380 Count de Bourn on on Bardlglione, 



Integrant molecules of these substances is alone sufficient to prevent 

 our assenting to It; and It certainly cannot be that of the Abbe Haliy. 

 But does a real transition take place In this case, according to the 

 sense In which he uses the term Ep'igene P 



As an example of what he means to express by this word, he 

 quotes the transition of sulphuret of Iron, or pyrites, to the state 

 of hepatic Iron, which Is a reddish-brown oxide of that metal, 

 more or less compact In some parts, and frequently cellular In others. 

 He quotes also the transition of phosphate of lead in hexahedral prisms 

 to sulphuret of lead, or galena. 



In the first of these examples we can easily understand the nature 

 of the operation which takes place, and which consists In the actual 

 decomposition of the pyrites by the loss of the sulphur that was com- 

 bined with the iron : a decomposition probably produced by the 

 slow oxygenation of the pyrites, by which the sulphur is changed 

 into sulphuric acid, and is disengaged, leaving the iron in the state 

 of a brown oxide. 



The second of these example?, which offers more difficulty, may 

 however also be conceived, though without our being able clearly to 

 trace what was the primary or direct cause of the change. It appears, 

 with respect to this transition, that the decomposition, while it de- 

 prived the phosphate of lead of the phosphoric acid, probably by the 

 intervention of sulphuric acid, occasioned at the same time the de- 

 oxydation of the lead as well as of the sulphuric acid, which then 

 combined in the state of sulphur with the lead, and produced galena, 

 ■which is so moulded into the space occupied by the phosphate of 

 lead, that it has completely retained Its external form. 



In these two natural operations, so interesting and at the same time 

 so remarkable, the change which occasions the decomposition and 

 transformation of the substance begins at the surface, without in the 



