1835.] and Analysis of the Vanadiate of Lead. 37 



To determine the quantity, of muriatic acid, a new portion 

 was dissolved, and the solution was precipitated by nitrate 

 of silver. The products of the analysis were : — 



100-00 



Without dwelling upon the method of analysis adopted 

 by the French chemist, which was liable to great inaccuracy, 

 it may be sufficient to recapitulate the grounds upon which 

 he concluded that the acid contained in the mineral was 

 identical with chromic acid. 



1. The compound of the acid with lead was yellow. It 

 is now known that the chromate and vanadiate of lead are 

 both similar in their colour, but identity of colour is not 

 identity of composition. 



2. Nitrate of silver produced a red precipitate. Chro- 

 mate of silver varies in colour according to the temperature 

 at which it is precipitated ; being reddish brown when 

 thrown down from a hot solution, red with a tinge of 

 purple in its cold state, and carmine red with excess 

 of acid. 



The vanadiate of silver is likewise variable in colour ; 

 being yellow when neutral, but with excess of acid, deep 

 orange yellow. 



3. Nitrate of mercury produced a yellow precipitate. 

 Now chromate of mercury is purple or deep red, and 

 vanadiate of mercury is a fine lemon yellow. From this 

 fact it is evident, that the conclusions at which Des Costils 

 arrived were not authorized by the results of analysis, even 

 in reference to the slender claims which variety in the 

 colour of the precipitates of analogous acids has by itself 

 to determine difference of chemical nature. 



After the consideration of this analysis, it appears cer- 

 tainly extraordinary that the nature of the compound should 



