a real Acid of Cvlalt. 103 



Brugiiatelll himself suspected that his cobaltic acid was 

 arsenical acid ; but he was so deceived by certain ccmsidera'- 

 tions that he paid no further attention to this suspicion, 

 and neglected to verifv it by experiments : oii the contrary, 

 he was""convinced of the reality of his cubaltic acid on the 

 tbiiowing grounds : 



1st, The arsenic;- 1 acid does not precipitate silver from 

 its solution, but the cobaltic acid docs. 



2d, The arsenical acid dc::omposes lime water, and the 

 precipitate is redissolved by the addition of new arsenical 

 acid or lime water ; the cobaltic acid decornposes lime 

 water, and the precipitate produced dissolves neither in a 

 new quantity of cobaltic acid nor in a new addition of lime 

 »vater. 



3d, Neither acetlte of lead nor muriate of barytes is de- 

 composed by the arsenical acid ; on the other hand, boih 

 these salts are immediately decomposed by the cobaltic acid- 

 4th, The arsenical acid dissolves very well in alcohol : on 

 the other hand, liquid caljaitic acid, when united with pure 

 alcohol, is immediatriv precipitated in a solid form. 



\<1 hat weight these four arguments have in regard to the 

 existence of the cobaltic acid,"{ shall now examine. 



In regard to. the first, the assertion of Bru2:nate!li is di- 

 rectly ccnti-ary to experience. The arsenical acid certainly 

 precipitates silver from a solution of arsenical acid, and of 

 a brovu colour; but with a small quantity of this acid anil 

 fi large quantity of muriatic acid, white. This appears from 

 what has been already said, and has been proved bv my 

 pwn experience. Against the justness of the assertion which 

 Brugnarelli gives as^the second ground for the existence of 

 the cobaltic "acid, nothing, sd far as the question relates to 

 pure arsenical acid, can be objected ; but that the union of 

 arsenical acid, ammonia, and cobalt, produces with lime 

 water the same phtenomena as Brugnatclli observed in re- 

 gard to his cobaltic acid, — that is to say, of precipitating 

 lime water without dissolving the precipitate produced by 

 the addition of more of the precipitating mattor,-^has been 

 already seen in the ninth experiment (3). Hence it follows 

 that the second ground is ccjually unsatisfactory and incon- 

 clusive. ■ 



The ground which Brugnatclli assumes as the third proof 

 of his cobaltic acid, is in part incorrect, and contrary to all 

 experience : every chemist knows that acetate of lead is vcr\' 

 easily decomposed ; bv which means a very abundant preci- 

 pitate of arseniate of lead is produced, which is exceedingly 

 difTicuIl of solution on ;i new addition of nrscnical acid. It 



is 



