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 magnetic properties, hydrocarbon radicles, etc.; in fact, a full list is to be found in the index of the Principles of Chemistry—a book which gives the views of Mendeléeff on most subjects. The work has been translated into nearly all the languages of Europe.

Concerning the element argon discovered by Lord Rayleigh and Sir William Ramsay, Mendeléeff wrote to the author on 18/30 March 1895, as follows:—

A mon avis l'argon (molécules) est au N3, formée l'azote N2 avec dédagement de chaleur, au A6, si A = 6·6 de 1re sérié. La première hypothèse est, pour moi, la plus probable, comme j'avais déjà communiqué dans la Société Chimique Russe.

When Mendeléeff delivered the Faraday Lecture at the Royal Institution in 1889, he said: "The law of periodicity enables us to perceive undiscovered elements at a distance, which formerly were inaccessible to chemical vision; and long ere they were discovered new elements appeared before our eyes possessed of a number of well-defined properties. &hellip; " Since then argon, helium, neon, xenon, metargon, krypton, radium, and possibly other forms of matter have been, and may be, discovered, throwing wondrous light on the structure of material things, but by no means invalidating Mendeléeff's famous periodic law—that is, as far as we know at the present time. It is possible that the law may be modified as time rolls on. The evolution or mutability of the elements may throw new light on the nature of the chemical element—the law of combination in simple proportions, and