenient nomenclature for the purpose of marking a recognized difference; and it would be worth the while of chemists to agree to make it universal, by writing molybdenum and platinum; which is sometimes done, but not always. 3. I am not now to attempt to determine how far this class,— Metals, extends; but where the analogies of the class cease to hold, there the nomenclature must also change. Thus, some chemists, as Dr. Thomson, have conceived that the base of Silica is more analogous to Carbon and Boron, which form acids with oxygen, than it is to the metals: and he has accordingly associated this base with these substances, and has given it the same termination, Silicon. But on the validity of this analogy chemists appear not to be generally agreed. 4. There is another class of bodies which have attracted much notice among modern chemists, and which have also been assimilated to each other in the form of their names; the English writers calling them Chlorine, Fluorine, Iodine, Bromine, while the French use the terms Chlore, Phtore, Iode, Brome. We have already noticed the establishment of the doctrine-that muriatic acid is formed of a base, chlorine, and of hydrogen,-as a great reform in the oxygen theory; with regard to which rival claims were advanced by Davy, and by MM. Gay-Lussac and Thenard in 1809. Iodine, a remarkable body which, from a dark powder, is converted into a violet-colored gas by the application of heat, was also, in 1813, the subject of a similar rivalry between the same English and French chemists. Bromine was only discovered as late as 1826; and Fluorine, or Phtore, as, from its destructive nature, it has been proposed to term it, has not been obtained as a separate substance, and is inferred to exist by analogy only. The analogies of these bodies (Chlore, Phtore, &c.) are very peculiar; for instance, by combination with metals they form salts; by combination with hydrogen they form very strong acids; and all, at the common temperature of the atmosphere, operate on other bodies in the most energetic manner. Berzelius proposes to call them halogenous bodies, or halogenes. 3 5. The number of Elementary Substances which are at present presented in our treatises of chemistry' is fifty-three, [or rather, as we have said above, sixty-two.] It is naturally often asked what evidence we have, that all these are elementary, and what evidence that they are all the elementary bodies;-how we know that new elements may not hereafter be discovered, or these supposed simple bodies resolved into simpler still? To these questions we can only answer, by referring to the history of chemistry;-by pointing out what chemists have understood by analysis, according to the preceding narrative. They have considered, as the analysis of a substance, that elementary constitution of it which gives the only intelligible explanation of the results of chemical manipulation, and which is proved to be complete as to quantity, by the balance, since the whole can only be equal to all its parts. It is impossible to maintain that new substances may not hereafter be discovered; for they may lurk, even in familiar substances, in doses so minute that they have not yet been missed amid the inevitable slight inaccuracies of all analysis; in the way in which iodine and bromine remained so long undetected in sea-water; and new minerals, or old ones not yet sufficiently examined, can hardly fail to add something to our list. As to the possibility of a further analysis of our supposed simple bodies, we may venture to say that, in regard to such supposed simple bodies as compose a numerous and well-characterized class, no such step can be made, except through some great change in chemical theory, which gives us a new view of all the general relations which chemistry has yet discovered. The proper evidence of the reality of any supposed new analysis is, that it is more consistent with the known analogies of chemistry, to suppose the process analytical than synthetical. Thus, as has already been said, chemists admit the existence of fluorine, from the analogy of chlorine; and Davy, when it was found 3 Chem. i. 262. 4 Turner, p. 971. that ammonia formed an amalgam with mercury, was tempted to assign to it a metallic basis. But then he again hesitates," and doubts whether the analogies of our knowledge are not better preserved by supposing that ammonia, as a compound of hydrogen and another principle, is "a type of the composition of the metals." Our history, which is the history of what we know, has little to do with such conjectures. There are, however, some not unimportant principles which bear upon them, and which, as they are usually employed, belong to the science which next comes under our review, Mineralogy. Elem. Chem. Phil. 1812, p. 481. |