Analogies observed in Chemical Unions. 361 



instances, although we can easily trace the geometrical ar- 

 rangement, they are more or less irregular in their details. 

 In other cases, we do not find that mathematical forms are 

 actually assumed ; but we observe a certain structui-e of the 

 shapeless mass, which admits of separation in particular direc- 

 tions, corresponding to fixed geometrical figures, similar to 

 those which other bodies are found actually assuming ; and the 

 same substance is often found at one time in the actual ma- 

 thematical form, and at another in the shapeless mass possess- 

 ing the regular structure when divided. We can have no he- 

 sitation in considering this cleavage as rudimentary crystalli- 

 zation. 



When we come to examine the objects of inorganic nature, 

 whether natural or artificial, with reference, not to structure, 

 but to chemical qualities, we can still discover the relation to 

 some type or standard, and a progi'ession in the degree of ap- 

 proach to this standard in diflPerent instances. In many cases, 

 although it is not difiicult to discover the type on which a 

 compound has been formed, yet the result is an imperfect one, 

 with reference to that type. 



If we turn our attention to the leading chemical characters 

 of elementary bodies, we find that their combinations with 

 oxygen may be either bases or acids ; and, in like manner, the 

 compounds which they form with hydrogen, may be either 

 bases or acids. We have examples of hydrogen bases in 

 ammonia, in several hydro -carbons, and in phosphuretted-hy- 

 drogen, all of which can be shewn to possess, in a greater or 

 less degree, the character of bases. The combinations called 

 salts are usually formed between oxygen acids and oxygen 

 bases, or between hydrogen acids and hydrogen bases, and, 

 more rarely, between the acids of the one class and the bases 

 of the other. 



It appears to be certain that ammonia possesses, per se, the 

 character of an alkaline base. In the gaseous state, when per- 

 fectly dry, it still acts on dry test papers ; and when perfectly 

 dry ammoniacal and carbonic acid gases are mixed together, 

 the white salt formed by their union has a strong ammoniacal 

 odour, and yields ammonia when heated with recently ignited 

 quicklime, subliming in part unchanged. Its solution in 



