Tra7ts. N. V. Ac. Set. 34 Nov. 13, 



Other experiments and analyses were made, and the basis of calcula- 

 tion changed by allowing 75 per cent, of the silica found in solution for 

 the Willemite. The red oxide might also be slightly raised by adding 

 some of the manganese found in solution, the amount to be added 

 being calculated by comparison with the analysis of Zincite already 

 given. Rhodonite has been taken as the silicate of manganese found 

 in these ores, instead of Tephroite, although the latter occurs to some 

 extent — the ratio of occurrence of the Willemite and Rhodonite as- 

 sumed, i.e., I to I, being thought to more than compensate for any 

 silicate of manganese which might go into solution from the presence 

 ot Tephroite. This mineral is somewhat more soluble in acetic acid 

 than Rhodonite, and some allowance should, therefore be made for its 

 possible occurrence. 



The foregoing method, owing to slight variations in solubility, may 

 not be accepted as an exact analytical process, but it undoubtedly gives, 

 within close limits, the red oxide of zinc in the sample treated, pro- 

 vided that proper care be taken in the analysis that the ore is not too 

 finely pulverized, and that the treatment with acid is stopped at the point 

 where the last trace of red disappears. 



Of course, if this latter be continued beyond this point, or the ore be 

 too fine, more silicates will be dissolved than is absolutely necessary, 

 and the error in calculating will be increased, the results being propor- 

 tionally incorrect. 



DISCUSSION. 



Mr. A. H. Elliott enquired concerning the condition in which 

 the copper probably existed. 



Mr. N. H. Darton stated his observation of the occurrence of sili- 

 cate of copper at Franklin ; and that Dr. Hayes had established by 

 microscopic examination that the color of red oxide of zinc was due 

 entirely to disseminated scales of specular oxide of iron. 



Mr. JULIEN remarked on the importance of the discovery of the 

 complete solubility of the red oxide of zinc in acetic acid. The purity 

 of the minerals used in the analyses might have been ensured by 

 previous microscopic examination, all but the Franklinite being trans- 

 lucent in thin section. The variation in the recorded analyses of 

 Willemite, etc., may be largely due to the absence of this precaution. 

 The proportion of the minerals present in the ore might have been as- 

 certained in the fine powder, by microscopic examination. It was a 

 question whether both the alumina and oxide of copper may not have 

 existed in replacement of oxides of iron and zinc. Dependence upon 

 the inexactly defined ratio of solubilities seemed of doubtful value for 

 the determination of the proportion of Willemite and Rhodonite, the 



