taken place in some antient alloys of copper. 57 



I have examined a select number of antient coins, pur- 

 posely chosen from the fine collection of Dr. Demetrio 

 Petrizzopulo, of Santa Maura, to whose kindness I am 

 indebted for them. The results too which they have afforded 

 are in conformity with the preceding. As this part of my 

 subject may be interesting to the antiquarian, as well as to 

 the chemical enquirer, I shall treat it a little in detail. The 

 very pale incrustations, consisting of a mixture of green and 

 white particles, contain a large proportion of oxide of tin, 

 and a little carbonate of copper, or submuriate of copper, or 

 both. They appear to owe their light hue to the accumula- 

 tion of the oxide of tin at the surface. The black incrusta- 

 tions owe their colour to the predominance of the black oxide 

 of copper, which is commonly mixed with a little protoxide 

 of the same metal, and a minute quantity of oxide of tin, 

 and of the carbonate and submuriate of copper. The coins 

 that I have examined with this crust have contained very 

 little tin. The bluish-green incrustations consist chiefly of 

 carbonate of copper, either without oxide of tin, or mixed 

 with a small proportion of this metal. The emerald-green 

 incrustations abound in the submuriate of copper, and the 

 red consist almost entirely of the protoxide of copper. These 

 two compounds I have never witnessed spread over the 

 whole of a coin, but more or less mixed with rusts of a 

 different kind, studding the surface in the form of little 

 crystalline elevations. 



It is natural to enquire — is there any connexion between 

 the chemical composition of the incrustations of antient coins, 

 and their texture ; some being remarkably smooth, and as 



MDCCCXXVI. I 



