Mineralogy of South America. 135 



that the proprietors and managers of the speculation quite ridi- 

 culed the idea of such being the case. Are we to suppose that 

 some of the Cassiterite may have been reduced and melted by 

 forests on fire, as before hinted as possible although not very 

 probable ? I record the facts here, but must say I am puzzled 

 to come to a definite conclusion ; for the tin itself in no specimen 

 yet observed was associated with a veritable roek matrix. True 

 it is that it was always extremely impure, and contained stony 

 matter throughout its substance, as if entangled in it, as would be 

 expected in case it had been thrown on to the ground when in a 

 fused state ; yet its appearance left the distinct impression on 

 the mind of its having been melted in an ordinary manner. 



The specific gravity taken at 60° F. on 556*8 grs. of the smaller 

 and purest fragments was found to be 7*502, which, being consi- 

 derably higher than pure metallic tin, made a chemical examina- 

 tion of the tin desirable ; and its analysis was conducted as follows. 

 On attempting to dissolve it in nitric acid, I found it so 

 passive, that even several hours' boiling in the acid made no 

 impression whatever on it. I found, however, by heating the 

 tin up to near its melting-point, and allowing it to cool slowly 

 previously to immersion in the acid, that it then was readily 

 acted upon with formation of oxide of tin. 



26*74 grs. thus treated afforded 27*12 of tin along with 

 insoluble residue and arsenic acid, and, deducting these, 26*75 

 binoxide of tin, equal to 21*06 metallic tin, or 78*75 per cent. tin. 

 The nitric-acid solution was, after neutralization with am- 

 monia, treated with hydrosulphate of ammonia, and left sulphide 

 of lead, with a little sulphide of iron and copper, which afforded 

 respectively 7*43 grs. sulphate of lead, equal to 5*46 grs. me- 

 tallic lead, or 20*42 per cent., a trace of copper, and 0*08 gr. 

 sesquioxide of iron, equal to 0*05 iron, or 0*20 per cent. 



Arsenic was determined on a separate portion (24*08 grs.) by 

 dissolving in hydrochloric acid, passing the evolved gas through 

 nitric acid, and determining the arsenic acid as arseniate of 

 ammonia and magnesia, 0*11 gr. being equivalent to 0*04 me- 

 tallic arsenic, or 0*17 per cent. The rocky insoluble matter 

 was also separately determined on a fresh portion of the tin. The 

 results thus obtained, when tabulated, will stand as follows : — 



in 2674. in 100. 



Tin 21*06 78*75 



Lead ....... 5*46 20*42 



Copper trace trace 



Iron 0*05 0*20 



Arsenic 0*04 0*17 



Insoluble gangue . . . 0*30 1*12 



2^91 100*66 



