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In the history of science, pneumatic chemistry is an area of scientific research of the seventeenth, eighteenth, and early nineteenth centuries. Important goals of this work were the understanding of the physical properties of
gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
es and how they relate to
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breakin ...
s and, ultimately, the composition of
matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic parti ...
. The rise of
phlogiston theory The phlogiston theory is a superseded scientific theory that postulated the existence of a fire-like element called phlogiston () contained within combustible bodies and released during combustion. The name comes from the Ancient Greek (''bur ...
, and its replacement by a new theory after the discovery of oxygen as a gaseous component of the
Earth atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
and a
chemical reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...
participating in the
combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...
reactions, were addressed in the era of pneumatic chemistry.


Air as a reagent

In the eighteenth century, as the field of chemistry was evolving from
alchemy Alchemy (from Arabic: ''al-kīmiyā''; from Ancient Greek: χυμεία, ''khumeía'') is an ancient branch of natural philosophy, a philosophical and protoscientific tradition that was historically practiced in China, India, the Muslim worl ...
, a field of the natural philosophy was created around the idea of air as a reagent. Before this, air was primarily considered a static substance that would not react and simply existed. However, as
Lavoisier Antoine-Laurent de Lavoisier ( , ; ; 26 August 17438 May 1794),
CNRS (
Stephen Hales Stephen Hales (17 September 16774 January 1761) was an English clergyman who made major contributions to a range of scientific fields including botany, pneumatic chemistry and physiology. He was the first person to measure blood pressure. He al ...
. These reactions would give off different "airs" as chemists would call them, and these different airs contained more simple substances. Until Lavoisier, these airs were considered separate entities with different properties; Lavoisier was responsible largely for changing the idea of air as being constituted by these different airs that his contemporaries and earlier chemists had discovered. This study of gases was brought about by Hales with the invention of the pneumatic trough, an instrument capable of collecting the gas given off by reactions with reproducible results. The term ''gas'' was coined by J. B. van Helmont, in the early seventeenth century. This term was derived from the Ancient Greek word ''χάος,
chaos Chaos or CHAOS may refer to: Arts, entertainment and media Fictional elements * Chaos (''Kinnikuman'') * Chaos (''Sailor Moon'') * Chaos (''Sesame Park'') * Chaos (''Warhammer'') * Chaos, in ''Fabula Nova Crystallis Final Fantasy'' * Cha ...
'', as a result of his inability to collect properly the substances given off by reactions, as he was the first natural philosopher to make an attempt at carefully studying the third type of matter. However, it was not until Lavoisier performed his research in the eighteenth century that the word was used universally by scientists as a replacement for ''airs''. Van Helmont (1579 – 1644) is sometimes considered the founder of pneumatic chemistry, as he was the first natural philosopher to take an interest in air as a reagent.
Alessandro Volta Alessandro Giuseppe Antonio Anastasio Volta (, ; 18 February 1745 – 5 March 1827) was an Italian physicist, chemist and lay Catholic who was a pioneer of electricity and power who is credited as the inventor of the electric battery and the ...
began investigating pneumatic chemistry in 1776 and argued that there were different types of inflammable air based on experiments on marsh gases. Pneumatic chemists credited with discovering chemical elements include
Joseph Priestley Joseph Priestley (; 24 March 1733 – 6 February 1804) was an English chemist, natural philosopher, separatist theologian, grammarian, multi-subject educator, and liberal political theorist. He published over 150 works, and conducted exp ...
, Henry Cavendish,
Joseph Black Joseph Black (16 April 1728 – 6 December 1799) was a Scottish physicist and chemist, known for his discoveries of magnesium, latent heat, specific heat, and carbon dioxide. He was Professor of Anatomy and Chemistry at the University of Glas ...
,
Daniel Rutherford Daniel Rutherford (3 November 1749 – 15 December 1819) was a Scottish physician, chemist and botanist who is known for the isolation of nitrogen in 1772. Life Rutherford was born on 3 November 1749, the son of Anne Mackay and Professor John ...
, and
Carl Scheele Carl Wilhelm Scheele (, ; 9 December 1742 – 21 May 1786) was a Swedish German pharmaceutical chemist. Scheele discovered oxygen (although Joseph Priestley published his findings first), and identified molybdenum, tungsten, barium, hyd ...
. Other individuals who investigated gases during this period include Robert Boyle,
Stephen Hales Stephen Hales (17 September 16774 January 1761) was an English clergyman who made major contributions to a range of scientific fields including botany, pneumatic chemistry and physiology. He was the first person to measure blood pressure. He al ...
,
William Brownrigg William Brownrigg ( – 6 January 1800) was a British doctor and scientist, who practised at Whitehaven in Cumberland. While there, Brownrigg carried out experiments that earned him the Copley Medal in 1766 for his work on carbonic acid gas. He ...
,
Antoine Lavoisier Antoine-Laurent de Lavoisier ( , ; ; 26 August 17438 May 1794),
CNRS (
Joseph Louis Gay-Lussac Joseph Louis Gay-Lussac (, , ; 6 December 1778 – 9 May 1850) was a French chemist and physicist. He is known mostly for his discovery that water is made of two parts hydrogen and one part oxygen (with Alexander von Humboldt), for two laws ...
, and
John Dalton John Dalton (; 5 or 6 September 1766 – 27 July 1844) was an English chemist, physicist and meteorologist. He is best known for introducing the atomic theory into chemistry, and for his research into colour blindness, which he had. Colour b ...
.


History


Chemical revolution

"In the years between 1770 and 1785, chemists all over Europe started catching, isolating, and weighing different gasses." The
pneumatic trough A pneumatic trough is a piece of laboratory apparatus used for collecting gases, such as hydrogen, oxygen and nitrogen.It is mainly made of glass or various fibres and are of various sizes.It was invented by Stephen Hales. Description Four it ...
was integral to the work with gases (or, as contemporary chemists called them, airs). Work done by Joseph Black, Joseph Priestley, Herman Boerhaave, and Henry Cavendish revolved largely around the use of the instrument, allowing them to collect airs given off by different chemical reactions and combustion analyses. Their work led to the discovery of many types of airs, such as dephlogisticated air (discovered by Joseph Priestley). Moreover, the chemistry of airs was not limited to combustion analyses. During the eighteenth century, many chymists used the discovery of airs as a new path for exploring old problems, with one example being the field of medicinal chemistry. One particular Englishman, James Watt, began to take the idea of airs and use them in what was referred to as ''pneumatic therapy'', or the use of airs to make laboratories more workable with fresh airs and also aid patients with different illnesses, with varying degrees of success. Most human experimentation done was performed on the chymists themselves, as they believed that self-experimentation was a necessary part or progressing the field.


Contributors


James Watt

James Watt James Watt (; 30 January 1736 (19 January 1736 OS) – 25 August 1819) was a Scottish inventor, mechanical engineer, and chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1776, which was fu ...
's research in pneumatic chemistry involved the use of inflammable ( H2) and dephlogisticated ( O2) airs to create water. In 1783, James Watt showed that water was composed of inflammable and dephlogisticated airs, and that the masses of gases before combustion were exactly equal to the mass of water after combustion. Until this point, water was viewed as a fundamental element rather than a compound. James Watt also sought to explore the use of different "
factitious airs Factitious airs was a term used for synthetic gases which emerged around 1670 when Robert Boyle coined the term upon isolating what is now understood to be hydrogen. ''Factitious'' means "artificial, not natural", so the term means "man-made gases ...
" such as hydrocarbonate in medicinal treatments as "pneumatic therapy" by collaborating with Dr.
Thomas Beddoes Thomas Beddoes (13 April 176024 December 1808) was an English physician and scientific writer. He was born in Shifnal, Shropshire and died in Bristol fifteen years after opening his medical practice there. He was a reforming practitioner and t ...
and
Erasmus Darwin Erasmus Robert Darwin (12 December 173118 April 1802) was an English physician. One of the key thinkers of the Midlands Enlightenment, he was also a natural philosopher, physiologist, slave-trade abolitionist, inventor, and poet. His poems ...
to treat Jessie Watt, his daughter suffering from tuberculosis, using fixed air.


Joseph Black

Joseph Black Joseph Black (16 April 1728 – 6 December 1799) was a Scottish physicist and chemist, known for his discoveries of magnesium, latent heat, specific heat, and carbon dioxide. He was Professor of Anatomy and Chemistry at the University of Glas ...
was a chemist who took interest in the pneumatic field after studying under
William Cullen William Cullen FRS FRSE FRCPE FPSG (; 15 April 17105 February 1790) was a Scottish physician, chemist and agriculturalist, and professor at the Edinburgh Medical School. Cullen was a central figure in the Scottish Enlightenment: He was ...
. He was first interested in the topic of magnesia alba, or magnesium carbonate (MgCO3), and limestone, or calcium carbonate (CaCO3), and wrote a dissertation called "''De humore acido a cibis orto, et magnesia alba''" on the properties of both. His experiments on magnesium carbonate led him to discover that fixed air, or carbon dioxide (CO2), was being given off during reactions with various chemicals, including
breathing Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen. All aerobic creatures need oxygen for cellula ...
. Despite him never using the pneumatic trough or other instrumentation invented to collect and analyze the airs, his inferences led to more research into fixed air instead of common air, with the trough actually being used. Gaseous
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
was first isolated by
Joseph Black Joseph Black (16 April 1728 – 6 December 1799) was a Scottish physicist and chemist, known for his discoveries of magnesium, latent heat, specific heat, and carbon dioxide. He was Professor of Anatomy and Chemistry at the University of Glas ...
in 1756 by reacting ''sal ammoniac'' ( ammonium chloride) with ''calcined magnesia'' (
magnesium oxide Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions ...
). It was isolated again by
Peter Woulfe Peter Woulfe (1727–1803) was an Anglo-Irish chemist and mineralogist. He first had the idea that wolframite might contain a previously undiscovered element (tungsten). In 1771, Woulfe reported the formation of a yellow dye when indigo was tre ...
in 1767, by
Carl Wilhelm Scheele Carl Wilhelm Scheele (, ; 9 December 1742 – 21 May 1786) was a Swedish German pharmaceutical chemist. Scheele discovered oxygen (although Joseph Priestley published his findings first), and identified molybdenum, tungsten, barium, hydroge ...
in 1770


Joseph Priestley

Joseph Priestley Joseph Priestley (; 24 March 1733 – 6 February 1804) was an English chemist, natural philosopher, separatist theologian, grammarian, multi-subject educator, and liberal political theorist. He published over 150 works, and conducted exp ...
, in ''Observations on different kinds of air,'' was one of the first people to describe air as being composed of different states of matter, and not as one element. Priestley elaborated on the notions of fixed air (CO2),
mephitic air Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh ...
and inflammable air to include "inflammable nitrous air," " vitriolic acid air," "
alkaline air Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wast ...
" and " dephlogisticated air". Priestley also described the process of respiration in terms of
phlogiston theory The phlogiston theory is a superseded scientific theory that postulated the existence of a fire-like element called phlogiston () contained within combustible bodies and released during combustion. The name comes from the Ancient Greek (''bur ...
. Priestley also established a process for treating scurvy and other ailments using fixed air in his ''Directions for impregnating water with fixed air.'' Priestley's work on pneumatic chemistry had an influence on his natural world views. His belief in an "aerial economy" stemmed from his belief in "dephlogisticated air" being the purest type of air and that phlogiston and combustion were at the heart of nature. Joseph Priestley chiefly researched with the pneumatic trough, but he was responsible for collecting several new
water-soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...
airs. This was achieved primarily by his substitution of mercury for water, and implementing a shelf under the head for increased stability, capitalizing on the idea Cavendish proposed and popularizing the mercury pneumatic trough.


Herman Boerhaave

While not credited for direct research into the field of pneumatic chemistry,
Boerhaave Herman Boerhaave (, 31 December 1668 – 23 September 1738Underwood, E. Ashworth. "Boerhaave After Three Hundred Years." ''The British Medical Journal'' 4, no. 5634 (1968): 820–25. https://www.jstor.org/stable/20395297.) was a Dutch botanist, ...
(teacher, researcher, and scholar) did publish the ''Elementa Chimiae'' in 1727. This treatise included support for Hales' work and also elaborated upon the idea of airs. Despite not publishing his own research, this section on airs in the ''Elementa Chimiae'' was cited by many other contemporaries and contained much of the current knowledge of the properties of airs. Boerhaave is also credited with adding to the world of chemical thermometry through his work with Daniel Fahrenheit, also discussed in ''Elementa Chimiae.''


Henry Cavendish

Henry Cavendish, despite not being the first to replace water in the trough with mercury, was among the first to observe that fixed air was insoluble over mercury and therefore could be collected more efficiently using the adapted instrument. He also characterized fixed air ( CO2) and inflammable air ( H2). Inflammable air was one of the first gases isolated and discovered using the pneumatic trough. However, he did not exploit his own idea to its limit, and therefore did not use the mercury pneumatic trough to its full extent. Cavendish is credited with nearly correctly analyzing the content of gases in the atmosphere. Cavendish also showed that inflammable air and
atmospheric air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...
could be combined and heated to produce water in 1784.


Stephen Hales

In the eighteenth century, with the rise of combustion analysis in chemistry,
Stephen Hales Stephen Hales (17 September 16774 January 1761) was an English clergyman who made major contributions to a range of scientific fields including botany, pneumatic chemistry and physiology. He was the first person to measure blood pressure. He al ...
invented the pneumatic trough in order to collect gases from the samples of matter he used; while uninterested in the properties of the gases he collected, he wanted to explore how much gas was given off from the materials he burned or let
ferment Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
. Hales was successful in preventing the air from losing its "elasticity," i.e. preventing it from experiencing a loss in volume, by bubbling the gas through water, and therefore dissolving the soluble gases. After the invention of the pneumatic trough, Stephen Hales continued his research into the different airs, and performed many Newtonian analyses of the various properties of them. He published his book ''Vegetable Staticks'' in 1727, which had a profound impact on the field of pneumatic chemistry, as many researchers cited this in their academic papers. In ''Vegetable Staticks'', Hales not only introduced his trough, but also published the results he obtained from the collected air, such as the elasticity and composition of airs along with their ability to mix with others.


Instrumentation


Pneumatic trough

Stephen Hales Stephen Hales (17 September 16774 January 1761) was an English clergyman who made major contributions to a range of scientific fields including botany, pneumatic chemistry and physiology. He was the first person to measure blood pressure. He al ...
, called the creator of pneumatic chemistry, created the
pneumatic trough A pneumatic trough is a piece of laboratory apparatus used for collecting gases, such as hydrogen, oxygen and nitrogen.It is mainly made of glass or various fibres and are of various sizes.It was invented by Stephen Hales. Description Four it ...
in 1727. This instrument was widely used by many chemists to explore the properties of different airs, such as what was called inflammable air (what is modernly called hydrogen). Lavoisier used this in addition to his gasometer to collect gases and analyze them, aiding him in creating his list of simple substances. The pneumatic trough, while integral throughout the eighteenth century, was modified several times to collect gases more efficiently or just to collect more gas. For example, Cavendish noted that the amount of fixed air that was given off by a reaction was not entirely present above the water; this meant that fixed water was absorbing some of this air, and could not be used quantitatively to collect that particular air. So, he replaced the water in the trough with mercury instead, in which most airs were not soluble. By doing so, he could not only collect all airs given off by a reaction, but he could also determine the solubility of airs in water, beginning a new area of research for pneumatic chemists. While this was the major adaptation of the trough in the eighteenth century, several minor changes were made before and after this substitution of mercury for water, such as adding a shelf to rest the head on while gas collection occurred. This shelf would also allow for less conventional heads to be used, such as Brownrigg's animal
bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine en ...
. A practical application of a pneumatic trough was the
eudiometer A eudiometer is a laboratory device that measures the change in volume of a gas mixture following a physical or chemical change. Description Depending on the reaction being measured, the device can take a variety of forms. In general, it is ...
, which was used by
Jan Ingenhousz Jan (or John) Ingenhousz or Ingen-Housz FRS (8 December 1730 – 7 September 1799) was a Dutch-born British physiologist, biologist and chemist. He is best known for discovering photosynthesis by showing that light is essential to the process ...
to show that plants produced dephlogisticated air when exposed to sunlight, a process now called photosynthesis.Geerdt Magiels (2009) ''From Sunlight to Insight. Jan IngenHousz, the discovery of photosynthesis & science in the light of ecology'', Chapter 5: A crucial instrument: the rise and fall of the eudiometer, pages=199-231, VUB Press


Gasometer

During his chemical revolution, Lavoisier created a new instrument for precisely measuring out gases. He called this instrument the '' gazomètre''. He had two different versions; the one he used in demonstrations to the
Académie An academy (Attic Greek: Ἀκαδήμεια; Koine Greek Ἀκαδημία) is an institution of secondary or tertiary higher learning (and generally also research or honorary membership). The name traces back to Plato's school of philosophy, f ...
and to the public, which was a large expensive version meant to make people believe that it had a large precision, and the smaller, more lab practical, version with a similar precision. This more practical version was cheaper to construct, allowing more chemists to use Lavoisier's instrument.


See also

*
Beehive shelf A beehive shelf is a piece of laboratory equipment, usually of pottery, used to support a receiving jar or tube while a gas is being collected over water with a pneumatic trough. It is used so that when the gas emerges from the delivery tube in ...
*
Pneumatic Institution The Pneumatic Institution (also referred to as Pneumatic Institute) was a medical research facility in Bristol, England, in 1799–1802. It was established by physician and science writer Thomas Beddoes to study the medical effects of gases, know ...


Notes and references

{{reflist History of chemistry Gases Chemistry experiments