164 CHEMICAL DISCOVERY AND INVENTION 



and some others also fall together. But objection might very 

 well be raised to the position in which hydrogen is placed above 

 the halogens, also to the position of fluorine above the iron group, 

 the separation of sodium from lithium, and the close association 

 of the latter with potassium, beside other anomalies. The model, 

 however, shows very clearly the fundamental idea in the hypo- 

 thesis as to the origin and growth of the elements. They are 

 supposed to be formed successively by the condensation of the 

 primal matter or protyle, but it is not supposed that they were 

 generated one from the other, helium from preformed hydrogen, 

 lithium from preformed helium and so on. 



The hypothesis makes use of a sort of uniformitarian principle 

 in the assumption that the whole of the elements have been 

 brought into being by the operation of the same physical con- 

 ditions acting uniformly from first to last. We now know from 

 the products of radio-active change that some elements must 

 have been formed not by a process of condensation of protyle or 

 anything else, but by the reverse operation, namely, the dis- 

 integration of more complex masses. It must also be borne in 

 mind as one of the results of modern work that the elemental 

 atoms appear to contain in every case positive and negative 

 constituents which are held together by their mutual attraction. 

 It does not appear therefore that the simple condensation or 

 polymerisation of a mist-like material is a sufficient account of 

 what must have been a more complex process. 



Of the known elements the metals have more characters in 

 common than any of the others ; they all appear at the cathode 

 when they are deposited from their compounds in the process of 

 electrolysis, they are good conductors of heat and electricity, 

 and are generally malleable and ductile. They vary in density 

 from lithium, which is the lightest solid known, to gold, platinum, 

 iridium, and osmium, which are at the other end of the scale. 

 This is nearly in the order of their atomic weights. Moreover in 

 many families the metallic positive chemical character develops 

 and becomes more evident in passing from the members of lowest 

 atomic weight to those of higher atomic weight. This is illus- 

 trated in such cases as the alkali metals potassium, rubidium, 

 caesium, and the metals of the alkaline earths, calcium, strontium, 

 barium. The family likeness is so strong as to be suggestive of 

 the existence in the metals of some common constituent or a 

 similar arrangement of the particles or corpuscles of which we 



