212 Hunt and Krcms — Composition of Melanochalcite. 



porcelain boat. Copper was precipitated as CuCnS, ignited. to 

 constant weight, and weighed as CuO. Iron was titrated, and 

 zinc thrown down in a neutral solution as the phosphate. 



A chemical analysis following the methods outlined above 

 gave the results indicated in column 2. In column 1 will be 

 found the analysis of Koenig's material, which is here included 

 for comparison. 



1 2 



Koenig Hunt 



CuO 76-88 88-94 



SiO a 7-80 4-31 



C0 2 7-17 1-78 



H 2 7-71 4-48 



ZriO „ 0-41 0-12 



Fe„0„ 0-07 0-22 



100-04 99-85 



While Koenig admitted the possibility of several interpreta- 

 tions of his analysis, he was inclined to believe that the mineral 

 should be considered a basic salt of the very unusual ortho- 

 silico-carbonic acid H 4 (Si,C)0 4 .H„0, in which Si and C replace 

 each other within certain limits. By replacing the hydrogen 

 wholly by Cu and the H„G partly by CuO, the formula for 

 melanochalcite, according to Koenig, becomes Cu„(Si,C)0 4 .Cu 

 (OH).,. However, the analysis given in column 2 contains too 

 much CuO and is likewise too low in SiO„, C0 2 and H 2 to 

 permit of such an explanation. Moreover, both analyses lend 

 to a much simpler interpretation without calling upon the 

 presence of a complex acid whose existence is doubtful. If 

 ZnO is considered isomorphous with CuO and the small 

 amount of iron is neglected, both analyses can be interpreted 

 as mixtures of malachite, chrysocolla and tenorite, as may be 

 seen from the accompanying tables : 



Excess 



0-0071 







Table 1. 









Koenig's 



Analysis 







Molecular ratios 



Malachite 



Chrysocolla 



Tenorite 



CuO. 



0-96583 ) 



0-32590 



0-12914 



0-51585 



ZnO. 



0-00506 ) 









co„. 



0-16295 



0-16295 







HO 



0-42833 



0-16295 



0-25828 





SiO . 



0-12914 





0-12914 







0-65180 



0-51656 



0-51585, or 







5-044 



4-000 



3-992 



