CHEMISTRY

And turtles; characterized by the body being inclosed between a double shield or shell, out of which extend the head, tail, and four extremities. The land tortoises have the power of retracting all these parts within the shell. CHEMISTRY. (The word is probably derived from the Coptic root chems or hhems, signifying obscure or secret. The German word geheim is apparently of the same origin.) Chemistry is a department of science, the objects of which are to investigate the nature and properties of the elements of matter, and their mutual actions and combinations; to ascertain tlie proportions in which they unite, and the modes of separating them when united; and to inquire into the laws and powers which preside over and affect these agencies. As an art, chemistry may be traced to a very remote period; but it can scarcely be said to have existed as a science previoui to the commencement of the seventeenth century: and in tracing its early history we shall find the principal materials upon which it is founded in the works of Bacon, Boyle, Hooke, Mayow, and Newton. As induction from experiment is the exclusive basis of chemical science, little progre could be made in it til' the futility of the ancient philosophical systems had been exposed,, and their influence annihilated, and till the nece ity of that form of severe experimental inquiry had been established which "first procures the light, and then shov/s the way by its means." Upon such foundations, laid by Bacon, the other philosophers whose names have been mentioned proceeded to bring together and arrange the materials which had been furnished by their predece ors, and were thence led into that train of true philosoi)hical reasoning and research which served as an emulatory example to their immediate succe ors, and which has led in our times to the gigantic results of modern discovery. It is well known that the alchemists had accumulated a number of valuable but isolated chemical facts, and that they had explored with considerable diligence the abstract properties and rauti»i agencies and relations of the greater number of natur?^^ products; but, with few exceptions, they neglected their useful and obvious applications, and wasted their labours upon unattainable and chimerical projects. Their discoveries and inventions, as Lord Bacon justly and forcibly observes, "are well represented in the fable of the old man who left an estate to his children, buried, as he said, in his vineyard, which therefore they fell to dig and search for with great diligence; whereby, though they found no gold in substance, yet they received an abundant vintage for their labour. So a uredly has the search and stir to make gold produced a great number of fruitful experiments." Alchemical speculations, including the attempts at the conversion of mercury into gold, and the search after antidotes and universal remedies, were vigorously carried on during the sixteenth and seventeenth centuries; and many amusing accounts of the profe ors and adepts of those periods have been handed down to us by the chemical historians of the time. Those who are curious upon these subjects may consult Man get us, Bibliotheca Chemic a, and the The at rum Chcmicum of Elias Ashmole: the latter contains " several poetic all pieces of our famous English philosophers, who have written the her met i que mysteries m their owne ancient language," but their perusal is labour lost; not so, however, with Basil Valentine, Para cels us, Van Helmont, and Glauber, in whose writings we not only find the materials so happily worked upon by Hooke and Mayow, but which also abound in announcements of important practical discoveries, and in hints to which many of the improvements of modern times may be plausibly traced. Basil Valentine of Erfurt was born about the year 1400; his writings, although tinctured with the follies of alchemy, are full of shrewd and inteUigent remarks: he was the discoverer, apparently, of nitric and of sulphuric acid, and of many antimonial preparations, which are fully described in his Triumphal Chariot. Philip Hochener, more commonly known under the name of Para cels us, and who died in 1541 at Saltzburgh, in the forty-third year of his age, is chiefly celebrated for the boldne and a iduity with which he introduced chemical preparations into the practice of medicine; he did little, however, as a discoverer. Van Helmont, one of the soundest writers of his period, was the first who seems to have paid attention to the nature of gaseous bodies, and to the distinction between permanent gases and vapours: the word gas first occurs in his works; and under the term gas silvestre, he seems to allude to what was afterwards tervaed fixed air. None, however, of these early practical chemists come into competition with Glauber. He was an active experimentalist, and an acute reason fir; and in reference to his discoveries we may enumerate among them the distillation of muriatic acid from a mixture of sulphuric acid and common salt; the purification of the residuary sulphate of soda, which he termed sal mirabile, and which still bears his name; the production of ammonia by the distillation of bone, and its conversion into 217 sal ammoniac by the addition of spirit of salt; the preparation of sulphate of ammonia, which he terms secret sal ammoniac; the formation of blue vitriol by the action of sulphuric acid upon the green rust of copper; the composition of numerous earthy, alkaline, and metallic salts; and lastly, the evolution of vinegar during the destructive distillation of wood, for which he describes and delineates the distillatory apparatus, under the name of "a pre for extracting the juice of wood," and the uses of which, together with those of the oil of tar and other products,he describes at length,closing his discourse with a statement of his apprehension that he shall be by many disbelieved; but " it contented me," he says, " that I have written the truth, and lighted a candle to my neighbours." Glauber also published a pamphlet, entitled " The Consolation of Navigators; in which is taught how they who travel by sea may preserve themselves from hunger and thirst, and also from those diseases which are wont to happen in long voyages: written for the health, comfort, and solace of all those who travel by water for the good of their country." The sensible plan of employing extract of malt as a portable vegetable diet, and diluted muriatic acid to quench thirst, is here recommended; and many of the medicinal uses of that acid are dwelt upon, among which are some that have been claimed as recent discoveries. On the whole, there is no author, contemporary with Glauber, who has written so much to the purpose, and who, as it were, anticipated so many of our modern scientific improvements. Reverting to the names of Boyle and his eminent a ociates, we are reminded of the origin of the Royal Society qf London for the Improvement of Natural Knowledge, which was incorporated by Charles II. in the year 1662, and of which Boyle and Hooke were active and distinguished members. Boyle died in 1G91. His station in life, his mild and prepo e ing disposition, his strict honour and integrity, and the unaffected earnestne with which he promoted experimental inquiry, tended to shed a lustre on his piysuits, to elevate their character with the world, and to draw into their precincts many who without such an example would have pa ed their lives in that listle inactivity then too common with those upon whom fortune smiled: among these Mr. Boyle made many converts. Boyle's E ays on the succe fulne and unsucce fulne of Experiments, and the Preface to his Philosophical Writings, are in the genuine spirit of experimental research; but the new and important aspect a umed about this time by such pursuits is perhaps chiefly due to Dr. Robert Hooke (born in the Isle of Wight in 1635, and died in London in 1702). Among his views and discoveries which bear upon the progre of chemical philosophy, the most important are those relating to the phenomena of combustion, and to the part which the air performs in that proce ; his notions upon these subjects are remarkable for their boldne as differing from the prevailing theories of the day, and for their correctne as superseding the objections to which those theories were liable. From the hints contained in the writings of the alchemists, it appears that the phenomena of combustion were referred to a subtile and highly volatile principle, which, agitated and expanded by heat, produced flame and fire. When metals were exposed to the action of heat the greater number of them were observed to alter their appearance, and, losing their brilliancy, became converted into an earth-like powder or calx. It was generally admitted that in this proce the particles of the combustible were thrown into violent vibrations, and in that way transformed into heat and light. But it had been also remarked that in certain cases of combustion, and especially as regards the metals, the phenomenon was attended by an actual increase of weight in the burning body, and that this result was incompatible with the theory which a umed the conversion of the combustible into heat and light, or the evolution of that principle of inflammability which by Beccher and Stahl and the chemists of that school was termed phlogi.it on. About the year 1630 a remarkable tract appeared in France relating to this subject, by Jean Rey, a physician of Perigord. Le Brun had pielted two pounds six ounces of lead, and found that in six hours the whole had been converted into calx; but that instead of having lost phlogiston, or any other ponderable matter, it had actually increased in weight to the extent of many ounces. Puzzled by this result, he consulted Rey as to its cause, who immediately undertook an experimental inquiry, which led him to refer the increase in weight in this and similar cases to the fixation of air. This inference was amply supported by the researches of Boyle and of Hooke: the former found that no combustible would burn under the exhausted receiver of the airpumj), and consequently that the presence of air was requisite; and Hooke, finding that however intensely charcoal was heated, it would not burn when air was excluded, infers " that air is the universal di olvent of inflammable bodies, and that this di olution generates heat, which we call^'jr." But he went a step beyond this, and Page 231