62 Ford and Bradley — On Hydro.:! m-ite. 



the analytical methods used, a third analysis was made on 

 massive material in the Brush Mineral Collection from Mal- 

 lidano, Sardinia. 



The analytical method adopted was extremely simple. The 

 water was determined directly by heating the mineral in a 

 closed glass tube, collecting the water in the upper part of the 

 tube and weighing it, making the proper corrections for the 

 presence of CO, in the tube. The zinc oxide was determined 

 by igniting the mineral, driving off all the water and carbon 

 dioxide and weighing the residue. This method was tested by 

 dissolving the residue and redetermining the amount of the 

 zinc oxide after the precipitation as sulphide from a formic 

 acid solution. The two results agreed. Careful tests were 

 made for the presence of other possible elements but with 

 negative results. The carbon dioxide had to be determined by 

 difference. The analyses by Bradley follow : 



Good Springs, Nevada. 



Crystalline Theory for 



Crystals material 2ZnCO s .3Zn(OH) 2 Sardinia 



ZnO -. 75-58 74-67* 74-14 73 72 



CO, [15-78] [16-41] 16-03 [15-47] 



H o 8-64 8-92 9-83 10-81 



100-00 100-00 100-00 100-00 



* Average of two closely agreeing determinations. 



These results do not agree as closely with the assumed 

 formula as could be desired. It is to be regretted that more 

 material was not available in order that the portions used 

 could have been larger and direct determinations made of all 

 constituents. Still, no other formula could be proposed which 

 would agree more closely with the analytical results except one 

 that would be very complicated and improbable. Considering, 

 therefore, the unfavorable conditions of the analysis and the 

 very strong argument provided by the close physical resem- 

 blance between aurichalcite and hydrozincite, it is felt that the 

 formula given must be correct. 



The conclusion of the investigation, therefore, is that 

 aurichalcite and hydrozincite are practically one species, only 

 distinguished from each other by the introduction into the 

 former of some copper oxide which replaces an equivalent 

 amount of zinc oxide. 



Mineralogieal Laboratory of the Sheffield 

 Scientific School of Yale University, 

 New Haven. Conn., March 22, 1916. 



