554 ANNUAL REPORT SMITHSONIAN INSTITXPTION, 19 63 



(Iraq). Later he proposed (1951) a series of chemical reactions to 

 explain the complex processes that are involved in the transformation 

 of nantokite to cuprite and alternately to atacamite. Essentially nan- 

 tokite rapidly hydrolizes and oxidizes when exposed to moist air and 

 forms simultaneously red cuprous oxide and basic cupric chlorides. 

 R. M. Organ (1963) has recently given a new review of the chemical 

 reactions involved in cliloride corrosion of copper, and described 

 various methods used at the British Museum Research Laboratory for 

 arresting it. One of these is to keep the antiquity in a dry atmos- 

 phere; the second is to effect complete removal of cuprous cliloride 

 by cathodic reduction at hight current density followed by intensive 

 washing; the third, which employs soaking for long periods of time 

 in changes of aqueous sodium sesquicarbonate, aims to convert cu- 

 prous chloride to harmless cuprous oxide. The fourth method makes 

 use of silver oxide powder to form an impermeable seal of silver 

 chloride over exposed cuprous chloride. This method is applicable for 

 arresting local areas of disease on objects which cannot be treated by 

 total immersion methods. 



The occurrence of chloride minerals on artifacts from areas of 

 fairly heavy rainfall, such as Europe and eastern China as noted above, 

 is interesting but puzzling. Captain Collins remarks in his discussion 

 of one of Vernon and Wliitby's reports (1930) that "Soluble chlorides 

 seem to cling to bronzes, though there may often be little chloride in 

 the surrounding region." This would be an interesting subject for 

 further investigation by soil chemists. 



COPPER SULFATES 



The bright green basic sulfate of copper corresponding to the min- 

 eral hrochantite^ Cu4(S04) (0H)6, is seldom reported on artifacts 

 although it might be expected on bronzes exposed to sulfate-bearing 

 waters. H. Otto (1961), however, reports the occurrence of this min- 

 eral on bronze artifacts found in German graves. The author (1933) 

 found e\'idence of basic copper sulfate in the green corrosion crusts of 

 a bronze statute of Nathan Hale in Hartford, Conn. The refractive 

 index of the green material indicated that the green was more like 

 antlerite, Cu3(S04) (OH)4[Cu3(S04) (0H)4], than brochantite but 

 unfortimately, X-ray diffraction methods for mineral identification 

 were not available at that early date to permit precise identification. 

 Some years ago the author examined the thin green corrosion crusts on 

 a number of bronze statues of the Garden Court of the Ringling Mu- 

 seum, Sarasota, Fla., and found that the alteration product gave an 

 X-ray diffraction pattern corresponding to brochantite. The sulfate 

 at Sarasota appears to originate in the hydrogen-sulfide-bearing water 

 used in the irrigation system in the garden. Likewise, a sample of 



