32 Preparation and Haliludes ofPruJfialt ofPot-afh. 



Rather more of the pruffiate of barytes fliould be employed than is required to decompofc 

 the carbonate. After digefting the mixture about half an hour, filtre the liquor, which, 

 when gently evaporated, will fhoot into beautiful cryftals of pruffiate of pot-a(h. Thefe 

 cryftals contained, in one inftance, 24 per cent, of oxyde of iron ; but of this oxyde a con- 

 fiderable part may be feparated, by digefting the folution, before evaporating it, with a 

 little acetic acid (radical vinegar.) The acetic has this advantage over all other acids, that 

 its combination with pot-alh affords a fait incapable of cryftallizing; and which cannot, 

 therefore, mix with the cryftals of pruITiated pot-afli. 



The carbonate of barytes, which is thus re-generated, may be referved ; and may be 

 again fitted by calcination for the fame procefs. 



With the view of deciding the queftion in difpute, I added to a folution of pruffiate of 

 pot-a(h prepared, in the above manner, a folution of muriated barytes, • No precipitation 

 enfued; nor was the tranfparency of the mixture in the leaft degree difturbed. This 

 experiment, therefore, in addition to thofe before related, convinced me that I had been 

 deceived ; and that Meffrs. Meyer and Klaproth were correct in denying the precipitation. 

 Happening, however, to examine the jar, about half an hour afterwards, I obferved that 

 a number of fmall cryftals had formed on its inner furface ; and thefe, on allowing the 

 mixture to ftand a few hours, increafed confiderably in number. I next mixed the two 

 folutions in larger quantity, with the fame-refult. No Immediate effe£t was apparent ; but 

 after a few hours, an abundant crop of fmall cryftals had formed at the bottom and on 

 the fides of the jar. Thefe cryftals had the following charadter : 



1. They diffolved very fparingly in cold water, viz. in about the proportion of a quarter 

 of a grain to each ounce. 



2. Hot water diffolved them more readily, but ftill only in very fmall proportions. 



3. From thefe watery folutions fulphate of pot-afh, or fulphuric acid, precipitated 

 fulphatc of barytes ; and on adding the fulphate of iron to another portion of the folution, 

 an abundant precipitation of Pruffian blue occurred. 



4. The cryftals were totally diffolved by dilute muriatic acid ; and the folution gave 

 decided marks, to the proper tefts, of containing prufliated barytes. 



5. When heated ro rednefs in a filver veffel, they grew black and loft their form. On 

 adding dilute muriatic acid to this coal, an effervefcence enfued, and the folution was 

 muriated barytes. 



The foregoing chara£lers are peculiar to the fait termed pruffiate of barytes, the 

 formation of which, under the above circumftances, proves, beyond all doubt, that a 

 double eledtive affinity is exerted between muriate of barytes and pruffiate of pot-afli. In 

 this refpeft, barytes differs from other earths, and approaches the metals. 



The above experiments furniftied a clue, which led to the explanation of the con- 

 tradictory properties, obferved, at different times, in the precipitate from muriated barytes 

 by pruffiate of pot-afli. In trials, which I have fince made, it has uniformly happened, 

 that common pruffiate of pot-afh has preaipitated muriate of barytcsi When the 



fupernatant 



