■Genth.] '^^ [March 18, 



The analysis of the heavier portion of the ore from the San Antonio 

 mine shows 3.86 per cent of dioxide of tin which went into solution by 

 treating the same with chlorliydric acid. As cassiterite is not acted upon 

 by acids, it is difficult to perceive in which form this tin existed. Dissolv- 

 ing in the presence of a neutral solution of auric chloride gave not a trace 

 of reduced gold, therefore neither tin nor arsenic were in the form of the 

 lower oxides. 



There is a sufficient amount of arsenic pentoxide present to combine 

 with all the bases ; the lead is evidently in the form of mimetite of which 

 the calculated percentage would be 13.58 per cent, the zinc is probably 

 there as adamite, and the amount of zinc oxide found would give 6.96 per 

 cent of this mineral ; noarsenateof bismuth has yet been distinguished as a 

 mineral, but there can be no doubt that the bismuth in the San Antonio 

 ore is present as Bi^Og, AsjOj, H2O, the salt which Salkowski has first de- 

 scribed and analyzed (Journ. fiir Praktische Chemie, 104, p. 172), the bis- 

 muth oxide found would give 7.94 per cent of the hydrous arsenate. 



The insoluble portion of the San Antonio ore contains 19.300 per cent 

 of SnO^ and 1.844 per cent of arsenic pentoxide. The atomic ratio be- 

 tween these would be = 16 : 1. To this I shall refer again further on. 



The different varieties of cassiterite show a considerable variation in 

 their speciflc gravity which, in part, is probably owing to cavities pro- 

 duced in the process of their formation. The arsenical varieties have all 

 a lower specific gravity. 



The analyses show that the red varieties are dioxide of tin, contaminated 

 with ferric oxide, and only exceptionally containing an appreciable quan- 

 tity of arsenic pentoxide, while the yellow varieties contain very little 

 ferric oxide, but a far higher percentage of arsenic pentoxide and also in- 

 variably an admixture of zinc oxide. 



It is difficult to perceive how these c(mstituents in such variable quan- 

 tities could be present in apparently perfectly pure and often highly crys- 

 talline minerals. 



Excepting analysis V, in which the ferric oxide is double the amount of 

 the average of the other analyses of the red varieties, which may be 

 owing to the fact that the little crystals of hematite which have been 

 observed being only slightly magnetic, were not completely separated by the 

 magnet, they give the atomic ratio between Fefi^ : SnO.^ = 1:9 and 1 : 

 12. Although the ferric oxide cannot be extracted from the stannic oxide 

 by chlorliydric acid, I cannot favor the idea of a definite compound ex- 

 isting between these oxides, and consider them only as mechanical mix- 

 tures. The high percentage of arsenic pentoxide, especially in the appa- 

 rently purest and highly crystalline globular variety from Mina Varosa, 

 and the constant presence of zinc oxide are very surprising. It suggests 

 the idea that there might be a zi)ic salt of one of the complex inorganic 

 acids consisting of tin dioxide with arsenic pentoxide. A calculation of 

 the molecular ratios of these constituents gave for : 



