practical skill which the Swedish assayers, from before the time when Stahl used the blowpipe in 1700, had been gradually accumulating, and of which Bergman, with the assistance of Gahn, then his pupil, had already published a synopsis in the second volume of his Chemical Essays.'* The filial spirit of a grateful scholar appeared in what we have heard Berzelius say, long after Gahn's death, about his own book on the blowpipe: Most of what I have recorded there I learned 'from Gahn; I have only put it into my own words.' Of late years this branch of inquiry has also received great extension; and the work of Plattner (Die Probirkunst mit dem Löthrohr'), which has been done into English by Dr. Muspratt, is now a standard authority. Within the domain of inorganic chemistry, yet another field of vast extent is now undergoing the operation of clearing. To speak in the language of a North American settler, the trees are partially cut down; a few have already been burned; the first seed has been sown upon the spread ashes; and the green blade is beginning to cover with verdure the primeval soil. To Geology, the twin sister of Mineralogy, but of wider grasp by far and of loftier mind, Chemistry has for many years been offering her occasional aid. But the rough blockers-out of the young science were not prepared by their knowledge or pursuits to appreciate the nature and causes of by far the largest class of the manifold phenomena which the crust of our earth exhibits. The daring mind of Davy made the first bold application of chemical knowledge to the explanation of the most impressive physico-geological phenomena which the surface of the globe now exhibits. The metal potassium, one of his great discoveries, takes fire on contact with cold water, produces much heat, and liberates a large volume of elastic (hydrogen) gas. This property of his new metal carried the philosopher's mind at once to the burning volcano and the shattering earthquake. Give me,' he said, accumulations of potassium or sodium, or other analogous metals in the bowels of the earth, and let the waters of the sea descend to them, and all the phenomena of the volcano and of the earthquake may be produced.' There is no impossibility-scarcely an improbability, as he afterwards believed-that masses of these metals should here and there exist in the interior of the earth. And it was to him an interesting fact, that nearly all the active volcanoes then known were situated near the sea; from which, * The English Translation of this work was published in London -the first and second volumes in 1788, and the third in 1791., 1851. Later Chemical Geologists. 269 therefore, water might readily descend to such accumulations of his combustible metals. They are the cause of earthquakes 'and volcanoes,' was the conclusion, therefore, of his rapid and ardent mind; and thus he became the author and propounder of what was called the Chemical Theory of Volcanoes.' This theory, possessing both simplicity and beauty, was readily adopted by numerous philosophers. And, although the progress of knowledge has now greatly lessened the degree of special favour with which it used to be regarded even by inquirers after truth, yet many of Davy's old disciples still cling to it as the true doctrine of nature, and refuse materially to modify their early faith. Among English authors, this view is still upheld in the work of Dr. Daubeny*,- on other accounts a very valuable book; while a partial collection, especially of the physical facts, which are to aid future chemico-geologists in arriving at a general theory of both earthquakes and volcanoes, has been admirably commenced by Mr. Mallet of Dublin†, under the auspices, and in the published transactions, of the British Association for the Advancement of Science. But from every field or section of geological investigation, numerous chemical questions spring up. With igneous rocks, whether more ancient or more modern-with the so-called metamorphic or altered rocks, the origin, original nature and changes of each, and with the origin and relations of the numerous mineral substances they respectively contain-countless inquiries are connected which this science is called upon to answer. The slow changes to which deposits of gypsum, of rock-salt, of natron, and of nitrate of soda are due, demand for their elucidation profound chemical study. Coal and the combustible minerals, the mysterious amber and the precious diamond,their origin, the successive changes through which their first material passed before it assumed its final form, and what were the special circumstances by which these changes were induced, promoted, retarded, or arrested, -veins filled with metalliferous minerals, or with sparry contents of various kinds; stratified deposits and veins of phosphate of lime; mineral waters,—the nature, source, and constancy of their impregnations; pure water and steam, their agency under ordinary and extraordinary temperatures and pressures, in altering rocks and producing specific mineral combinations; the atmosphere, -its • Description of Active and Extinct Volcanoes. Second Edition, 8vo. London: 1848. First Report on the Facts of Earthquake Phenomena. By Robert Mallet, M.R. I. A. London: 1850. past and present constitution and history, its influence on the materials which form the earth's crust, and their influence again in modifying its composition; the changes which the remains of organised beings buried in the strata induce, or have themselves undergone during the prolonged action of natural causes, these make, severally, almost unlimited demands on the patience and sagacity of chemists, which the labours of many coming years will be unable fully to satisfy. Chemical geology will by and by be recognised as a department of geological science at least as distinct and valuable as the hitherto more popular and more generally interesting branch of Paleontology; and, as demanding a special knowledge in its cultivators at least equally extensive and profound. It will continue also to grow in interest and freshness long after the early zeal in behalf of mere descriptive geology and the geography of rocks has died. away. Since the time of Davy, numerous, though less ambitious, contributions to chemical geology have been made by Berzelius, Bonsdorff, Mitscherlich, Blum, Delesse, Deville, Ebelmen, and other chemical analysts and observers. Among the latter, Professor Bischoff of Bonn has of late years taken a prominent place. And he is at present rendering an important service to this branch of the science, by embodying, along with his own peculiar views and private experiments, a learned critique upon nearly all that has been done by others in a voluminous work,- Lehrbuch der Chemischen und Physicalischen Geologie,'-now issuing from the press, and of which the concluding part is promised during the present year. Lying between the two great divisions of mineral and organic chemistry, and belonging almost equally to both, are the interesting subjects of Allotropism, Isomerism, Polymerism, Catalysis, and some others, to which recent investigations have called the attention of philosophical chemists, and which tend daily to connect the familiar and sensible phenomena of the science with the most recondite considerations of molecular philosophy. But over these topics we most unwillingly pass, that we may devote a larger space to the already wide and rapidly growing department of organic chemistry. That this department should be large, will be admitted by the reader when he learns that it embraces the study of every part of every thing which lives or which has lived, and of countless compound bodies which are formed during the decay or artificial decomposition of the several parts of living things, animal or vegetable. Not only are the parts and products of 1851. Progress of Organic Chemistry. 271 each plant and animal very numerous, as well as the successive changes they undergo in the successive stages of their growth, and during various forms of disease, but each of the many thousands of living species in both kingdoms produces or contains some thing peculiar to itself, which chemistry must examine. Can any limit be assigned to a field so wide as this? During late years, the name of Liebig has been most prominently connected with the progress of organic chemistry. As, however, his career did not begin till the foundations of this line of inquiry had been' already laid, we must commence our sketch at an earlier period. The Alchemists had done little here. Their experimental trials were made for the most part upon mineral substances, although after the process of distillation came to be perfected, alcohol and some ethereal oils were discovered by them; succinic acid was obtained from amber; benzoic acid from gum benzoin; and vinegar and wood spirit from the dry distillation of wood. But it was not till towards the close of the phlogistic period that organic chemistry, in the hands of Bergman and Scheele, began to make any decided progress; nor till a still later period that it first received from Lavoisier a decidedly scientific character. Lavoisier applied to organic compounds the same method of interrogation by which he had effected his great reforms in inorganic chemistry. Of what elementary bodies does this organic compound consist?-of carbon, hydrogen, and oxygen, experiment answered. Then in what proportions by weight do they severally exist in it? Thus the use of the balance and the accuracy of numbers found their way also into this department of the science. Two things now became necessary to future progress,-to devise a set of methods by which organic compounds might be obtained in a pure state, possessing constant properties and composition; and a second set, by which their elementary constituents might be separated from each other, so completely and in such a form, as to admit of being respectively weighed and measured with the necessary degree of accuracy. The latter of these objects was only imperfectly attained by Lavoisier himself, and subsequently by Fourcroy, Vauquelin (1802) and de Saussure (1807). It was more completely arrived at through the processes introduced by Gay Lussac and Thenard (1810), and those recommended by Dr. Prout, and was virtually perfected through those employed by Berzelius in the analyses which he published in 1814. It is an important point in the history of analytical chemistry, to remark that, to the methods adopted in the year 1815, scarcely any thing has since been added by which greater accuracy can be secured. The introduction of Liebig's beautiful tube, and the successive valuable suggestions and processes of Dumas and others, have greatly simplified, and rendered more generally attainable, the rapid and facile performance of organic analyses; but they have added little to the accuracy of the results which a careful analyst could already arrive at by the methods of 1815. Of this truth we present the following illustration. Among the substances of which Berzelius had published analyses in 1814, were benzoic acid and benzoate of lead. It was our good fortune, subsequently, to be his guest in Stockholm in 1832, when he received from Liebig, by letter, an account of the most interesting researches of himself and Wöhler, into the nature of the oil of bitter almonds, and its kindred compounds. In this letter a doubt was expressed respecting the true formula for benzoic acid as deduced from the analyses published by Berzelius in 1814. We had, in consequence, the pleasure of witnessing a re-preparation, with his own hands, of the benzoate of lead, and a re-analysis of the acid it contained. The percentage results of these new trials were found, on turning back to the old note-book, to agree to the third place of decimals, with the numbers obtained for the composition of benzoic acid, twenty years before! The reader will not wonder that such a circumstance should have inspired us with great faith in the precision of the early as well as later methods and researches of this distinguished chemist. Among the successive steps of more or less importance, in the progress which this branch of the science began to make, after accurate methods of analysis had been discovered, that of Chevreul proved particularly effective. In his great work upon the fats, he showed the use of studying and analysing, not only the natural substances or compounds themselves, but the chemical changes also which they may undergo; and the new products and compounds they can be made to yield. And further, by comparing the composition as well of these products as of their combinations with other substances, with that of the natural bodies from which they were derived, he illustrated how one analysis might be made to control and test the accuracy of another; how, in this manner, most interesting views might be arrived at, in regard to the molecular constitution of organic compounds, and how, what had been hitherto very obscure chemical changes, might be lucidly explained. From him, * Recherches Chimiques sur les Corps gras d'Origine Animale. Par M. E. Chevreul. Paris: 1823. |