INERT CONSTITUENTS OF THE ATMOSPHERE. 581 



THE INEET CONSTITUENTS OF THE ATMOSPHEEE. 



By Professor W. RAMSAY, 



UNIVERSITY COLLEGE, LONDON. 



^T^HE discovery of an element always awakens interest; for the total 

 -*- number of the known elements does not exceed seventy-five, and 

 all the various forms of matter which exist on this globe are necessarily 

 composed of these elements. An element, as is well known, is the 

 ultimate constituent of a compound; and with only a limited number, 

 Nature has provided us with that enormous wealth of minerals, of 

 vegetables and of animals, all of which have as their constituents 

 two or more of these elements. 



These elements, however, must not be regarded as isolated entities, 

 each self-dependent, having no relations with its compeers; on the 

 contrary, all the elements exhibit certain connections with their neigh- 

 bors; and there is to be traced an orderly progression from one class 

 of elements, strongly electro-positive in character, metallic in appear- 

 ance, very inflammable when heated in the air, and at once attacked 

 by water, to another class, highly electro-negative, transparent, unat- 

 tackable by oxygen, and without perceptible action on water, through 

 a number of connecting links, each of which serves to soften the 

 transition. 



These elements have been arranged in series, and it is by consider- 

 ing the method of arrangement that our interest is awakened. The 

 earliest attempt to make such an arrangement antedates the very idea 

 of the conception of an element. For the division of all matter into 

 metal and non-metal is one which is lost in the mists of antiquity. 

 The word %etal' is derived from the Greek verb juezaVAco, I search; 

 and that verb is said to be derived from //ira and dXXa, signifying 

 'after other things.' As it was recognized that elements are constit- 

 uents of more complex matter, a conception first emphasized by Boyle, 

 and as the distinction became clear that matter which resists de- 

 composition must be classed as elementary and, after a century and 

 a half, a number of elements were recognized, it was obvious that a 

 number of them might be grouped in classes. Take, for example, the 

 elements chlorine, bromine and iodine, all colored, strongly smelling 

 substances, sparingly soluble in water and forming compounds barely 

 distinguishable from each other in appearance or by a cursory inspec- 

 tion; or take such a group as the metals of the alkalies, lithium. 



