2C6 Analyjls. of the Emerald of VeAt. 



Thefe experiments, though not numerous, are fufficient to 

 prove, that the colouring matter of the emerald of Peru is 1 

 not iron, as announced by Klaproth, but that it is, on the 

 Other hand, the oxyde of the new metal which I difcovered 

 in the red lead of Siberia. One thing, however, which ought 

 to furprife thofe acquainted with the fagac'ity and accuracy 

 which the chemift of Berlin thews in his labours, and which 

 have gained him fo high reputation, is, that he did not ob- 

 ferve this fubftance, fo eafily to be diftinguifhed by a great 

 number of characlerifing marks, entirely different from thofe 

 exhibited by other minerals. I {hall now proceed to other 

 principles of the emerald. 



Exp. IV. The reader will recollect that the liquor of the 

 fecond experiment, deprived of its filiceous earth, was pre- 

 cipitated by cauftic potafli, and that the precipitate was, in 

 great part, re-diflblved by an exeefs of this alkali. This 

 folution was then fuperfatnratcd with the muriatic acid, and 

 carbonate of pbtafh ufed in commerce was poured over it. 

 This produced a very abundant precipitate, which, being 

 wafhed, and expofed to a. red heat in a filver crucible, weigh- 

 ed fifty-four parts. 



Thefe fifty-four parts were diflblved in the fulphuric acid ; 

 and the folution, by the addition of a little pOtafh at intervals, 

 gave, by feveral fucceflive cryftallifations, 149 parts of alum" 

 cryflallifed in octaedra, among which there were eight of 

 nine parts of the fulphatc of lime ; but as thefe 140 parts of 

 alum contained only about twenty-fix parts of pure alumine, 

 and as the mother-water, the taite of which was exceedingly 

 faccharine, gave no more alum by the addition of a new 

 quantity of potafh, I diluted it in water, and mixed with it 

 a folution of the carbonate of ammoniac, until there was an 

 exeefs. I fhook this mixture from time to time, for feveral 

 hours ; at the end of which the greater part of the precipi- 

 tate, which had been at firft formed, was diflblved. 



I then filtered the liquor, and collected on the paper the un- 

 diflblvcd matter, which, when wafhed and dried, weighed 



two 



