Signs and Symbols

Martin Pitt explores the 19th century inventors of the symbols and calculations upon which modern science-based chemical engineering depends

MODERN science-based chemical engineering depends on the chemistry and physics developed in the 19th century. Concepts like elements, compounds and energy were all new, but simple ways of writing them to do calculations needed to be invented. Let’s look at the people who enabled mass and energy balances.

O is for oxygen, K is for potassium, Al is for aluminium, or is it aluminum?

When we write chemical formulae like H₂O, CO₂, NaCl, and then use them to write out chemical equations, we need to thank Jacob Berzelius (1779–1848), a Swedish chemist considered one of the four founders of modern chemistry. The others are Robert Boyle (1627–1691), of Boyle’s Law, John Dalton (1766–1844), who essentially gave us the theory of atoms, and Antoine Lavoisier (1743–1794), who changed chemistry from qualitative to quantitative and gave us the first list of elements. His quantitative measurements on combustion disproved the phlogiston theory, and showed that “dephlogisticated air” was in fact an element – oxygen.

Berzelius’s accomplishments are many and important, particularly the simple idea that all elements could be uniquely represented by one or two letters, and a subscript giving the number of elemental atoms in a group. Berzelius had originally proposed a superscript, but the printers preferred it below the line.

Lavoisier had named the element oxygène due to his mistaken notion that it was an essential component of acids, and using the Greek roots its name means acid (taste) maker. Accepting this notion, but preferring their own language, the Germans called it sauerstoff, and the Czechs called it kyslík.

Similarly, it was a French chemist who suggested nitrogène since it was found in nitrates, which the British thought a good idea, and Berzelius agreed. However, Lavoiser proposed azote meaning no life, and the French use this. The Germans, meanwhile, decided on stickstoff (suffocating stuff).

Berzelius’ notation helped cut through all these different names by giving chemists across the world a single formula. As atomic weights were established, chemical engineers would now be able to perform mass balances on chemical equations.

You’ll have noticed though, that symbol and name do not always go together because: all elements have to be different; there was a preference for Latin; and competition between British, German and French chemists.

British chemist Humphrey Davy (1778–1829) was the first to discover and isolate the elements he called sodium and potassium – soda and potash with a Latin ending. It had commonly been believed that the same element was present in the alkalis produced from these materials. However, German chemist Martin Klaproth (1743–1817) had early deduced that they were different and named the new one kali – from the Arabic which gives us alkali – and some thought the discovery was his.

The Germans decided that these two elements would be natrium and kalium, and Berzelius used these for his table of elements.

And what about Al? It is an element found in alum, so although not isolated till later, Davy named it alumium. After pedants pointed out that alum comes from the Latin word alumen – which changes to alumin on declension – and demanded an extra syllable, he renamed it aluminum, which goes well with the Latin names ferrum and stannum from which we get the symbols Fe and Sn.

Popular polymath Thomas Young (1773–1829) – of Young’s modulus and theory of light – said that Davy’s name had a less classical sound, and it would be better called aluminium, and this was generally adopted.

Noah Webster (1758–1843), on the other hand, used aluminum in his dictionary. Webster was responsible for most of the differences with American spelling, and disliked classical pedants.

H is for Enthalpy, S is for Entropy, and cold explains heat

Energy is such a familiar concept, that it is hard to believe the idea was only developed in the 19th Century. This physics concept and Berzelius’ notation led to quantitative mass and energy balances which are the foundations of our designs today.

The obvious person to thank is James Joule (1818–1889), after whom the SI unit is named. The prevailing view was similar to the phlogiston theory for combustion in that there was an invisible massless substance called caloric which transferred from flames, and transferred when something was heated or cooled. It had been challenged by an earlier experiment in which water was boiled by friction, and confirmed in precise experiments by Joule that mechanical work could be quantitatively changed into heat changes. Julius Von Mayer (1814–1878) in Germany did something similar around the same time, but his experiments were less careful. While subsequent writers credited both, Joule also had the idea that it was something to do with motions of atoms.

In 1853 William Rankine 1820–1872 (of the Rankine cycle and Rankine temperature) wrote: “In this investigation the term ‘energy’ is used to comprehend every affection of substances which constitutes or is commensurable with a power of producing change in opposition to resistance, and includes ordinary motion and mechanical power, chemical action, heat, light, electricity, magnetism, and all other powers, known or unknown.”

However, the person who is widely recognised as the father of thermodynamics is Sadi Carnot (1796–1832), who in 1824, at the age of 27 published Réflexions sur la Puissance Motrice du Feu – or Reflections on the Motive Power of Fire. The Carnot cycle was the first abstract and quantitative way of dealing with things like steam engines and their energy, or as he called it, caloric. In particular, he concluded that the maximum possible energy efficiency depended on the difference in temperatures: “The production of motive power is therefore due in steam engines not to actual consumption of caloric but to its transportation from a warm body to a cold body”.

He also considered air instead of steam as a working fluid and correctly interpreted volume changes in terms of what we now call entropy, named by Rudolf Clausius (1822–1888) in 1865. In honour of Sadi Carnot, the symbol S was adopted.

It was not until 1909 that the word enthalpy was coined, as a more precise definition than “heat energy”, though it was not widely used. In 1922, the year of IChemE’s founding, Alfred Porter (1863–1939) proposed, in the prestigious Transactions of the Faraday Society, that H should be restricted to enthalpy rather than heat in general. This important definition of heat was done in a paper on refrigeration. He pointed out that the Greek capital letter H is for eta. Sadly, the Greeks use E epsilon in spelling the word.

However, enthalpy first appears in the IChemE transactions as late as 1939, making its second appearance in 1946 in a splendid paper which pretty well defined chemical engineering thermodynamics, the terms and symbols we use.

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Next month I’ll be looking at the life of John W Hinchley – the forgotten founder of IChemE.

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For more on IChemE’s Centenary, including historical reflections from IChemE members, visit the dedicated website: www.chemengevolution.org