president's address. 11 



Dobereiner, Dumas, and others, John Newlands in 1862 and the follow- 

 ing years arranged the elements in the numerical order of their atomic 

 weights, and published in the ' Chemical News ' of 1863 what he 

 termed his law of octaves — that every eighth element, like the octave 

 of a musical note, is in some measure a repetition of its forerunner. 

 Thus, just as C on the third space is the octave of C below the line, 

 so potassium, in 1863 the eighth known element numerically above 

 sodium, repeats the characters of sodium, not only in its physical 

 properties — colour, softness, ductility, malleability, &c. — but also in 

 the properties of its compounds, which, indeed, resemble each other very 

 closely. The same fundamental notion was reproduced at a later date 

 and independently by Lothar Meyer and Dmitri Mendeleeff; and to 

 accentuate the recurrence of such similar elements in periods, the 

 expression ' the periodic system of arranging the elements ' was 

 applied to Newlands' arrangement in octaves. As everyone knows, 

 by help of this arrangement Mendeleeff predicted the existence of then 

 unknown elements, under the names of eka-boron, eka-aluminium, and 

 eka-silicon, since named scandium, gallium, and germanium by their 

 discoverers, Cleve, Lecoq de Boisbaudran, and Winckler. 



It might have been supposed that our knowledge of the elements 

 was practically complete ; that perhaps a few more might be discovered 

 to fill the outstanding gaps in the periodic table. True, a puzzle existed 

 and still exists in the classification of the ' rare earths, ' oxides of 

 metals occurring in certain minerals ; these metals have atomic weights 

 between 139 and 180, and their properties preclude their arrangement 

 in the columns of the periodic table. Besides these, the discovery of 

 the inert gases of the atmosphere, of the existence of which Johnstone 

 Stoney's spiral curve, published in 1888, pointed a forecast, joined 

 the elements like sodium and potassium, strongly electro-negative, 

 to those like fluorine and chlorine, highly electro-positive, by a series 

 of bodies electrically as well as chemically inert, and neon, argon, 

 krypton, and xenon formed links between fluorine and sodium, chlorine 

 and potassium, bromine and rubidium, and iodine and caesium. 



Including the inactive gases, and adding the more recently dis- 

 covered elements of the rare earths, and radium, of which I shall have 

 more to say presently, there are eighty-four definite elements, all of 

 which find places in the periodic table, if merely numerical values be 

 considered. Between lanthanum, with atomic weight 139, and tan- 

 talum, 181, there are in the periodic table seventeen spaces; and 

 although it is impossible to admit, on account of their properties, that 

 the elements of the rare earths can be distributed in successive columns 

 (for they all resemble lanthanum in properties), yet there are now 

 fourteen such elements; and it is not improbable that other three will 

 be separated from the complex mixture of their oxides by further work. 



