, 5* A't'if Combination difcovered In Zaffir: 



This property is that of the arfenic acid. This combination 

 iri known under the name of arfen'wte of copper. 



3d, Sulphate of copper mixed with this U(|nor gives a pre- 

 cipitate of tlie fame colour as the amnioniiire of that metal. 

 The arfenious acid polVcU'es this property alfo, though not in 

 fo high a degree as the pretended cobaltic acid ; but a finiilar 

 precipitate maybe obtained by making ufe of artificial arfcni- 

 ate of cobalt. The refulls then are the fame: no difference 

 can be perceived between them. 



4th, It precipitates nitrate of (liver wliite. The arfenfc 

 acid poflelfcs this propertv. 



5th, It precipitates nitrate of mcrcurx of a (Iraw colour. 

 It is well known that the arfenic acid exhibits the fame pha-- 

 iiomenou. 



6th, It precipitates liuic water in a white eoagulum in- 



• foluble in water, but not infoIui)le in excels of acid, as Rru- 

 'gnatelli fays; finceit, indeed, rcdifjolves with the fame facility 



• in the pretended cobaltic acid as in the arfenic acid. The 

 "'error of Brugnatelli, in my opinion, arofc from his not having 



cmploved a fufficieut qnantitv of acid. 



7th, It precipitates acelite and muriate of barvtes. I af- 

 "fured myfelf that this precipitation arofe from fome atoms of 

 fulphuric acid contained in the acid called cobaltic. The 

 arfeniatc of cobalt alfo difguifes its folutions. 



8thj With tin£ture of galls newly made it forms an abun- 

 dant yellowifli precipitate. It is well known that the arfenic 

 acid produces the fame phieuomenon. 



9th, This lad experiment feems to have been confidered 



by Brugnatelli as the mod charaAeridic of his cobaltic acid: 



he obferved that alcohol fejiarated his folution from its aque- 



. ons folutiun, and the arfenic acid, dilfolved in alcohol, pof- 



fcfled the fame properly: bv thcfe procelfcs he obtained his 



• conca'te acid. 'I'his proj)ertv of the cobaltic acid at firll 

 aftoniflied me; but, prefuming that I might find an explana- 

 tion of it bv examining the acid thus precipitated, I fubjected 



- it to the following experiments : 



I, When luated on charcoal at the flame of the blowpipe 



• it emitted white vapours, which were evidently arfenic. 



II. A fniall portion; healed with borax, communicated to 

 it a violet colour. 



■ ■ III. This acid, being precipitated onlv by alcohol, I exa- 

 mined the liquor after having feparatt'.d it bv the filter. Sul- 

 phurated hydrogen produced in it an abundant yellow preci- 



"^ prt:ite, found to be fulphuret of arfenic. 



W. The aqid, when feparated, was fcarcely foluble in 

 water, '••j ^ •'. • 



' - . V. When 



