148 ESSAYS BIOGRAPHICAL AND CHEMICAL 



iron-rust, the answer must be: No. The properties of 

 rust are wholly different from those of iron; no iron 

 particle can be detected in the rust by any tests which are 

 suitable for the recognition of the metal as such. But if 

 it is meant that iron if exposed to damp air changes into 

 rust, and that by suitable treatment metallic iron can be 

 extracted from rust, then the answer must be in the 

 affirmative. 



The fact that an element, when it combines with other 

 elements, entirely loses its original properties, led to the 

 not unnatural supposition that it should be possible to 

 change an element into another, or to transmute it. Long 

 before the notion of ' element ' was formulated by Boyle, 

 innumerable attempts had been made to convert one 

 metal into another ; and, indeed, it would appear on the 

 face of it to be much easier to transmute lead into silver 

 or gold than to convert it into the yellow earthy powder 

 which it becomes when heated in air. For on the old 

 doctrines, the properties of gold its lustre, its ductilit} 7 , 

 its melting in the fire were much more similar to those 

 of lead than the properties of litharge or oxide of lead, 

 produced by heating lead to redness in air. After Boyle's 

 day, however, it gradually came to be seen that certain 

 substances resisted all such attempts to change them into 

 others without increasing their weight. For example, all 

 changes in nature not of a temporary and evanescent charac- 

 ter which iron can be made to undergo, are accompanied 

 by an increase in the weight of the iron ; they are produced 

 by the combination of iron with other elements, and the 

 addition of another element to iron invariably increases 

 the weight, for the weight of the combining element is 

 added to that of the iron, and the result is a compound 

 differing in properties from iron. It was slowly discovered 

 that about seventy substances must be classed as elements 

 the minimum number of the present day is seventy- 



