354 Materials for a History of the Prussicrfes* 



in the ammoniacal products of the blood. It even seems 

 that, like phosphorus, it can be fixed in the charcoal, but 

 not in the iron which it contains ; for the smell of the 

 aromatic hydrogen mentioned above gives no indication of 

 the presence of sulphur. 



We easily recognise the simple prussiate by its double 

 alkalino-bitter taste, and bv the aroma with which it fills 

 the mouth. It precipitates in yellow the solution of copper, 

 and does not give blue with that of red oxide ; but it pre- 

 cipitates them in oehrey yellow, as a pure alkali would do*. 

 Lastly, it gives blue with an ordinary solution of sulphate 

 of iron, because there is at first constituted triple prussiate : 

 afterwards it cives white or blue prussiate of iron. If the 

 prussiate be black, it is because the alkaline hydro-sulphuret 

 introduces hydro-sulphuretted oxide into it ; but we get rid 

 of it with some drops of acid, and the prussiate of iron ap- 

 pears alone. The simple prussiate cannot be well preserved 

 except in a closed flask. Scheele has shown, that the car- 

 bonic acid is sufficient for separating it from the potash 

 while its affinities are feeble; when the black oxide is not 

 united with it, concentrated it refuses to crystallize and 

 runs into a mass, in which, however, we distinguish some 

 saline laminae. 



This prussiate is the test liquor proposed by Scheele. Its 

 utility in analysis is not limited, since all solutions the iron 

 in which is at the maximum, (and this is most frequent,) 

 -are not, as he has himself shown, by any means sensible to - 

 this reagent. In order to employ it carefully, we must bring 

 back to the minimum a part of the oxide of the solutions : 

 this is not always easy, nor without danger of increasing the 

 difficulties of the experiment. ( 



Its Decomposition. — The aqueous solution of this prussiate, 

 on being boiled, abandons a part of its acid : which demon- 

 strates sufficiently that this combination is neither solid 



* In a memoir I wrote upon Sigena stone, I announced this union as being 

 probable; but I now find it was a mistake. A sulphate of iron which I had 

 hyper-oxidated by the nitric acid, and which, nevertheless, retained some 

 remaius of black oxide, deceived me; and Scheele, whom I contradicted in 

 thi. sfspect, saw more clearly than I did. 



nor 



