58 Dr. Davy's observations on the changes which have 



it were polished, preserving admirably the original impression 

 of the die ; whilst others are rough and deformed ? I am 

 disposed to reply in the negative, not having yet discovered 

 such a connexion ; excepting thus far, that the protoxide of 

 copper, and its submuriate, frequently appear in minute 

 crystalline elevations rising above the surface of the coin. 

 Generally, I suspect the difference of texture in question 

 depends on other circumstances, and very likely in different 

 degrees of rapidity of operation of the mineralizing cause. 



It is a curious question for consideration, the manner in 

 which the crystalHne structure is acquired exhibited by these 

 incrustations ; and still more so, how crystals are formed, 

 especially such as were discovered on the helmet, and on the 

 adhering calcareous deposit. There being no reason to sup- 

 pose deposition from solution, are we not under the necessity 

 of inferring, that the mineralizing process witnessed in its 

 effects, depends on a slow motion and separation of the 

 particles of the original compound ? and, must we not con- 

 clude, that this motion is connected with the operation of 

 electrochemical powers ?* Supposing the oxides first formed 

 upon the bronze in a state of negative electricity, with respect 

 to the metal, their agency, in a long course of ages would 

 be to separate the least oxidable metal, the copper, in its 

 pure form ; and all the changes are such as may be accounted 

 for from agencies of the same kind, but of different intensity. 

 And may not similar explanations be given of other like 



* The separation of the copper from the tin in the bronzes found in the ancient 

 cities destroyed by volcanic eruptions, must be referred to another source ; namely, 

 the crystallizations dependent upon degrees of heat a little below the point of fusion 

 of the alloy. 



