142 CLASSIFICATION OF ELEMENTS. 



tural families in which the elements may be arranged, and 

 observing the links by which the different groups themselves 

 are connected; these classes not being abruptly separated, 

 but shading into each other in their characters, like the classes 

 created by the naturalist for the objects of the organic world. 



CLASSIFICATION OF ELEMENTS. 



The First class comprises four elementary bodies : oxygen, 

 sulphur, selenium, tellurium. The three last of these elements 

 exhibit the closest parallelism in their own properties, in the 

 range of their affinities for other bodies, and in the properties 

 of their analogous compounds. They all form gases with one 

 atom of hydrogen, and powerful acids with three atoms of 

 oxygen, of which the salts, the sulphates, seleniates and tel- 

 lurates are isomorphous ; and the same relation undoubtedly 

 holds in all the corresponding compounds of these elements. 



Oxygen has not yet been connected with this group by a 

 certain isomorphism of any of its compounds, but a close cor- 

 respondence between it and sulphur appears, in their com- 

 pounds with one class of metals being alkaline bases of similar 

 properties, forming the two great classes of oxygen and sulphur 

 bases, such as oxide of potassium and sulphuret of potassium ; 

 and in their compounds with another class of elements being 

 similar acids, giving rise to the great classes of oxygen and 

 sulphur acids, such as arsenious and sulfarsenious acids. They 

 farther agree in the analogy of their compounds with hydrogen, 

 particularly of peroxide of hydrogen and persulphuret of 

 hydrogen, both of which bleach and are remarkable for their in- 

 stability ; and in the analogy of alcohol and mercaptan, which 

 last may be considered as an alcohol with its oxygen replaced by 

 sulphur. This class is connected with the next by manganese, 

 of which manganic acid is isomorphous with sulphuric acid^ 

 and consequently manganese with sulphur. 



Second Class. This class comprises magnesium, calcium, 

 manganese, iron, cobalt, nickel, zino, cadmium, copper, hydro- 

 gen, bismuth, chromium, aluminum, glucinum, vanadium, zir- 

 conium, yttrium, thorinum. The protoxides of this class, in- 

 cluding water, form analogous salts with acids. A hydrated 

 acid, such as crystallized oxalic acid or the oxalate of water, 

 corresponding with the oxalate of magnesia ; hydrated sulphu- 



