ON THE PaUSSlC AND PRUSSOUS ACIDS. 345 



this acid; and that from the well-known affinities of its 

 three elements, added to the circumstances under which it 

 is formed, it can scarcely be thought that it does." This 

 difference of opinion implies a want of some decisive ex- 

 periments, which may set the question for ever at rest, and 

 these which I am going to relate I am induced to think are 

 of that description. 



Some time back, I proposed to myself the discovery of Attempt (o<li?- 

 a method of preparing a triple prus^iate of potash, in a ^^J^J^j '1^'"^,'^^^^ 

 pure state, which should be free from the objections to of. preparing 

 which the processes in general use are subject. In reflect- J^f notr^h'^'"^ ^ 

 ing on the means most likely to attain this end, it occurred 

 to me, that I should succeed, if I decomposed prussiateof 

 iron by double elective attraction rather than by single; 

 employing, instead of a pure potash, this alkali in combi- 

 nation with a substance uniting the properties of solubility 

 when combined with potash, strong attraction for oxide of 

 iron, and insolubility when united to this oxide. The only 

 substances I could think of possessing all these requisite 

 properties were the succinic acid and sulphur. As the 

 high price of the former precluded its use for this purpose, 

 I determined to employ the latter. I therefore took one Sulplmret of 

 ounce of dry sulphuret of potash, and one ounce and a |y°^,^^^ "^.^'^^ 

 half of the best prussian blue, previously well washed and blue. 

 powdered, and put them into a Florence flask, two tliirds 

 jilled with distilled water; a disengagement of sulphuretted 

 hidrogen of ammonia, and of caloric, immediately took 

 place. The materials were boiled slowly together for three 

 hours, occasionally replacing the water which evaporated. 

 The whole was then thrown on a filter ; what remained on 

 the filter was black, and consisted of sulphuret of iron, and 

 nndecomposed prussiate of iron. The liquid, that passed 

 through, I found on trial to consist of triple prussiate of 

 potash, and hidrogurctted sulphuret of potash. In order to The solution 

 complete the decomposition of the latter, I boiled the J'q"i(^ JrcSVus'ian 

 again, for the same time as before, with another half ounce blue 

 of Prussian blue, and when cold filtered it. The filtered 

 liquid (A) was now nearly colourless, and free from hidro- 

 guretted sulphuret. On pouring a little of it into a solution 

 of oxisulphatc of iron, I was very much surprised to find 



that 



