

160 ARRANGEMENT OF THE ELEMENTS IN COMPOUNDS. 



Cyanogen was the first recognised member of the class of com- 

 pound radicals, of which the number known to chemists is con- 

 stantly increasing, and which appear to pervade the whole 

 compounds of organic chemistry. In combining with simple 

 bodies, radicals act the part of other simple bodies, such as 

 metals, chlorine, oxygen, etc., which they replace in compounds. 



Constitution of salts. Of the supposed combinations of binary 

 compounds with binary compounds, the most numerous and 

 important class are salts. Sulphate of soda is commonly viewed 

 as a direct combination of sulphuric acid and soda, each pre- 

 serving its proper nature in the compound ; and so are all similar 

 compounds of an acid oxide with a basic oxide. An oxygen 

 acid is allowed to exist in them, and they are particularly dis- 

 tinguished as " oxygen-acid salts/' But an opinion was pro- 

 mulgated long ago by Davy, that these salts might be consti- 

 tuted on the plan of the binary compounds of the former class, 

 and their hydrated acids on the plan of a hydrogen acid ; a view 

 which is supported by many analogies, and has latterly had a 

 preference given to it by some of our leading chemical authori- 

 ties. It is, therefore, deserving of serious consideration. 



One class of acids, the hydrogen acids, and the salts which 

 they produce with alkalies, are unquestionably binary com- 

 pounds, and were assumed by Davy as the types of acids and 

 salts in general. Hydrochloric acid is composed of two ele- 

 ments, chlorine and hydrogen, and with soda it forms water 

 and chloride of sodium, thus : 



TT j 1,1 -j /Hydrogen. . -^ Water. 

 Hydrochloric acid < Chlorine s^ 



~ , / Oxygen. vX*X. 



\ Sodium. . __X*, Chloride of sodium. 



the hydrogen of the acid being replaced by sodium in the salt 

 formed. Hydrocyanic is another hydrogen acid, of which 

 cyanide of sodium is a salt. In general terms, a radical (which 

 may be either simple or compound, like chlorine or cyanogen) 

 forms an acid with hydrogen, and a salt with sodium or any 

 other metal. 



Hydrated sulphuric acid, which consists of sulphuric acid and 

 an atom of water, HO + SO 3 , is represented as a hydrogen acid 

 by transferring the oxygen of the water to the sulphuric acid, 

 to form a new radical, SO 4 , which is supposed to be in direct 

 combination with the remaining atom of hydrogen, as H + SO 4 . 

 In sulphate of soda, the oxygen of the soda is in the same 



