METALS AND METALLOIDS 691 



do not exist in the free state, but can pass from one compound to 

 another in chemical interchanges. 



The typical benzenoid or aryl radical is phenyl C 6 H 5 , obtained 

 by the abstraction of one hydrogen from the aromatic hydro- 

 carbon, benzene. This radical, again, is only known in combina- 

 tion. 



Perhaps in passing I should attempt to define the inorganic 

 portion of my title. The metals are those elements which can 

 function as simple cations in electrolysis and which do not 

 furnish volatile hydrides, i.e. compounds with hydrogen. The 

 metalloids are a small group of elements having certain metallic 

 characteristics and, in addition, the property of yielding vaporis- 

 able hydrides like the non-metals. Arsenic, antimony, and 

 tellurium may be regarded as metalloids, and possibly also 

 boron and selenium, although the last two are much more closely 

 allied to the non-metals than to the metals. 



In many instances chemical research has progressed along 

 utilitarian lines. The employment in medicine of various plant 

 extracts has encouraged investigations on alkaloids and other 

 active products of vegetable life. The art of dyeing has led to 

 the study of natural and artificial colouring matters, lakes, and 

 mordants. But the activities of pioneers have never been 

 restricted by purely utilitarian considerations, and if science is 

 to continue its healthy and beneficial growth it is to be hoped 

 that these activities will always be afforded the widest scope. 

 Many laboratory investigations, at first apparently quite devoid 

 of any practical utility, have led to results of fundamental 

 importance from both the theoretic and practical standpoints. 

 The pioneering experiments of Cavendish on the fixation of 

 atmospheric nitrogen is a classical example, and I hope to 

 show that the early study of organic derivatives of metals and 

 metalloids is another case in point. Of no branch of human 

 activity can it be predicted with greater certainty than of 

 chemistry, " Cast thy bread upon the waters and thou shalt 

 find it after many days." 



1. Early Researches 



So singular are the properties of the first discovered organo- 

 metallic compounds that in taking up their study chemists 

 appeared to be turning their backs on the realities of ordinary 

 terrestrial phenomena. It would tax the genius of a Jules Verne 



