346 Obfcrvatlons on the Means of detefting 



2d, As it was neceflary that the detection fhould he of 

 fucli a nature as to he evident to thole acquainted with the 

 firit principles of chemiltry, I endeavoured to find it in the 

 relation which alkaline prufliates have with metallic folutions. 

 It is well known that they decompofe them all in confe- 

 quenee of that douhle affinity by which the pruflie acid 

 abandons its firft hafe to form with the metallic oxide an 

 intoluble prufliate, coloured according to the nature of the 

 metal. Setting out from this principle, 1 diffolved cryftal- 

 lized prufliate of potafh in diftilled water, and mixed this fo- 

 Jution with a part of the lufpeded wine. Having left this 

 mixture expofed to the air for twenty-four hours, and then 

 finding no other changes but a few atoms of pruiliate of iron, 

 very diftinguiihable by its blue colour, I considered myfelf as 

 authorized to announce that the wine in queition did not 

 contain the leaft particle of lead. 



3d, To give to this firft proof that degree of evidence of 

 which it is fufceptible, and to place the principles of it beyond 

 all doubt, I mixed another part of the fufpecled wine with a 

 Angle drop of the acetite of lead; to this mixture two drops 

 of the fame folution of prufliate of potaih (2d) were added, 

 and I immediately obtained a precipitate of a dirty white 

 colour, being the prufliate of lead, and proving in the fulleft 

 manner, that in the preceding experiment the fame wine 

 mult have given the fame precipitate if it had contained the 

 fmalleft particle of lead. 



4th, To thefe proofs and counter- proofs bv the prufliate 

 (2 and 3), that of the muriatic acid was added: the latter, 

 as is well known, feparates lead from its folutions under the 

 form of a muriate very little foluble; it did not difturb the 

 ;ranfparency of the fufpe&ed wine, nor produce any change 

 in it : this, then, {till tends to prove that the above fufpicion 

 was ill founded. 



5th, The proof by fulphuret of potafli, propofed long ago 

 as the fure means of detecting lead in wine, had been em- 

 ployed by the perfon above mentioned. A number of caufes, 

 well known, render this proof doubtful; and it is well known 

 that it is conclufive only when the prefence of the metal 

 alluded to has been proved by complete deoxygenation, 

 bringing back the oxide to the itate of metal. For want of 

 this verification, this proof has very often been the fource of 

 errors, the more ferious as the fufpicion to which they give 

 rife is odious. It was more than probable that the fame caufe 

 had in the prefent cafe produced the fame effect ; but it was 

 of importance to prove it, which was done as follows : 



The 



