130 Mr Haidinger on the changes xvhich take place 



sometimes crystallized, particularly on the concave sides. 

 There were some white patches also which I did not then 

 examine. During his residence in the Ionian Isles, Dr John 

 Davy has paid much attention to similar changes which 

 have taken place in ancient Greek armour and coins. He 

 found * that the substances forming green, red, and white 

 spots on the surface of these articles, consisting of alloys of 

 copper and tin, were carbonate and submuriate of copper, oc- 

 tahedrons of the protoxide and pure metallic copper, and ox- 

 ide of tin. In several instances there was no metallic copper 

 formed, and the protoxide was blackened by an admixture of 

 peroxide. Since it cannot be supposed that the substances 

 formed on the surface of these bronze articles were deposited 

 from any solution, Dr Davy infers that an internal movement 

 of the particles must have taken place, caused by the influ- 

 ence of electro-chemical powers. Dr Davy's opinion, that 

 such considerations will explain many phenomena occurring 

 in the mineral kingdom, is shown to be perfectly correct by 

 many facts observed in nature. In the native copper I 

 never could observe any such changes, though I have examin- 

 ed a great number of specimens with the view of discovering 

 them ; but we have probably to attribute to the admixture of 

 tin, and the electro-chemical action dependent upon the contact 

 of the two metals, the greater disposition of bronze to form 

 new compounds with the elements contained in the atmosphere 

 and in water. 



There are several species, in the composition of which sul- 

 phuret of copper enters as one of the most important ingre- 

 dients, as the prismatic copper-glance, or vitreous copper, and 

 the octahedral and pyramidal copper-pyrites, or the variegated 

 copper and copper-pyrites. All of them are more or less 

 subject to successive changes in their chemical constitution, 

 while the form in some cases remains, and in others is entirely 

 lost. Mr Allan is in the possession of a very interesting and 

 numerous series of copper-ores, which he collected chiefly in 

 the summer of 1824, on a journey in Cornwall, in which I 

 had the pleasure of accompanying him. This series has given 

 me an opportunity of noticing several peculiarities which had 

 not been mentioned before by mineralogists. 



• Phihsqphtcal Transactions fdr 1928, pi A9,'- ' ' 



