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Liebig's Chemical Letters


My dear Sir,

    The influence which the science of chemistryexercises upon human industry, agriculture, and commerce; upon physiology, medicine,and other sciences, is now so interesting a topic of conversation everywhere, thatit may be no unacceptable present to you if I trace in a few familiar letters someof the relations it bears to these various sciences, and exhibit for you its actualeffect upon the present social condition of mankind.

    In speaking of the present state of chemistry,its rise and progress, I shall need no apology if, as a preliminary step, I callyour attention to the implements which the chemist employs - the means which areindispensable to his labours and to his success.

    These consist, generally, of materials furnishedto us by nature, endowed with many most remarkable properties fitting them for ourpurposes; if one of them is a production of art, yet its adaptation to the use ofmankind, - the qualities which render it available to us, - must be referred to thesame source as those derived immediately from nature.

    Cork, Platinum, Glass, and Caoutchouc, are thesubstances to which I allude, and which minister so essentially to modern chemicalinvestigations. Without them, indeed, we might have made some progress, but it wouldhave been slow; we might have accomplished much, but it would have been far lessthan has been done with their aid. Some persons, by the employment of expensive substances,might have successfully pursued the science; but incalculably fewer minds would havebeen engaged in its advancement. These materials have only been duly appreciatedand fully adopted within a very recent period. In the time of Lavoisier, the richalone could make chemical researches; the necessary apparatus could only be procuredat a very great expense.

    And first, of Glass: every one is familiar withmost of the properties of this curious substance; its transparency, hardness, destitutionof colour, and stability under ordinary circumstances: to these obvious qualitieswe may add those which especially adapt it to the use of the chemist, namely, thatit is unaffected by most acids or other fluids contained within it. At certain temperaturesit becomes more ductile and plastic than wax, and may be made to assume in our hands,before the flame of a common lamp, the form of every vessel we need to contain ourmaterials, and of every apparatus required to pursue our experiments.

    Then, how admirable and valuable are the propertiesof Cork! How little do men reflect upon the inestimable worth of so common a substance!How few rightly esteem the importance of it to the progress of science, and the moraladvancement of mankind! - There is no production of nature or art equally adaptedto the purposes to which the chemist applies it. Cork consists of a soft, highlyelastic substance, as a basis, having diffused throughout a matter with propertiesresembling wax, tallow, and resin, yet dissimilar to all of these, and termed suberin.This renders it perfectly impermeable to fluids, and, in a great measure, even togases. It is thus the fittest material we possess for closing our bottles, and retainingtheir contents. By its means, and with the aid of Caoutchouc, we connect our vesselsand tubes of glass, and construct the most complicated apparatus. We form jointsand links of connexion, adapt large apertures to small, and thus dispense altogetherwith the aid of the brassfounder and the mechanist. Thus the implements of the chemistare cheaply and easily procured, immediately adapted to any purpose, and readilyrepaired or altered.

    Again, in investigating the composition of solidbodies, - of minerals, - we are under the necessity of bringing them into a liquidstate, either by solution or fusion. Now vessels of glass, of porcelain, and of allnon-metallic substances, are destroyed by the means we employ for that purpose, -are acted upon by many acids, by alkalies and the alkaline carbonates. Cruciblesof gold and silver would melt at high temperatures. But we have a combination ofall the qualities we can desire in Platinum. This metal was only first adapted tothese uses about fifty years since. It is cheaper than gold, harder and more durablethan silver, infusible at all temperatures of our furnaces, and is left intact byacids and alkaline carbonates. Platinum unites all the valuable properties of goldand of porcelain, resisting the action of heat, and of almost all chemical agents.

    As no mineral analysis could be made perfectlywithout platinum vessels, had we not possessed this metal, the composition of mineralswould have yet remained unknown; without cork and caoutchouc we should have requiredthe costly aid of the mechanician at every step. Even without the latter of theseadjuncts our instruments would have been far more costly and fragile. Possessingall these gifts of nature, we economise incalculably our time - to us more preciousthan money!

    Such are our instruments. An equal improvementhas been accomplished in our laboratory. This is no longer the damp, cold, fireproofvault of the metallurgist, nor the manufactory of the druggist, fitted up with stillsand retorts. On the contrary, a light, warm, comfortable room, where beautifullyconstructed lamps supply the place of furnaces, and the pure and odourless flameof gas, or of spirits of wine, supersedes coal and other fuel, and gives us all thefire we need; where health is not invaded, nor the free exercise of thought impeded:there we pursue our inquiries, and interrogate Nature to reveal her secrets.

    To these simple means must be added "TheBalance," and then we possess everything which is required for the most extensiveresearches.

    The great distinction between the manner ofproceeding in chemistry and natural philosophy is, that one weighs, the other measures.The natural philosopher has applied his measures to nature for many centuries, butonly for fifty years have we attempted to advance our philosophy by weighing.

    For all great discoveries chemists are indebtedto the "balance" - that incomparable instrument which gives permanenceto every observation, dispels all ambiguity, establishes truth, detects error, andguides us in the true path of inductive science.

    The balance, once adopted as a means of investigatingnature, put an end to the school of Aristotle in physics. The explanation of naturalphenomena by mere fanciful speculations, gave place to a true natural philosophy.Fire, air, earth, and water, could no longer be regarded as elements. Three of themcould henceforth be considered only as significative of the forms in which all matterexists. Everything with which we are conversant upon the surface of the earth issolid, liquid, or aeriform; but the notion of the elementary nature of air, earth,and water, so universally held, was now discovered to belong to the errors of thepast.

    Fire was found to be but the visible and otherwiseperceptible indication of changes proceeding within the, so called, elements.

    Lavoisier investigated the composition of theatmosphere and of water, and studied the many wonderful offices performed by an elementcommon to both in the scheme of nature, namely, oxygen: and he discovered many ofthe properties of this elementary gas.

    After his time, the principal problem of chemicalphilosophers was to determine the composition of the solid matters composing theearth. To the eighteen metals previously known were soon added twenty-four discoveredto be constituents of minerals. The great mass of the earth was shown to be composedof metals in combination with oxygen, to which they are united in one, two, or moredefinite and unalterable proportions, forming compounds which are termed metallicoxides, and these, again, combined with oxides of other bodies, essentially differentto metals, namely, carbon and silicium. If to these we add certain compounds of sulphurwith metals, in which the sulphur takes the place of oxygen, and forms sulphurets,and one other body, - common salt, - (which is a compound of sodium and chlorine),we have every substance which exists in a solid form upon our globe in any very considerablemass. Other compounds, innumerably various, are found only in small scattered quantities.

    The chemist, however, did not remain satisfiedwith the separation of minerals into their component elements, i.e. their analysis;but he sought by synthesis, i.e. by combining the separate elements and forming substancessimilar to those constructed by nature, to prove the accuracy of his processes andthe correctness of his conclusions. Thus he formed, for instance, pumice-stone, feldspar,mica, iron pyrites, &c. artificially.

    But of all the achievements of inorganic chemistry,the artificial formation of lapis lazuli was the most brilliant and the most conclusive.This mineral, as presented to us by nature, is calculated powerfully to arrest ourattention by its beautiful azure-blue colour, its remaining unchanged by exposureto air or to fire, and furnishing us with a most valuable pigment, Ultramarine, moreprecious than gold!

    The analysis of lapis lazuli represented itto be composed of silica, alumina, and soda, three colourless bodies, with sulphurand a trace of iron. Nothing could be discovered in it of the nature of a pigment,nothing to which its blue colour could be referred, the cause of which was searchedfor in vain. It might therefore have been supposed that the analyst was here altogetherat fault, and that at any rate its artificial production must be impossible. Nevertheless,this has been accomplished, and simply by combining in the proper proportions, asdetermined by analysis, silica, alumina, soda, iron, and sulphur. Thousands of poundsweight are now manufactured from these ingredients, and this artificial ultramarineis as beautiful as the natural, while for the price of a single ounce of the latterwe may obtain many pounds of the former.

    With the production of artificial lapis lazuli,the formation of mineral bodies by synthesis ceased to be a scientific problem tothe chemist; he has no longer sufficient interest in it to pursue the subject. Hemay now be satisfied that analysis will reveal to him the true constitution of minerals.But to the mineralogist and geologist it is still in a great measure an unexploredfield, offering inquiries of the highest interest and importance to their pursuits.

    After becoming acquainted with the constituentelements of all the substances within our reach and the mutual relations of theseelements, the remarkable transmutations to which the bodies are subject under theinfluence of the vital powers of plants and animals, became the principal objectof chemical investigations, and the highest point of interest. A new science, inexhaustibleas life itself, is here presented us, standing upon the sound and solid foundationof a well established inorganic chemistry. Thus the progress of science is, likethe development of nature's works, gradual and expansive. After the buds and branchesspring forth the leaves and blossoms, after the blossoms the fruit.

    Chemistry, in its application to animals andvegetables. endeavours jointly with physiology to enlighten us respecting the mysteriousprocesses and sources of organic life.