150 ESSAYS BIOGRAPHICAL AND CHEMICAL 



or hydrochloric acid, consists of one part by weight of 

 hydrogen combined with 35J parts by weight of chlorine ; 

 and as it is believed to contain one atom of each element, 

 it follows that an atom of chlorine is 35 J times as heavy 

 as an atom of hydrogen. On the same principle, the 

 relative weights of the atoms of other elements were 

 determined. And so, taking the weight of the lightest 

 atom, hydrogen, as unity, the atom of nitrogen weighs 

 14 times as much, of oxygen 16, of iron 56, of lead 207, 

 and so on. 



Attempts to classify elements according to their proper- 

 ties soon followed ; and at first the divisions were some- 

 what arbitrary. The non-metals were distinguished from 

 the metals by their lack of lustre, their feeble power of 

 conducting heat, and the fact that their oxides when 

 mixed with water generally formed acid substances, while 

 those of the metals were earthy, insoluble powders. Cer- 

 tain of the metals, which either do not unite with or are 

 difficult to unite with oxygen at a red heat, were called 

 ' noble ' metals ; others, which are at once attacked by 

 water, such as sodium and potassium, and which give 

 soapy liquids with a harsh taste, were named ' metals 

 of the alkalies/ and so with the rest. In 1863, however, 

 Mr. John Newlands, a London analyst, was successful in 

 arranging the elements in groups, so that each element 

 in a horizontal column showed analogy with others in the 

 same column. He found that by writing the names of 

 the elements in horizontal rows, beginning with the one 

 of lowest atomic weight, each eighth element possessed 

 properties similar to those of the elements which pre- 

 ceded or followed it in the vertical columns. And in 

 general the composition of the compounds of such 

 similar elements was similar. The first two lines of 

 such a table are reproduced here, so as to show what is 

 meant : 



