Factitious airs is an archaic term for synthetic gases coined by Robert Boyle around 1670 .
Factitious airs (also factitious air or artificial airs) was a term used in 17th- to early 19th-century pneumatic chemistry for any gas, then called an "elastic fluid", that could be artificially produced from solid or liquid bodies by chemical reaction, fermentation, putrefaction, distillation, dissolution, or heat. The phrase was coined by Robert Boyle around 1670 while isolating what is now recognized as hydrogen (which he termed "inflammable air").
The term was rigorously defined by Henry Cavendish in his landmark 1766 paper Three papers, containing experiments on factitious air. Cavendish described factitious air as "any kind of air which is contained in other bodies in an unelastic state, and is produced from thence by art". At the time, these gases were understood to be distinct from ordinary atmospheric air and were rarely obtained in pure form; archaic nomenclature was therefore inconsistent and often applied overlapping or mistaken labels to the same substance.
The study of factitious airs encompassed what are now known as hydrogen ("inflammable air"), carbon dioxide ("fixed air" or "fixible air"), ammonia ("alkaline air" or "volatile alkali"), oxygen ("dephlogisticated air", "vital air", or "oxygene"), nitrous oxide ("dephlogisticated nitrous air"), nitric oxide ("nitrous air"), carbon monoxide ("hydrocarbonate" or "water gas"), methane ("marsh gas" or "carburetted hydrogen"), hydrogen sulfide ("hepatic air"), and several others. These investigations were central to the development of pneumatic chemistry, the refinement and eventual overthrow of phlogiston theory, and the Chemical Revolution led by Antoine Lavoisier. The same body of work also laid the foundation for pneumatic medicine, most notably through the efforts of Thomas Beddoes and James Watt at the Pneumatic Institution in the 1790s, where factitious airs were trialed as treatments for tuberculosis and other conditions.
With the widespread acceptance of LavoisierâÂÂs oxygen theory and the new chemical nomenclature in the late 1780s and 1790s, the archaic term "factitious airs" gradually fell out of use.
Factitious means "artificial, not natural", so the term means "man-made gases".
An archaic definition from 1747 for the production of factitious air was defined as being caused by: "1- by flow Degrees from Putrefactions and Fermentations of all Kinds; or 2- more expeditiously by some Sorts of chymical Dissolutions of Bodies; or 3- and lastly, almost instantaneously by the Explosion of Gunpowder, and the Mixture or some Kinds of Bodies. Thus, if Paste or Dough with Leaven be placed in an exhausted Receiver, it will, after some Time, by Fermentation, produce a considerable quantity of Air, which will appear very plainly by the Sinking the Quicksilver in the Gage. Thus also any Animal or Vegetable Substance, putrifying in Vacuo, will produce the same Effect."
There are significant inconsistencies in the ancient nomenclature due to the limited knowledge of chemistry and primitive analytical technology of the era (i.e. based on the chemistry, it is clear the terms were mistakenly assigned to more than one gas by different investigators). Furthermore, in most cases the gases were not pure.Historical names used for factitious airs may have included:
Gaseous ammonia was first isolated by Joseph Black in 1756 by reacting sal ammoniac (ammonium chloride) with calcined magnesia (magnesium oxide). It was isolated again by Peter Woulfe in 1767, by Carl Wilhelm Scheele in 1770 . In 1785, Claude Louis Berthollet ascertained its composition.
Fixed air, or fixible air, is an ancient term for carbon dioxide
Joseph Priestley credited Joseph Black for discovering and coining "fixed air", which was thought to exist in a fixed state in alkaline salts, chalk, and other calcareous substances. Black considered substances containing fixed air to be "mild", and upon expulsion of the gas by heating the resulting state is "caustic" by corroding or burning plants and animals (e.g. released by chalk upon decomposition to calcium oxide). In other words, the fixed air (also known as fixible air) was thought to be fixated within a corrosive molecule.
Priestley likewise credited the discovery of fixed air to contributions from several scientists including: David Macbride, John Pringle, William Brownrigg (regarded carbonated water to have an acidulous taste), Stephen Hales, and many others.
Henry Cavendish provided a definition: "By fixed air, I mean that particular species of factitious air, which is separated from alkaline substances by solution in acids or by calcination". Cavendish essentially defined potassium oxide or calcium oxide as a base, which can contain a fixated air within its composition, setting the stage for the historical definition of carbonate.
According to Claude Louis Berthollet, "What has long been called fixed, or fixible air, being really an acid in the state of gas, has of late received several new denominations. It has been called aerial acid, as existing very readily in the state of air, or more properly of gas, and plentifully in the atmosphere. The chalky acid, as procurable in large quantities from chalk, or other mild calcareous substances. The name given to it in this essay is derived from the knowledge of its composition, as lately ascertained by the French Chemists to consist of the elementary part of charcoal, named charbone, or char, united with oxygen, or the acidifying principle. Hence it is called, with strict propriety, carbonic acid in general; carbonic acid gas when in the aerial form; and carbonic acid liquor when combined with or dissolved in water."
By French Chemists, Berthollet is generally referring to Lavoisier's oxidation discoveries. The name oxygen is derived from Greek with oxy meaning acid, and gene to mean forming/expression, therefore carbonic acid is simply the union of carbon with oxygen (Laviosier's original degrees of oxidation could not fit the concept of carbon monoxide as it was based on diamond, graphite, coal and carbonic acid)
The 1804 definition by John Sadler of the Pneumatic Institution is, "A peculiar elastic fluid possessed of acid properties, formerly called fixed air, produced when charcoal or diamond is burned in oxygene; its is carbon perfectly oxygenated. It contains carbon 1, oxygene 4.
Carbonate was defined as "a compound formed by the union of carbonic acid with an earth, alkali, or metallic oxide [...] they are distinguished by the property of effervescing on the addition of an acid" The definition expands upon fixed air being fixated within carbonate to suggest carbonic acid is a constituent of carbonate, therefore in the ancient language the suffix "-ic acid" and "-ate" were not interchangeable.
The modern definition is similar, although equipped with the molecular knowledge of carbonate's structure and reassignment of the meaning of carbonic acid from CO<sub>2</sub> to the H<sub>2</sub>CO<sub>3</sub> molecule, "Carbonates are the salts of carbonic acids. They form when a positively charged metal ion comes into contact with the oxygen atoms of the carbonate ion."
Bicarbonate, originally known as bi-carbonate of potash, was coined by William Hyde Wollaston in 1814 based on hydrocarbonate's potential to release two molar equivalents of carbon dioxide (referred to as carbonic acid at the time) as released by both potassium hydrocarbonate (initially known as carbonate of potash, suggested to become bicarbonate) and potassium carbonate (vaguely known as subcarbonate, suggested to become carbonate) upon formation of potash (potassium oxide).
Bicarbonates have historically been defined as, "combinations of the bases with the carbonic acid, in which two atoms of the latter are united to one of the former" In other words, potash (potassium oxide) was well-understood to be a caustic base and essentially the core molecule that subsequent chemical nomenclature was built upon. Carbonate of potash (potassium carbonate) must contain a carbonic acid species fixated within potash's alternative composition (see fixed air above). Since "bi-carbonate of potash" liberates a double dose of carbonic acid, to distinguish between the similar substances, the prefix bi- indicates the bi-carbonate of potash (potassium hydrocarbonate) contains twice as much fixated in this form potash's composition relative to the carbonate of potash. The same ancient logic (prior to the understanding of molecular formulas and reaction stoichiometry) applied to soda, carbonate of soda, and bicarbonate of soda.
The word saleratus, from Latin sal æratus (meaning "aerated salt"), was widely used beginning in the 1840s.
Carbonic acid gas was an ancient term to specify the gaseous state of carbonic acid (synonymous with carbonic acid). It is listed as an alternative name for carbon dioxide in PubChem. In 1796 externally applied carbonic acid gas to the epidermis was reported to treat breast cancer; and inhalation treated tuberculosis and other indications. Henry Hill Hickman evaluated carbonic acid gas (produced by mixing sulfuric acid with carbonate of lime) for a surgical anesthetic.
Hydrogen was initially thought to be toxic based on experiments by Lavoisier, however, the purity of the hydrogen was taken into question when later experiments discovered hydrogen to effectively treat measles in the 1790s.
Blood has been understood to absorb and deliver oxygen since the mid-1790s.
The study of these airs interfaced with phlogiston theory.
The therapeutic potential of factitious airs were widely investigated with significant contributions by Thomas Beddoes, James Watt, James Lind, Humphry Davy, Robert John Thornton, and others at the Pneumatic Institution. Georgiana Cavendish, Duchess of Devonshire (related to Henry through marriage) had a profound interest in chemistry with interest in Henry's research in pneumatic chemistry. She played a pivotal role in advancing the study of factitious airs through partnering with Thomas Beddoes to establish the Pneumatic Institution.
Tuberculosis was a primary disease physicians had attempted to treat with factitious airs, particularly since James Watt's daughter died of the disease. John Carmichael had reported successfully treating a patient suffering from tuberculosis using hydrocarbonate. This application of factitious air was pioneering research relevant to the modern era as carbon monoxide currently has preclinical evidence of treating Mycobacterium tuberculosis infection progression by inducing dormancy, stimulating host immune response, and ameliorating host inflammation.