152 ESSAYS BIOGRAPHICAL AND CHEMICAL 



bromine, is a dark red liquid, but at a somewhat lower 

 temperature than that of boiling water it changes into a 

 red gas, with a smell similar to that of chlorine ; iodine, 

 though a black solid at the ordinary temperature, be- 

 comes, when heated, a violet gas. Like fluorine, they all 

 form compounds with hydrogen, of the formulse HF, HC1, 

 HBr, and HI ; these are colourless gases, soluble in water. 



Enough has been said to show that Newlands' method 

 of classifying the elements brings together in vertical 

 columns those that have similar properties. This method 

 was developed by a German chemist named Lothar 

 Meyer, and by a Russian named Mendeleeff, and it is now 

 universally acknowledged to be the only rational way of 

 classifying the elements. 



If we consider one of the horizontal rows, we shall also 

 discover a peculiarity. The number of atoms of the 

 elements which combine with an atom of oxygen gradually 

 alters ; and if they form compounds with hydrogen, the 

 same kind of regularity can be observed. For instance, 

 the elements of the first horizontal row given above form 

 the following compounds with oxygen and hydrogen : 



Name . . Lithium. Beryllium. Boron. Carbon. Nitrogen. Oxygen. Fluorine. 

 Formula of 



. Oxide . . Li 2 BeO B 2 3 C0 2 N 2 fi 

 Formula of 



Hydride . LiH unknown BH 3 CH 4 NH 3 OH 2 FH 



The elements of the subsequent rows show similar 

 regularity. 



Up till recently, no elements were known which refused 

 to combine with other elements. In 1894, however, Lord 

 Rayleigh and Sir William Ramsay discovered that 

 ordinary air contained such a gas, and they named it 

 'argon,' a Greek word which signifies inactive or lazy. 

 This gas had been overlooked because of its resemblance 

 to another constituent of the atmosphere, present in 

 nearly one hundred times greater amount nitrogen. 



