THE MODERN THEORY OF CHEMICAL TYPES. J 55 



diate constituents. In the above example the 24HO may be driven off by heat, 

 but not by electricity simply; and from other considerations it is impossible to 

 decide from analysis alone whether water is an acid or a base, as it possesses, 

 according to the suhstance with which it is combined, each of these characters; 

 in oil of vitriol it is a base HO SO3 ; in hydrate of potassa, an acid KO HO. 



There is still another method of imagining the grouping of. the atoms in a 

 complex atom to form a binary compound. This involves the cnsence of the 

 radical theory. 



SO3 docs not redden litmus nor form salts with bases ; its compound with 

 HO (oil of vitriol) possesses this property. We may imagine this acid to be 

 HO, SO3, according to the principles just laid down ; or to be H SO4, a binaxy 

 compound, in which H is + and SO4 is — . If for hydrogen we substitute potas- 

 sium or any metal, we will have sulphate of potassa or the salt corresponding to 

 the metal. SO4 is, therefore, a compound radical in the sense in which the word 

 has been employed in chemistry, although it has not been isolated. "When 

 water and anhydrous sulphuric acid are brought together, this compound radical 

 is generated by the decomposition of water in the manner illustrated above. 



It is, however, more particularly in the case of the bases that the theory of 

 compound radicals has been developed. 



The example of ammonia illustrates an inorganic compound radical ; if, in- 

 deed, it may at present be called inorganic. 



The gas ammonia XII3 (in a manner analogous to that of anhydrous sulphuric 

 acid) acquires basic properties only by the action of water; NH3, H0 = NH4 0. 

 NH4 is the compound radical, ammonium. It has never been isolated ; it is an 

 hypothetical group of atoms playing the part of a metal. 



The following table illustrates the parallelism existing between compound 

 and simple inorganic radicals : 



Comp. radical ammonia. Simple radical potassa. 



+ - + - 



NH4 + ") Oxide. ^ K + 



NH4 + S ! Sulphide. J K + S 



^\U + CI f Chloride. ) K -f CI 



NIi4 + SO4 3 Sulphate. (. ^ + ^^4 



When organic chemistry began to be developed, the compounds first studied 

 were those containing different proportions of carbon, hydrogen, and oxygen, 

 together with a few containing nitrogen. These were studied in their analogies 

 to inorganic compounds, and the assumption of a large number of organic 

 radicals became imperative. For example, if ether (C4 H5 O) were the oxide 

 of a radical (C4 H5) called ethyl, the compounds of ether could be brought into 

 comparison with those of oxides of the different metals, (C4 H5,) being a com- 

 pound organic radical, which group of atoms plays the part of a metal, thus : 



Ethyle (C4H5) 



Ether (04115)0 



Alcohol (C4H5)0, HO 



Chloride of ethyle (C4H5)G1 



Nitrate of the oxide of ethyle (C4H5) 0, NO5 



Acetate of the oxide of ethyle (C4n5)0,(C4H3)03 



Sulphate of the oxide of ethyle (C4ll5)0, SO3 



Sulphovinic acid (C4Hr,)0, SO3 + HO, SO3 



Sulphovinate of the oxide of zinc (C4H5)0, SO3 -\- ZnOSOa 



Potassium K 



Potassa KO 



Hydrate potassa KO, HO 



Chloride potassium KCl 



