Telluric Screw and Law of Octaves

Béguyer de Chancourtois in 1862 was the first person to make use of atomic weights to reveal periodicity. He drew the elements as a continuous spiral around a cylinder divided into 16 parts. The atomic weight of oxygen was taken as 16 and used as the standard against which all others were compared. Chancourtois noticed that certain of the triads appeared below one another in his spiral. In particular the tetrad oxygen, sulfur, selenium and tellurium fell together, and he called his device the “telluric screw”.

The atomic weights of these elements are 16,32,79 and 128, respectively, and quite fortuitously they are multiples or near multiples, of 16. Other parts of the screw were less successful. Thus boron and aluminium come together all right but are then followed by nickel, arsenic, lanthanum and palladium. Chancourtois had discovered periodicity, but had got the frequency wrong. Not bad for a non - chemist - he was a geologist.

Another man who got nearer was John Newlands, Professor of Chemistry at the School of Medicine for Women, London. He chose a table of seven columns and entered his elements in increasing order of atomic weight. This arrangement produced some misalignments, but Newlands was sufficiently secure in his chemical knowledge to put similar elements in the same column even if it meant squashing two elements into some of his boxes. Newlands also recognised silicon and tin as part of a triad and predicted that there would be a missing element intermediate between these, with atomic weight of about 73. This predated Mendeleev’s predictions about germanium (which has an atomic weight of about 72.6) by about five years. However, Newlands did not leave a space for this missing element in his table of 1865. In fact, he left no vacant slots, which reveals that he had no appreciation of looking for an order that transcended his data.

By analogy with the tonic scale of seven musical notes and their octaves, Newlands called his discovery of periodicity the ‘Law of Octaves’. His efforts were criticised, indeed were publicly ridiculed, by members of the chemical fraternity and it was only in 1887, 18 years after Mendeleev’s work that Newlands’s contribution was recognised by the Royal Society, which awarded him the Davy medal.

Other Attempts

Other chemists who were sufficiently intrigued by atomic weights and the periodic occurrence of chemical properties also proposed repeating units of 1 (William Odling, 1864) and 15 (Lothar Meyer, 1868). The first of these, Odling, drew up a table of elements that bears a striking resemblance to Mendeleev’s first table. The groups are horizontal, the elements are in order of increasing atomic weight and there are vacant slots for undiscovered ones. In addition, Odling overcame the tellurium iodine problem, and he even managed to get thallium, lead mercury and platinum in the right groups - something that Mendeleev failed to do at his first attempt. However, we need lose little sleep over Odling’s failure to achieve recognition, since it is suspected that he, as Secretary of the London Chemical Society, was instrumental in discrediting Newlands’s efforts at getting his periodic table published.

The German chemist Julius Lothar Meyer also used Cannizzaro’s atomic weights to draw up a primitive table in 1864, but the more sophisticated version he produced in 1868 for the second edition of his textbook was not used and remained among his papers to be published only after his death in 1895. However, what Meyer did was to publish in 1870 a graph which plotted atomic volumes against atomic weights. This clearly showed the periodic changes of this property, with maximum atomic volumes at intervals of 7, 7, 14 and 15. With the inclusion of undiscovered elements this graph would have revealed the observed intervals of 8, 8, 18 and 18 of the first four rows of the modern table.

Meyer published too late to claim priority over Mendeleev but just in time to confirm that the latter’s discovery of the periodic table was based on sound chemical principles. Although Mendeleev published his tables in the new and obscure journal of the Russian Chemical Society, his paper was abstracted within weeks of its appearance into the German journal Zeitschrift für Chemie, and well before Meyer’s paper was published in December of that year, 1869.

© John Emsley

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