S. L. Penfield — Chemical Composition of Aurichalcite. 109 



I. Moravicza in Banat. 

 II. 



III. Campiglia, Italy. 

 IY. Sardinia. 



V. Theory according to Belar for CuC0 3 , 3Zn(OH) 2 . 



VI. Theory according to the original formula 2RC0 3 , 3R(OH) 2 , Cu : Zn = 2 : 5. 



I. II. III. IY. Y. VI. 



Loss on ignition 24-91 26-78 26-50 22-97 23-30 26-04 



H 2 13-53 . 12-84 9*90 



CO, [11-38] 10-46 16-14 



CuO -.. 20-39 21-43 * 20'20 15-58 18-91 20'79 



ZnO 54-70 53-57 55-51 58-72 57'79 53-17 



10000 101-78 102-21 97-27 lOO'OO 100-00 



Water was determined directly only in the first of these 

 analyses, and C0 2 by deducting H Q from the loss on ignition, 

 or indirectly by deducting the sum of all the other constituents 

 from 100 per cent. From this analysis Belar derives the 

 formula CuCO,, 3Zn(OH) 2 requiring a ratio of C0 2 : KO : H 2 = 

 1:4:3 while his analysis yields I'll : 4*00 : 3 # 24, an agreement 

 which is not satisfactory as may also be seen by comparing the 

 theoretical composition Y with analysis I. The other analyses 

 are of little value as they do not add up very close to 100 per 

 cent and in II and III the loss on ignition is certainly nearer 

 to the theory for the original formula, VI above, than for 

 Belar's Y. It is possible that Belar's analysis I is correct and 

 that there is a mineral resembling aurichalcite with a definite 

 formula, but if so it must be settled by more exact analyses 

 and be designated as a distinct species. 



An analysis by Berzelius* of an artificial salt, prepared by 

 precipitation from a solution of zinc sulphate with sodium car- 

 bonate in the cold, washing the precipitate and drying to con- 

 stant weight in a vacuum, is of interest here as he derived for 

 it a formula exactly analogous to that of aurichalcite, 2ZnCO s 

 3Zn(OH) 2 . His analysis, together with the theoretical compo- 

 sition are given below. 





C0 2 



H 2 



ZnO 



Berzelius, found.. 



15-939 



10-714 



73-347 = 100-000 



Calculated 



. 16-06 



9-85 



74-09 = 100-00 



In closing the author desires to express his thanks to Prof. 

 E. S. Dana for his kindness in furnishing the material for 

 carrying on this investigation. 



Mineralogical Laboratory, Sheffield Scientific School, 

 New Haven, Nov. 22d, 1890. 



* Berzelius, Jahresbencht, xv, p. 180, 1836. 



