12 



slum, the other half remaining in the compound, whereas the smallest 

 particles of nitric acid either exchange the whole or none of their 

 hydrogen for potassium. 



This fact is expressed in the simplest possible manner by the 

 statement that the smallest indivisible particles of sulphuric acid 

 contain two atoms of hydrogen, whilst those of nitric acid only 

 contain one. Thus it is, that whereas the equivalent weights of the 

 two acids are the quantities which contain the same amount of basic 

 hydrogen, their atomic weights must be in the proportion of two 

 equivalents of sulphuric to one of nitric acid. The simplest expres- 

 sion for an atom of nitric acid being empirically NO 3 H, we shall 

 accordingly represent an atom of sulphuric acid by the formula 

 SO 4 H 2 . In like manner, an atom of common phosphoric acid, 

 being tribasic, is expressed empirically by the formula PO4 H 3 . The 

 labours of Messrs. Laurent and Gerhardt greatly contributed to the 

 establishment of these results, which are uncontroverted. 



We have hitherto been accustomed to resort very freely to ima- 

 ginary distinctions of form and arrangement of matter to explain the 

 differences of properties ; but of late years an opposite tendency has 

 arisen, and chemists have felt the necessity of reducing their language 

 and ideas to simpler and more consistent forms. This necessity was 

 first felt in the most complex, i. e. the so-called organic part of che- 

 mistry. But the simplifications thus introduced have proved to be 

 equally applicable to the inorganic part of the science ; and their 

 introduction is calculated to disengage, for the consideration of sub- 

 stantial differences of composition, the attention which has hitherto 

 been absorbed by imaginary distinctions of form. Being unable to 

 express the constitution of compounds without some formal artifice, 

 we shall be able to see and compare their substantial differences 

 most easily when all unnecessary variations of those formal artifices 

 are eliminated. The success of this operation of course depends on 

 our finding one form sufficiently general to replace the special and 

 limited forms now employed. 



In some papers published in the Journal of the Chemical Society 

 two or three years ago, I endeavoured to show that the constitution 

 of salts may be reduced to the type of water ; that acids and bases 

 being, truly, acid salts and basic salts, are perfectly conformable to 

 the same principle ; and that, amongst other things, the difference 



