On a Difficulty in Isomorphism. 439 



Every chemist is aware, that the prevailing opinions re- 

 specting the constitution of oxygen salts — that sulphate of 

 soda, for instance, consists of sulphuric acid and soda — 

 were adopted long before the elements of such salts were 

 known to the extent that they now are. We are old enough 

 to remember how much the ideas of chemists were stag- 

 gered at the discovery of the metals potassium and sodium, 

 especially when it was found that common salt, while it 

 could readily be proved lo contain sodium, could not, by 

 any device of ingenuity, or industry of investigation, be 

 proved to contain soda. However much habit may since 

 have worn off surprise, the published researches of the 

 ablest chemists of the time evince, that the discovery of 

 those metals was conceived to be little consistent with what 

 were then, and what with many still are, the received no- 

 tions respecting ammonia and the ammoniacal salts. The 

 extravagant assumption of a combination so improbable, 

 ideal, and untangible, as what was called the hydro-chlo- 

 rate of soda, was but a proof, that chemistry had, on a 

 sudden, outgrown the old garment of theory, that had 

 once afforded to the whole body of its facts, a fit and ample 

 covering, but which was now so inadequate that it could not 

 be drawn over the nakedness of any one part, without 

 making bare some other. 



Subsequent researches, belonging more definitely to our 

 own time, seem to have had more effect in unsettling for- 

 mer doctrines respecting the salts, than in establishing any 

 new doctrine. But the opinions entertained by chemists 

 respecting the constitution of oxygen salts appear to be 

 chiefly two. In the instance of sulphate of soda, one of 



these opinions regards the basis as the alkali soda (Na S), 



the other as the metal sodium (Na S). When the basis of 

 the salt is conceived to be soda, oil of vitriol must be re- 

 garded as a compound of sulphuric acid and water (HH S); 

 but when the basis of the salt is conceived to be sodium, 



the same liquid must be regarded as a hydrogen acid (H- S). 

 Whatever uncertainty there may be as to which of these 

 views is to be preferred, none exists, in my mind, as to the 

 constitution of the ammoqiacal sails, so far at least us re- 



