Early chemical slide rules

The main page on chemical slide rules deals with the 20th century. In 2019, at the 150th anniversary of Mendeleev's periodic system, the UK Slide Rule Circle asked me if it could be extendedto 19th century.

In 1794 the French chemist Joseph Louis Proust discovered the law of definite proportions, stating that a given chemical compound always contains its component elements in a fixed ratio (by mass).[1,p.107] Soon other chemists found that chemical reactions take place between “simple multiples of the combining weights” or “simple volumes of the combining gases”.[1,p.124]

This can be explained by atomic theory, which had been lingering in the natural philosophers' minds since the ancient Greeks but was strongly revived by the English chemist John Dalton in the early 1800’s. The simple multiples are simple combinations of atoms.

William Hyde Wollaston rejected the atomic theory but expressed the simple proportions as chemical equivalents. These equivalents were essentially atomic or molecular[*] weights.[1,p.129] Wollaston presented the "Synoptic Scale of Chemical Equivalents", a slide rule with these equivalents, to the Royal Society in November 1813, which was published in the Philosophical Transactions in 1814.[2] Two months later the London instrument maker William Cary constructed an actual chemical slide rule from paper on mahogany.[3,4] The slide rule could have re-used the plates in the Philosophical Transactions but that does not seem to be the case. The logarithmic scales were based on oxygen = 10. The slide contains only numbers and the body contains the chemical markings on two scales (Figure 1). The numbers run from 10 to 320. For hydrogen a weight of 1.32 is shown, and for water 11.32, which reveals that for water Wollaston used the formula HO, instead of H2O or that he used for hydrogen the molecular weight of H2 instead of the atomic one. The slide rule contains 92 elements and compounds.
Around 1820, Dring and Fage, of London, made a long boxwood Wollaston slide rule, which is now in the Science Museum, London. In the 1830’s J. Newman, of London, made a chemical equivalent slide rule with only two scales.

Figure 1: Part of the Wollaston slide rule,[2]

The Deutsches Museum in Munich has chemical equivalents slide rules made by Joh. Barth. Trommsdorff around 1829[5] and Benjamin Scholz in Vienna in 1821. Both use oxygen = 10, hydrogen = 1.25 and water = 11.25. The Scholz slide rule runs from 10 to 380 and shows 98 elements and compounds.[6]

Also in the 1820’s, Martin Ehrmann of Vienna made a slide rule with oxygen = 10 and hydrogen = 1.25. The Whipple Museum in Cambridge has one of these showing 175 elements and compounds.

In 1815, William Prout tried to reduce all atomic weights to integers, with hydrogen having unit weight. He even went as far as stating that all elements are composed of aggregates of hydrogen.[1,p.129] It took some time before setting hydrogen = 1 was generally accepted.

The Scottish chemist David Boswell Reid published a manual for his improved slide rule of chemical equivalents, in which he showed a table with two columns of equivalents: one based on hydrogen = 1 and the other based on oxygen = 10. The actual scale is based on the first column, so with hydrogen = 1, but starts at 8 (oxygen), to save space. Hydrogen is shown as 10H and carbon as 2C.[7]

In 1827 the Dutch chemist Sibrandus Ezn. Stratingh published a book on stoichiometry in which he displays a linear slide rule and a circular slide chart for chemical equivalents. He used hydrogen = 1, oxygen = 8 and water = 9. His book also contains a table of atomic numbers according to various authors. It shows that many made attempts to use integers, while some still resorted to halves and quarters.[8]. Stratingh’s linear slide rule contains 120 compounds. His slide chart “Circulus Stoichiometricus Chemicus Elementorum et Compositorum ad usum Practicum et Analyticum” consists of 5 concentric rings, each of them subdivided in 2 or 3 rings with numbers, symbols or compound names ordered alphabetically(Figure 2). Note that Stratingh's circle did not use logarithmic scales.

Figure 2: Stratingh’s circular slide chart

A real logarithmic circular slide rule for chemical equivalents was presented as early as 1817 by Brugnatelli.[9]

Another logarithmic scale was used in a device patented in 1828 by Charles Hunnings Wilkinson, a physician from Bath.[10] An advertisement from1830 shows that it cost 10s, had a total scale length of 9 feet and contained 600 chemical combinations.[11] The “logometric scale of equivalents” was provided with “moveable pointals, or indexes, as in astronomical planispheres, [indicating] the relations of component constituents.”[12] That sounds like a very peculiar circular slide rule! Unfortunately, no surviving example of this disk are known.[13] One copy was donated to the library of the Yorkshire Philosophical Society[14] in 1828 but inquiries in 2019 at the Yorkshire Philosophical Society and the Yorkshire Museum did not result in retrieving this specimen.

Notes

[*] In early chemistry the terms “atom”, “molecule” and “element” were often interchanged.

The Oxford Museum of the History of Science owns several chemical slide rules. For instance W. Cary's Slide Rule For Chemical Equivalents of 1814 and John Newman's Slide Rule for Chemical Equivalents of 1830, both based on William Hyde Wollaston's design.

The Universiteitsmuseum Utrecht also owns an (undated?) Slide Rule For Chemical Equivalents made by Cary

See also William B. Jensen, “Two Chemical Slide Rules”, Museum Notes (May/June 2017) pages 1–3 and William D. Williams, “Some Early Chemical Slide Rules”, Bulletin for the history of chemistry, Vol. 12 (Fall 1992) pages 24–29

References

F.J. Moore, "A History of Chemistry", 3rd ed. , McGraw-Hill, 1939.
William Hyde Wollaston, “Synoptic Scale of Chemical Equivalents”, Philosoph. Trans. I (1814) page 1.
Conrad Schure, “The Wollaston Chemical Slide Rule”, J. Oughtred Soc. Vol. 5 No. 1 (Mar 1996) pages 22–23.
Louis J. Gotlib, “Chemical Slide Rules: Their History and Use”, J. Oughtred Soc. Vol. 21, No. 1 (Fall 2012) pages 8–15.
J[ohann] B[artholomäus] Trommsdorff, “Die Grundsätze der Chemie: mit Berücksichtigung ihrer technischen Anwendung”, Erfurt, 1829, pages 515-519.
Benjamin Scholz, “Anfangsgründe der Physik”, 3rd ed., Vienna, 1837, page 183 and plate 5.
David Boswell Reid, “Directions for using the improved sliding scale of chemical equivalents”, J. Dunn, Edinburgh, 1826, page 21-26.
S[ibrandus] Ezn. Stratingh, Ez., “Beknopt overzigt over de leer der Stochiometrie, dienstbaar gemaakt ter verklaring en aanwending van stochiometrische beweegbare cirkels”, Groningen, 1827, Chapter V. See also H.A.M. Snelders, "De geschiedenis van de scheikunde in Nederland. Deel 1", 1993, page 88.
[Brugnatelli], “Tavola Circolare degli equivalenti chimici”, Giornale di fisica, chimica, storia naturale, medicina ed arti del Regno italico, Pavia.Vol. 10 (Jan-Feb 1817) pages 28-39, Tavola 1 (two pages after page 80).
David Bryden, “English patents for scientific instruments in the Georgian Era…”, Proceedings IM 2018, Straford-upon-Avon, page 3.
C.H. Wilkinson, “An enquiry into the natural history, chemical properties, and medical virtues, of the rock oil, or green mineral naphtha, of Barbados, [etc.]”, London, Bath, 1830, last page.
John Murray, “A Manual of Experiments Illustrative of Chemical Science”, London (1833) pages 14–15.
John L. Thornton, “Charles Hunnings Wilkinson (1763 or 64–1850)”, Annals of Science, Vol. 23 (1967) pages 277–286.
Annual Report of the Yorkshire Philosophical Society, Feb 1828, page 51.

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