Chemical slide rules

Dating slide rules by the chemical data they provide.

Slide rules are not the core of my collection, which consists mainly of mechanical calculators and planimeters. Yet I could not resist the temptation to buy a Nestler Chemiker 33 slide rule. This slide rule contains scales with molecular masses to assist chemists in synthesis and analysis. Similar slide rules have been produced by Hemmi (number 257), Keuffel and Esser (4160), Faber (Chemie), Unique (O), ALRO (a disk, see picture), Aristo (a disk with number 630) and Concise (number 600). Slide rules with the same function were already made in the nineteenth century.[1]

At the back of my Nestler is a table of atomic masses. I tried using those masses to date the slide rule.

ALRO Chemie showing atomic masses from J. Am. Chem Soc. 1948 (Courtesy of Otto van Poelje)

Atomic masses

The determination of atomic masses is not an easy task. One of the reasons being that chemists need a mass that is averaged over all the isotopes of an element, weighted by their natural abundance. In the late nineteenth century the resulting discussions led to the formation of national commissions for the establishment of atomic masses. Such committees are known in England, Germany, Spain, Switzerland and the United States. In 1903 an International Commission began publishing data on atomic masses while the national committees were still active. The International Committee became part of the International Union of Pure and Applied Chemistry (IUPAC) in 1920. Since then, the biennial IUPAC reports on atomic masses can be considered as a global standard. A convenient list of atomic masses as published over the years by the International Commission can be found on the web.[2]

In the Netherlands, the values of the International Commission were used pretty early: the Chemical Yearbook in 1905 already contained the International Atomic Masses.[3] I do not know whether this was also true in Germany, because Germany still had a national commission at that time.

If, nevertheless, we assume that Nestler always adapted the table, and perhaps the scales as well, to the new values of the International Commission, we can use the table to date Nestler Chemiker slide rules.

For 19th century slide rules for chemical equivalents, see the separate page "Early chemical slide rules"

Nestler 33 and 0330 tables

My Nestler 33 gives an arsenic (As) mass of 74.93. This value is used by the IUPAC from 1931 to 1934. Furthermore, Nestler gives a iodine (I) mass of 126.932, a value which was published by the IUPAC in 1925 and was replaced by 126.92 in 1933. The masses given for Lead (Pb, 207.22) and Uranium (238.14) were only used from 1931 to 1937. So my Nestler 33 dates probably from 1931–1933.

On the Nestler 33 in the Slide Rule Catalogue (number 1864) not all masses are easy to read, but what could be deciphered points to the year 1909 or 1910. The mass of zinc deviates from the 1909 value: the slide rule gives 65.37, but the International Commission starts giving that value in 1910. The mass of chromium differs from the 1910 value: in 1910 the International Commission changed this mass from 52.1 to 52. If we compare the official values of 1912 with those on the slide rule, we find the following differences (in brackets the masses on the slide rule) Cr 52 (52.1), Sr 87.63 (87.62), V 51.0 (51.2). The values for P 31.04 (31) and Pt 195.2 (195) are wrong but that could be caused by improper rounding-off by Nestler. Moreover, is seems that Titanium (Ti) and Tantalum (Tl) are switched in this table. The table seems to state: Ti 204, Tl 48.1, which is alphabetically correct, but is numerically incorrect. Peter Hopp[4] states that the Nestler 33 was made from 1915 to 1955. According to Guus Craenen[6] production took place between 1910 and 1955. The dating of this Nestler confirms the data of Guus.

An easy way of distinguishing old and new Nestler 33's: old ones miss the black tick mark for Ti and use "Cy" for cyanide. Newer ones show the Ti tick mark, and use "CN" for cyanide. The scales of newer Nestler 33's also contain more compounds.

The Nestler 0330 with Slide Rule Catalogue number 1972 is to date as follows: The mass of iron (Fe) is 55.85, but was officially 55.84 before 1940. The mass of Copper (Cu), 63.57, was replaced in 1947 by 63.54. This slide rule probably dates from the period 1940–1947. That is inconsistent with the production data of Anagit, the material the Nestler 0330 was made of. Anagit was used after 1955.

Concise 600 tables

The Concise 600 (Sama & Etani) disc calculators come with a separate table with atomic masses. These tables have a copyright date and they therefore serve as a test of the dating method. The table used is the Michael O'Leary Memorial Edition Concise 600 shows a copyright date of 1976. Our dating method yields 1975–1978. The slide rule itself is of course of a much later date.

An older Concise 600, with copyright date 1968, may be dated 1967–1968, according to the masses of magnesium and lithium.

Nestler scales

Can we also see the changes in atomic masses on the scales? For most of the masses this is not possible: the changes are so subtle that the scale resolution of a slide rule is insufficient. But it should work for Antimony (Sb): between 1903 and 1925, a value of 120.2 was used, and that differs significantly from 121.77, the value that was introduced in 1925. The mass of Palladium (Pd) was changed from 106.7 to 106.4 in 1955 and should cause a visible difference between the scales of an early and a late Nestler 0330. But Palladium only appears in PdJ2 on the scales of the Nestlers. This reduces the relative mass difference by two-thirds, and the lines seem to appear at the same place.

Figure 2 shows a part of the old Nestler 33 (Slide Rule Catalogue number 1864), a flipped mass scale of the Nestler 0330 (Slide Rule Catalogue number 1972), a "normal" scale of the 0330, and again the mass scale of 0330, but in its normal orientation. At the bottom is the flipped mass-scale of my Nestler 33 (AdM). The large silicon mass difference between the oldest Nestler and the other two is indicated with an arrow. At the far left one can see that the difference between the mantissas of the mass of Sb2 (2.404) and Mg (2.433) is larger on the old rule than on the later rules (Sb2 = 2.4354 and Mg = 2.432). There should be a visible difference between the masses of Selenium (Se) on my Nestler 33 (AdM) and the Nestler 0330 (1972), 78.96 vs. 79.2, but Se is only present in the table at the back and is not shown on the mass scales.

Keuffel and Esser 4160 scales

The K&E 4160 slide rules have no table, so they can only be dated by their scales. On the early rules described by Clark McCoy,[7] with production number 161 from 1915–1916 and number 207 from 1916–1921, the mark of Antimony (Sb, 120.2) coincides with the Carbon (12.0) mark. In the K&E 4160 from 1925–1927, with serial number 183656, we see distinct Sb and C marks (Figure 3). This reflects the official mass change of Sb from 120.2 to 121.77, which took place in 1925.

Note that the newer K&E is simplified. This is probably done to avoid confusion. On the old K&E's the marks of Ag and N2O5 coincide, but it looks like the label "Ag" belongs to the Pd-mark, and the label "N2O5" might belong to the B-mark, while it is not immediately clear which mark the label "B" refers to.

Figure 1: Part of the table on my Nestler 33

Figure 2: Comparing three Nestlers

Figure 3: Comparing two K&E 4160's

Test your slide rule

An online tool helps you to date your own chemical slide rule by the table of atomic weights.

Simulations

Some chemical slide rules are simulated online:
ALRO Chemie, Hemmi 257.

Challenge

Can slide rules for other disciplines also be dated by their tables? That depends on two things: the table values should have been subject to considerable changes in the last century, and there must have been an authority that regularly published "valid" values. I think a lot of data we find on the back of slide rules, like the density of wood and concrete, does not meet those conditions. Or is that a prejudice caused by the chauvinism of an (ex-)chemist?

References

1. The Oxford Museum of the History of Science has several chemical slide rules, for instance W. Cary's Slide Rule For Chemical Equivalents of 1814, Wollaston's Chemical Slide Rule of 1820 and John Newman's Slide Rule for Chemical Equivalents of 1830. The Deutsches Museum in München displays a 19th century chemical equivalents slide rule by Benjamin Scholz, which looks a lot like Wollaston's slide rule, but with the scale extended to 380.
2. See also William D. Williams, "Some Early Chemical Slide Rules", Bulletin for the history of chemistry, Vol. 12 (Fall 1992) page 9.
3. History of the recommended atomic-weight values from 1882 to 1997: a comparison of differences from current values to the estimated uncertainties of earlier values, Pure Appl. Chem., Vol. 70, No. 1, (1998) pages 237–257.
4. W.P. Jorissen et al., Chemisch Jaarboekje 1905–1906, Amsterdam: D.B. Centen.
5. Peter M. Hopp, "Slide Rules – Their History, Models, and Makers", The Astragal Press, 1999.
6. Guus Craenen, "Innovation und Qualität – Die Rechenschieber von Nestler in ihrem internationalen Umfeld", Soest, 2001. See also the Journal of the Oughtred Society, Vol. 11 No.1 (Spring 2005) p.38-46
7. Clark McCoy, K&E 4160 Family of Slide Rules

A Dutch version of this paper appeared in MIR 44, April 2007

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