440 Doctor Clark to Professor- Mitscherlic/t. 



gards the portion of them that corresponds with potassium 

 in the analogous compounds containing this metal ; for 

 that potassium is, in every such compound, substituted by 

 ammonium (N 2 H 8 ), I hold to be a point as well established 

 as any within th& range of ascertained chemistry. Quite 

 consistent with such a view of the aminoniacal salts, how- 

 ever, is either of the forementioned opinions respecting the 

 oxygen salts. The recommendation of simplicity and ana- 

 logy belongs to the newer opinion, which regards the basis 

 of Glauber's salt to be the same as that of common salt, 

 the basis of nitre to be the same as that of sulpho-cyanide 

 of potassium, the basis of green vitriol to be the same as 

 the basis of what used to be called green muriate of iron. 

 More especially does this appear, when, on adding tartaric 

 acid to solutions of salts having so much resemblance as 

 nitre and the sulpho-cyanide of potassium, we obtain cream 

 of tartar in such case, or when, on adding caustic potash, 

 or sulphuret of potassium, or yellow prussiate of potash, 

 or the red prussiate, to solutions resembling each other, in 

 colour, taste, and in action on the air, as do solutions of 

 proto-sulphate, and proto-chloride, and proto-sulphocyanide 

 of iron, we produce, by each re-agent, a like precipitate 

 from all these three solutions ; for surely it is hard of be- 

 lief, that such likeness of character and of action all pro- 

 ceeds from bodies having no likeness of constitution. Ob- 

 stacles, however, are in the way of our adopting the newer 

 opinion, were it only for the difficulties that must occur in 

 the application of a new doctrine, in all its details, to the 

 numerous compounds that any doctrine relating to salts 

 must embrace. And, until some discovery be made, incon- 

 sistent with either opinion, both must remain open to the 

 choice of chemists, like two roads leading to the same 

 place, an old and a new, where the new way, although the 

 straighter and the more level, is yet avoided by the con- 

 course of travellers, as hajjpening to be the rougher, and 

 less agreeable and easy, from the single circumstance of 

 its being new. 



These things I recall on the present occasion, conceiving 

 that, if the suggestion be well founded, that oxymanganate 

 ofbarytes is analogous in constitution to the sulphate of 

 silver, and to the waterless sulphate of soda (wherein is 



