An Element of Order
Julius Lothar Meyer and his not-so-famous periodic table. (Yale University, Harvey Cushing/John Hay Whitney Medical Library; Edgar Fahs Smith Collection, University of Pennsylvania Libraries)
In 1870, the year the German states merged to form one nation as a result of the Franco-Prussian War, Meyer was a chemistry professor at Karlsruhe Polytechnic Institute. He contributed his medical skills to his newly born nation by setting up a temporary hospital for those injured in the war. Like Mendeleev, he saw his world politically and economically transformed, but unlike Mendeleev, he was never part of public life. “He was a classic university professor,” says Gordin. “He taught large courses, advised lots of students, wrote textbooks, and lived a very bourgeois life.”
While Meyer’s life may have followed that of a bourgeois professor, in the chemistry world he was an oddball: he speculated, including on the physical reality of the atom and on how matter was built and bonded. Despite this, remarks Gordin, if you asked almost any 19th-century chemist which one of the two was more of a chemist’s chemist, it would be Meyer: “He does things properly. He’s a little funky on theory and has a lot of speculations, but he knows how to discipline and control them.”
In the 1860s the interests of both men coalesced around the periodic behavior of many of the known elements. Today we understand the periodic table as saying something fundamental about matter. Each row of the table moves from left to right as electron shells fill up; each element has one more proton than the one before it. But in the 1860s electrons had yet to be discovered, and only a few chemists, such as Meyer, were rash enough to speculate on the atom’s physical reality.
Making a Periodic Table
Systems to order the elements came into existence six times during the 1860s. Even before tables were created, people found relationships among elements, such as certain triads where the atomic weight of the middle element is the average of the ones on either side. And it was clear to chemists of the time that certain elements came in natural families, like the halogens—fluorine, chlorine, bromine, and iodine.
All the systems put the elements in order of increasing atomic weight, which is why they cluster in the 1860s. Before that time chemists did not have accurate atomic weights; some were off by a factor of two, being measured as twice as heavy or twice as light as what we now recognize as their true weights. Uranium, for example, was thought to weigh something on the order of 120, instead of 240. Only after the first major international chemistry conference, held in Karlsruhe in 1860 and attended by both Meyer and Mendeleev, did chemists standardize atomic weights. Once that happened, chemists found it far easier to order their elements.
A French mining engineer named Alexandre-Émile Béguyer de Chancourtois created the very first system of ele-ments in 1862. Instead of the now-familiar grid, he used a helix and called his system the telluric screw: Béguyer de Chancourtois drew a diagonal line on a sheet of graph paper and placed the elements along the line by increasing atomic weights, then wrapped his sheet around a cylinder. Dropping a vertical line down the sheet linked elements with similar properties. “There were experimental errors and not all the elements sit on a straight line, but it’s a very interesting system,” says Gordin. “But no one cared; no one even remembered what he did until the 1870s, when there was a priority dispute over the periodic table.”
In 1864 Meyer published the first edition of Die modernen Theorien der Chemie and included a table of 28 elements arranged by increasing atomic weight and divided into six families by valence. So, for example, sulfur was placed just below oxygen in the valence-2 column (valence determined how elements combined with each other). Tin was placed below silicon in the valence-4 column, though intriguingly Meyer left a gap between silicon and tin, as if for a shadow element. “Meyer’s distinctive quality for most historians and chemists is that he had gaps [in his periodic system] and chose not to predict,” says Gordin. “And, therefore, he somehow failed because predicting is obviously what you should do when you have gaps in a system.” But in the 1860s filling the gaps was not at all an obvious move.
Mendeleev also encountered gaps when assembling his first table in 1869—three gaps, to be precise, each of which he filled with a question mark and rough estimate of atomic weight before moving on to the next element. Mendeelev viewed his system as a generalization about matter rather than an earth-shattering invention. It allowed chemists, especially those teaching students, to organize large amounts of information in a small amount of space. In essence it was a teaching tool with no connection to theory. Mendeleev initially developed the table for his textbook Osnovy khimii (Principles of Chemistry). When it came time to present it to the Russian Chemical Society in March 1869, Mendeleev was off in the countryside inspecting cheese makers, leaving a friend to introduce his table to the world.