Earth (historical chemistry)

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Earths were historically defined by the Ancient Greeks as "materials that could not be changed further by the sources of heat then available". Several oxides were thought to be earths, such as aluminum oxide and magnesium oxide. It wasn't discovered until 1808 that these weren't elements but metallic oxides.


  • By 3000 BCE the Sumerians, perhaps while heating copper to make it more malleable, had discovered that more copper could be retrieved from the fire if the metal were heated with certain types of dirt and stones—that is, certain earths. These earths were the metal ores, and the process they discovered, smelting, reduced metal salts to pure metal by the action of carbon in the charcoal fire. The process of changing metal salts into pure metal is known as reduction because the metal without the accompanying oxygen, halogen, or sulfur of the salt weighs less than the ore. Eventually metal workers learned to distinguish various metal-bearing ores by color, texture, weight, flame color, or smell when heated (such as garlic odor of arsenic ores) and they could produce a desired material on demand.
    • Cathy Cobb, Harold Goldwhite, Creations of Fire: Chemistry's Lively History from Alchemy to the Atomic Age (1995) p. 8.
  • Pliny recorded processes involving metals, salts, sulfur, glass, mortar, soot, ash, and a large variety of chalks, earths, and stones. He describes the manufacture of charcoal; the enrichment of the soil with lime, ashes, and manure; the production of wines and vinegar; varieties of mineral waters; plants of medicinal or chemical interest; and types of marble, gems and precious stones. He discusses some simple chemical reactions... and a crude indicator paper... of papyrus strips soaked in an extract of oak galls that changed color when dipped in solutions of blue vitriol... contaminated with iron.
    • Cathy Cobb, Harold Goldwhite, Creations of Fire: Chemistry's Lively History from Alchemy to the Atomic Age (1995) p. 55.
  • The Earths are white, inodorous, tasteless, and uninflammable substances—non-conductors of electricity, insoluble in water, but soluble in one or more of the acids. Sp. gr. compared to that of water, not exceeding five to one. They are six in number; viz. silica, alumine, zircon, gluttine, augustine, ytria; the consideration of which falls under their alphabetical order.
  • What made silica so interesting was that... it did not seem to follow the established rules of chemical combination. In Smithson's time, chemical combination was... an acid combining with an alkali to produce a stable, neutral... "salt." Acids did not combine chemically with each other, nor did alkalis... [A] substance... found to contain an alkali... must also contain an acid—and vice versa. Bergman's description of the compounds containing earths as... "natural compositions of acids" meant... the other component must be alkaline—which the earths all seemed to be, except for silica.
    • Steven Turner, The Science of James Smithson: Discoveries from the Smithsonian Founder (2020) p. 96.

A Dictionary of Chemistry (1777)[edit]

Containing the Theory and Practice of that Science: Its Application to Natural Philosophy, Natural History, Medicine, and Animal Economy: With Full Explanations of the Qualities and Modes of Action of Chemical Remedies: And the Fundamental Principles of the Arts, Trades and Manufactures, Dependent on Chemistry. Translated from the French, with Notes, Additions, and Plates. The Second Edition. To which is Added, as an Appendix, A Treatise on the Various Kinds of Permanently, Elastic Fluids, or Gases. A translation of Dictionnaire de Chymie (1766) which is attributed to Pierre-Joseph Macquer. See Earths.
  • Earth is one of the four simple substances called elements, or primitive principles; because they are indeed the most simple of all those which enter into the combination of compound bodies. We cannot doubt, in particular, that the greatest part of the compounds which we can analyse contain earth as one of their principles; for after art has exhausted all its efforts to decompose them, a fixed and solid matter always remains, upon which no change can be produced; and this is what is generally called earth. It has the solidity, weight, fixity, and other principal properties of the mass of solid matter which forms the globe we inhabit, called also the earth.
  • These general considerations are sufficient to convince us, that in nature a substance exists whose properties are different from those of fire, air, water; and which is, like these other substances, one of the elements of compound bodies. But a vague assertion like this does not satisfy chemists. Besides the ascertaining of the exigence of the different substances submitted to their examination, they require to know the properties of these substances in their greatest degree of purity and simplicity; but they have found much difficulty and uncertainty in investigating the essential properties of the purest and simplest terrestrial element.
  • Earth is not found so pure as the other elements, fire, air, and water, which, though not entirely free from mixture, are however so pure, that we may certainly and easily discover their fundamental properties. These properties of each of these pure elements are so well ascertained, and so evident, that nobody has yet attempted to distinguish different kinds of fire, air, or water, notwithstanding the differences which may arise from the heterogeneous substances with which they are almost always mixed.
  • But we cannot say the same of earth; for a considerable number of substances are called earths, because they possess the principal properties of the terrestrial element: but these substances, when examined more particularly, are always found to differ from each other so much in other respects, and to be so difficultly purifiable from heterogeneous matter, that we have not ascertained whether only one simple and elementary earth, or several ones essentially different, although equally simple, exist.
  • The most general and most probable opinion is, that as only one kind of fire, of air, and of water, so only one kind of simple elementary earth, exists. Alchemists chiefly have endeavoured to discover this primary earth, not with an intention to ascertain its properties, but because they imagined that as gold is the purest of metals, the earth of which it is partly composed must be also the most pure; they have, therefore, searched every where for this earth, which they call pure earth and virgin earth. They have endeavoured to obtain it from dew, rain, the air, ashes of vegetables, animals, and several minerals: but it was impossible to find it in compound bodies; for we shall see that when once this element makes part of a compound body, it cannot be disengaged from the substances with which it has united.
  • Some of the best philosophical chemists have rather chose to admit different kinds of elementary earths, than to investigate the nature of the most simple and elementary of all. Becker admits three principles, which he calls earths, namely, the vitrifiable, the inflammable, and the mercurial earth...
  • Mr. Pott, examining the principal natural earths, divides them into four kinds, the vitrifiable, the calcareous, the argillaceous, and the gypseous earths. This able chemist shew the essential properties of these four kinds of earths, without affirming that they are all equally simple, and without even determining which of them he considered as most simple.
  • As earth is an element... it deserves an accurate investigation to discover which is the most simple and elementary of all the substances to which the name earth has been applied. ...considering, first, what are the essential properties by which earthy substances differ from other elements, and then by determining that earth to be the most pure and simple, which possesses these properties most eminently and decisively; for ...the more eminently any substance possesses these characteristic properties... the nearer it approaches to this element...
  • [A]ll the substances which may reasonably be considered as earthy... possess much greater weight, hardness, fixity, and infusibility, than any other element; for these qualities are insensible, or do dot exist, in the element of fire; they are in an exceedingly small degree in the air, and are more sensible and considerable in water; but are infinitely less than in any thing which can be considered as earth. Hence... the qualities above-mentioned are the distinguishing and characteristic essential properties of the earthy element. But these qualities are not so eminently united in any of those [earthy] substances... as in... vitrifiable earth. ...[T]hen ...this earth is the heaviest, hardest, most fixed, and most infusible, and even the most apyrous of all earths, when it is very pure; and also... the most homogeneous, the most simple, and elementary earth, as we shall prove by a more particular examination of its properties, and by a companion of these with the properties of the other earthy substances.
  • We call that vitrifiable earth, the integrant parts of which when united form masses of matter or stones, absolutely white and colorless, much more transparent and hard than any other natural substances, and which suffers no alteration, or even fusion, by the strongest fire which we can apply to it.
  • Amongst the hard stones called vitrifiable... few... strictly possess all the qualities... mentioned; because in very few... the vitrifiable earth is pure. Most of these stones, as hard pebbles of all kinds, sand, free-stone, agates, quartz, rock-crystal, and the stones called precious, are deficient in some... qualities required to constitute the purest vitrifiable earth. Some... are opake, or only semitransparent; others... colored; some... fusible by a great heat; and, lastly, others, although much harder than any other kind of stones, want the last degree of hardness; all which prove that they are mixed with heterogeneous substances, chiefly phlogistic, metallic, or even earthy, of a different kind.
  • The purest of all the vitrifiable stones is the diamond, which is perfectly white, free from all color or stain, and transparent. This stone is also known to be the hardest of all, is absolutely apyrous, that is, incapable of receiving any alteration by the most violent heat. We, therefore, consider the matter of this stone as the purest, simplest, and most elementary earth that is known. The properties, then, of this stone, and of the other vitrifiable stones which resemble it, may give us notions of the properties of primary, elementary, unchanged earth. In this our opinion is conformable to that of the illustrious Stahl, who indeed admits the three earths of Becker; but, at the same time, corrects the theory of this chemist, by declaring that he only considers the first earth of Becker, or vitrifiable earth, as the proper terrestrial or earthy element.
    • Note: Specimen Beckerianura, p. 44. No. 25.
  • [T]he name vitrifiable earth... may produce false notions of the nature of these stones.
  • [T]he epithet, vitrifiable is given, first, because some stones of this kind are, by means of their heterogeneous matters, capable of fusion and conversion into glass, without addition, and merely by the action of a very violent heat; and secondly, because other stones... require for their perfect fusion and vitrification a less quantity of flux, and a less degree of heat.
  • In the second place, as all the earths and stones called vitrifiable have, notwithstanding their impurity, more hardness and transparency than others, and are fitter to communicate these good qualities to glass, they are employed preferably to any other earths in the composition, of glass, or artificial crystal. These are the only reasons why this kind of earth has been called vitrifiable. But we ought not from thence to conclude, that the earthy substance [i.e., the earth element or principle] which almost entirely composes them is more fusible and more vitrifiable than other earths: on the contrary... vitrifiable earth, when very pure, is of all earths the least fusible, and the least vitrifiable.
  • I was present at a fine experiment made relatively to this subject. Some diamond powder was mixed with a sufficient quantity of fixed alkali to vitrify another earthy matter, and the mixture exposed to a heat sufficient for the most difficult vitrifications. After the operation, no glass was found in the crucible; but part of the alkali had been dissipated by the violence of the heat, and the diamond powder did not shew any signs of a beginning fusion. Thus we may confider it as an established truth, that the earths and stones called vitrifiable are not essentially and really so; that the fusibility of some of these, by which property they are rendered the fittest earths for vitrification, proceeds from heterogeneous matter with which they are mixed: and that, in general, the whitest, clearest, most transparent and hardest of these stones are also the most refractory and unfusible.
  • [T]he purest and simplest of all earths ought to be also the heaviest; and accordingly... pure vitrifiable earth is... heavier than calcareous, argillaceous, gypseous, or other earths. ...[N]evertheless ...metals, metallic earths, and several kinds of spars, both calcareous and selenitic, are much heavier than the most compact vitrifiable stones ... [P]arts may be so arranged that void spaces may be left betwixt them, sometimes larger, and sometimes less, therefore a body composed of parts essentially lighter, may yet have a greater specific gravity than another body whose parts are essentially heavier; and this happens in all metals and metallic matters. ...Thus the gravity of metals and of metallic earths and stones ought not to prevent our considering the pure and elementary earthy principle as the heaviest of all natural substances.
  • [W]e may consider the properties of elementary earth in the purest vitrifiable stones, and... compare them with the properties of the other elements. Since of these elements water is the most capable of our examination, we shall compare it with the purest vitrifiable earth; observing always, that we consider these elements in their state of aggregation; for we have no method by which their primary integrant parts can be known and considered separately.
  • I do not believe that a pure verifiable earth, as a diamond, can be fused even in the focus of the best burning speculums: but supposing that a sufficient heat might be produced... it would then melt, and would even be reduced to vapors, if the heat were sufficiently violent; and when this heat should cease, it would, when it cooled, fix again, and become such a substance as it was before. The same would happen to vitrifiable earth in these circumstances, which does happen to water rendered fluid, and reduced to vapor by a certain heat, and which is again frozen into solid ice when that heat is removed. The differences, therefore, betwixt these two substances are only... in the degrees; but also these differences are very considerable.
  • [A]n inference seems deducible, that the elements or the simplest substances which we know are essentially only one and the same matter, and only differ from each other in the quantity and in the form of their primary integrant molecules, which... have a greater or less tendency to unite together...
  • [W]e cannot doubt but that earth chiefly differs from the other elements by the powerful tendency which its parts have to each other, and by the force of their cohesion. For its hardness, fusibility, fixity, and even its gravity, are evidently the necessary consequences of this... the cause of the consistence of all solid bodies.
  • Lastly, as without fire the whole world would be one mass of solid and immoveable matter, so without earth it would be a confused heap of fogs, vapors, a chaos of incoherent atoms, destitute of that harmony and equilibrium which sustain it.
  • [T]he general tendency of the parts of matter to each other is the grand spring of the universe; that by this power, all combinations, solutions, and, in a word, all the movements and operations of nature are performed: and as... the earthy element possesses this tendency in the greatest degree, we ought to consider earth as being in this sense the most active and powerful of all elements. ...[T]he force with which they adhere together, and which renders them incapable of forming other unions, the extreme hardness, and the insolubility of a mass of pure earth, ought to demonstrate to a true philosopher, that if we suppose the parts of earth so separated ...that they cannot unite ...they must then possess all their force of tendency a state of violent effort, and consequently must tend with extreme force to unite with any parts of matter ...within their reach ...[W]e know compounds in which the primitive integrant parts of the earthy element are only combined with the parts of water, which are incapable of satisfying all their tendency to union. These are the most simple saline substances, such as acids and alkalis; and we may judge by the force and vehemence of the action of these solvents, how violent the action of the parts of earth would be, which should be capable of exerting all the attractive force which belongs to them.
  • Although the entire mass of our globe be probably formed by an immense heap of elementary, vitrifiable, and even actually vitrified earth, as the illustrious Buffon believes, we do not find upon its surface but a very small quantity of this earth, unaltered, and in its primary state. Perhaps even none of it exists in that state: for, as we have observed, the common vitrifiable stones, which are chiefly formed of it, are very far from the degree of purity of primary elementary earth; and even perfect diamonds, which seem of all these stones to approach the nearest to this purity, seem to have been elaborated by the waters, if we can judge from their regularly crystallized form.
  • We shall not be surprized at the scarcity of pure earthy element, if we consider that the surface of the earth... has been from the beginning of the world exposed to the constant action of the other elements; and that by uninterrupted operations, nature, assisted by fire, air, and water, has gradually disunited the integrant parts of elementary earth, and by combining them in manners and proportions infinitely various with parts of the other elements, has formed the numberless compound bodies, which occupy a certain thickness near the circumference of the globe, probably very small in comparison of the diameter of the earth, but very large with regard to us, whose greatest efforts only extend to a few hundred feet below its surface.
  • [T]he earth which makes [shells and scales] of the crustaceous animals... takes the character of that earth which is called calcareous, and which is capable of conversion into quicklime by the action of fire. The earth which has entered into the composition of plants, and even of the bodies of animals, after having been deprived... of... principles of these compounds to which it was united, forms all the argillaceous earths. Some... partake both of the calcareous and of the argillaceous properties, and are called marles. Marles have not yet been sufficiently well examined by chemists. They are either a mixture of clay and calcareous earth, or they have been so elaborated by nature as to be transformed into a particular earth, partly calcareous, and partly argillaceous, such as the earth of animal bones seems to be.
  • As the earth which forms sands and the common impure vitrifiable stones retains more than the rest the essential properties of elementary earth, notwithstanding the heterogeneous, phlogistic, and other parts with which it is mixed; we cannot easily know whether it has once made a part of some very compound bodies, from the principles of which it has been more perfectly separated than the argillaceous and calcareous earths; or whether it be the primitive earth, which, without having made part of any intimate combination, has only been divided and conveyed by waters, and the parts of which have afterwards reunited, having only contracted a slight union with some phlogistic, metallic, and other matters, with which it is found mixed. This latter supposition appears to me to be the most probable. But very extensive researches in natural history and in chemistry are requisite to determined this question.
  • [E]xcepting the purest vitrifiable earth, all the others are mixed with heterogeneous matter. By these remaining heterogeneous matters are the different kinds of earth specified and characterised: and as they all preserve and retain their peculiar character, we ought to conclude from thence, that these extraneous matters are very intimately united. To purify and simplify these mixed earths, so that they shall be assimilated to the purest vitrifiable earth, would be a fine problem. But, probably, this problem is beyond the power of our art. For... the perfect separation of two substances, united together, is exceedingly difficult, this difficulty must greatly increase, when one of the... substances... has a very strong attractive power, as earth has. This is the... reason why we find so small a portion of pure earth amongst the bodies within our reach; and that on the contrary, the globe is covered with so great a quantity of earthy substances differing from each other so much, that we might be inclined to believe them to be bodies essentially different.

Earth (Animal)[edit]

  • Earth (Animal) is the earth of shells of animals; or that which is obtained by calcination, or putrefaction of animal substances. 1. The earths of the shells of Sea Fishes have the general properties of calcareous earths. It is said to differ from the mineral calcareous earths in being more difficultly soluble by vitriolic acid, and in being less disposed to vitrify along with salts and metallic glasses. The shells of eggs are also calcareous, but are somewhat fusible by fire. 2. The earths of calcined bones and horns are soluble by nitrous, marine, and vegetable acids, and with difficulty by vitriolic acid; but are not capable of being converted into quicklime by calcination. They are said to be unfusible, even when mixed with salt, metallic glasses, and other fusible mixtures. They are therefore used in the composition of enamels and opake white glasses. Nevertheless, Wallerius affirms, that the earth of calcined bones, by intense heat, was changed, without addition, to a green glass. The same author says, that the earth of the whites and yolks of eggs was easily fusible, and that in general the fusibility of animal earths is in proportion to the softness of the parts from which they were obtained. 3. The earth of blood, flesh and skins of animals, is soluble by all acids, and is fusible by fire; that of blood and of other animal fluids being most fusible. This earth, like that of burnt bones and horns, is not calcareous; but both these kinds of earth are said to be rendered calcareous by being dissolved in acids, precipitated by fixed alkali from those acids, and afterwards calcined. They probably contain some mucilaginous substance, from which they cannot be entirely divested by fire without a previous solution in acids.

A Dictionary of Chemistry and Mineralogy, with Their Applications (1835)[edit]

by Andrew Ure, Fourth Edition, "Earths" pp. 408-409.
  • Twenty years ago few substances seemed more likely to retain a permanent place in chemical arrangements, than the solid and refractory earths which compose the crust of the globe.
  • Analysis has shewn, that the various stony or pulverulent masses which form our mountains, valleys, and plains, might be considered as resulting from combination or intermixture, in various numbers and proportions, of nine primitive earths, to which the following names were given:—
    1. Baryta. 2. Strontia. 3. Lime. 4. Magnesia. 5. Alumina, or clay. 6. Silica. 7. Glucina. 8. Zirconia. 9. Yttria.
  • The brilliant discovery by Sir H. Davy in 1808, of the metallic bases of potash, soda, strontia, and lime, subverted the ancient ideas regarding the earths, and taught us to regard them as all belonging, by most probable analogies, to the metallic class. According to an ingenious suggestion of Mr Smithson silica, however, ought to be ranked acids, since it has the power, in native mineral compounds, of neutralizing the alkaline earths, as well as the common metallic oxides. But as this property is also possessed by many metallic oxides, it can afford no evidence against the metallic nature of the siliceous basis. Alumina, by the experiments of Ehrman, may be made to saturate lime, producing a glass; and the triple compounds of magnesia, alumina, and lime, are perfectly neutral in porcelain. We might therefore refer alumina, as well as silica, to the same class with the oxides of antimony, arsenic, chromium, columbium, molybdenum, titanium, and tungsten. Alumina, however, bears to silica the same relation that oxide of antimony does to that of arsenic; the antecedent pair acting the part of bases, while the consequent pair act only as acids. The compound of the fluoric principle with silica is... mysterious... The almost universal function which silica enjoys, of saturating the alkaline oxides in the native earthy minerals, is exhibited in a very striking manner in Mr Allan's valuable Synoptic Tables. From his fifth to his fifteenth table of analyses, the column of silica is always complete, whatever deficiency or variation may occur in the columns of the earthy bases. At least, only a very few exceptions need be made for the oriental gems, which consist of strongly aggregated alumina.
  • Whatever may be the revolutions of chemical nomenclature, mankind will never cease to consider as Earths those solid bodies, composing the mineral strata, which are incombustible, colourless, not convertible into metals by all the ordinary methods of reduction, or, when reduced by scientific refinements, possessing but an evanescent metallic existence, and which either alone, or at least when combined with carbonic acid, are insipid and insoluble in water.

Heroes of Science. Chemists. (1883)[edit]

by M. M. Pattison Muir
  • Substances which resembled salts in general appearance, but were insoluble in water, and very fixed in the fire, were called "earths"; and, as was generally done in those days, the existence of a primordial earth was assumed, more or less of which was supposed to be present in actual earths. This recognition of the possibility of more or less of the primordial earth being present in actually occurring earths, of course necessitated the existence of various kinds of earth. The earths were gradually distinguished from each other; lime was recognized as a substance distinct from baryta, baryta as distinct from alumina, etc.
  • Stahl taught that one essential property of an earth was fusibility by fire, with production of a substance more or less like glass. This property was possessed in a remarkable degree by quartz or silica. Hence silica was regarded as the typical earth, until Berzelius, in 1815, proved it to be an acid. But the earths resembled alkalis, inasmuch as they too combined with, and so neutralized, acids.
  • There is an alkali hidden in every earth, said some chemists.
    An alkali is an earth refined by the presence of acid and combustible matter, said others.
3-fold division of Earths
  • Earths thus came to be included in the term "alkali," when that term was used in its widest acceptation. But a little later it was found that some of the earths were thrown down in the solid form from their solutions in acids by the addition of alkalis; this led to a threefold division... The distinction at first drawn between "earth" and "alkali" was too absolute; the intermediate group of "alkaline earths" served to bridge over the gap between the extreme groups.
  • At this stage of advance, then, an earth is regarded as differing from an alkali in being insoluble, or nearly insoluble in water; in not being soapy to the touch, and not turning vegetable reds to blue: but as resembling an alkali, in that it combines with and neutralizes an acid; and the product of this neutralization, whether accomplished by an alkali or by an earth, is called a salt.
  • To the earth or alkali, as being the foundation on which the salt is built, by the addition of acid, the name of base was given by Rouelle in 1744.
  • But running through every conception which was formed of these substances-acid, alkali, earth, salt-We find a tendency, sometimes forcibly marked, sometimes feebly indicated, but always present, to consider salt as a term of much wider acceptation... An acid and an alkali, or an acid and an earth, combine to form a salt; but the salt could not have been thus produced unless the acid, the alkali and the earth had contained in themselves some properties which, when combined, form the properties of the salt.
  • The acid, the alkali, the earth, each is, in a sense, a salt. The perfect salt is produced by the coalescence of the saltness of the acid with the saltness of the alkali. This conception finds full utterance in the names, once in common use, of sal acidum for acid, sal alkali for alkali, and sal salsum or sal neutrum for salt. All are salts; at one extreme comes that salt which is marked by properties called acid properties, at the other extreme comes the salt distinguished by alkaline properties, and between these, and formed by the union of these, comes the middle or neutral salt.
  • It is thus that the nomenclature of chemistry marks the advances made in the science. "What's in a name?" To the historical student of science, almost everything.

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