Ahinite-Jarosite Group of Minerals. 



215 



The analysis of the mineral was made on the very best 

 material, having a specific gravity of 3*665 at 30° C. The 

 results are surprising, and were wholly unlooked for, since it is 

 found that this jarosite contains lead in the place of alkalies. 

 The results by Hillebrand are as follows : 





I. 



• II. 



III. 



Fe . - . 



42-36 



42-38 



•08 

 19-99 





Al ?* 



•12 



•11 



PbO 



19-69 



19^89 



K 



•IT 





NaO 



.... -211 





SO3 



27-05 



27-07 





H,0 below 



105° ^02 







H^ above 



105° 9-59 



9-49 





SiO, 



•se 



•51 



•47 



CuO 



•27 



•27 





CaO 



Mo^O 



-05 



•Ol 







IV. 



19^ 



Mean. 



42 



19 



'37 



•10 



•84 



•17 



•2 If 



•06 



•02 



•54 



•51 



•27 



•05 



•01 



Eatio. 

 0^265 

 0^001 

 0-089 



V 



15 



1-05 



0-338 4-00 



0^530 6^27 



100^15 



The ratio of Fe,03 : PbO : SO3 : H,0 is very close to 3 : 1 : 4 : 6, 

 indicating that the mineral is a variety of jarosite, and the slight 

 excess of Fe^Oj, HjO, and PbO 4- alkalies, may be accounted 

 for by assuming that slight impurities are present, partly 

 ferric hydroxide, in part some lead salt, and perhaps a soluble 

 silicate, as shown by the complete solubility of the silica in 

 acids. Assuming that the ratio is exactly 3 : 1 : 4: : 6, it is found 

 that 4^36 per cent of impurities are present, and the remaining 

 95*64: per cent may then be regarded as plumbo jarosite, as 

 follows : 



Fe.Og 40^59 



PbO 18-86 



SO3 27^06 



HO 9^13 



Theory for PbFeeCOHJisLSOiJ*. 



or 42^44 



" 19^72 



'' 28^29 



9^55 



95^64 



100-00 



Since it took probably 2,500,000 crystals of natrojarosite to 

 make one gram of material, it certainly must have taken fully 

 4,000,000 to make a gram of plumbojarosite, for the crystals of 

 the latter mineral, though somewhat heavier, are decidedly 

 thinner than those of the former ; hence the presence of 4^5 



"^The presence of alumina was not definitely proved. The figures here 

 given are the differences between the several weights of the ammonia pre- 

 cipitates and those of the ferric iron in them, as determined by permanganate 

 after reduction by hydrogen sulphide. 



\ Probably somewhat high. 



