170 Experiments en Strontian and Barytcs, 



compound. — The method by which I examined whether the mineral under examination con- 

 tained b:irytes> was as follows. 



1. The fpar was decompofed by digeftion with carbonate of potafh, as in Mr. Clayfield's 

 experiments. The fubflance thus obtained, confifting of the earthy part of the mineral com- 

 bincJ with carbonic acid, I (hall call the precipitated earth. 



2. Nitric acid was gradually diluted with water, till it became capable of diflblving ftron- 

 tites but not barytes ; for to diflolve the latter, much further dilution is neceflary. The pre- 

 cipitated earth was wholly difiblved by this acid, which would have kft undiflblved any portion 

 of barytes. 



3. Barytes, in a pure and cauftic ftate, according to Dr. Hope (Edinb. Tranfaft. vol. iv.), 

 precipitates ftrontites and all other earths from muriatic acid. I cxpofed, therefore, to an in- 

 tenfely ftrong fire, a portion of the precipitated earth; and thus deprived it of its carbonic acid 

 fo completely, that it readily diflblved in hot water, and cryftallized on cooling. Now, if the pe- 

 culiar mineral iinder examination contained any barytes, this watery folution of its pure earthy 

 part, on being added to a folution of the precipitated earth in muriatic acid, would occafion a 

 reparation of ftrontites. On making the experiment, however, no precipitation took place, 

 which fhows that the watery folution contained no barytes, but confifted of pure ftrontites 

 only. The fame fad alfo proves that the muriatic folution contained neither lime, magnefia, 

 alumine, nor any of the metals, any one of which would have been precipitated by the ftrontitic 

 water. 



The' following experiments are, perhaps, worth relating, as they furnilh additional proof that 

 barytes and ftrontites are really diftin£t and peculiar earths. 



Dr. Hope, and I believe the generality of wruers on this fubjeft, affert that barytes (in con- 

 trad ill indion to ftrontites) is precipitated from muriatic acid by the Pruffiate of potafh. But 

 Mr. Kirwan, on grounds which he has not ftated, teftifies the contrary. *' Moft earths," he 

 obferves (Elements of Min. I. 3.), " are foluble in fome acid or another, and many in all 

 acids ; the Pruffian alkali can precipitate none of them from thefe folutions ; whereas it preci- 

 pitates all metallic fubftances except platina from their acid folvents. This forms a diftinit line 

 of feparation between earths and metals. The exception, formerly made in favour of barytic 

 earth, is now found to have arifen from a miftakc," As the decifion of this queftion is of fome 

 importance, from its influence on mineral analyfis, I determined to fatisfy myfelf of the truth by 

 the proper experiments ; the relation of barytes and ftrontites to the PrufEc acid, not having 

 been an objeft of attention either with Dr. Hope, M. Kiaproth, or MelT. Pelletier, Fourcroy, 

 and Vauquelin. 



I. Relation of Barytes to the PruJJic Acid. 



To a folution of cauftic cryftallized barytes in hot Avater, Pruffiate of iron, which had been 

 well waflied with boiling diftilled water, was gradually added, till it ceafed to be difcoloured. 

 The folution of barytes acquired a yellow tinge, refembling that of Pruffiated potaQi. It was 

 gently evaporated, and when cold, a number of cryftals had formed, which were flightly tinged 

 by iron, and appeared to be very minute rhomboidal parallelepipeds. 



Thdb 



