36 
CONTRIBUTIONS TO MINERALOGY. 
[BULL. 262., 
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 con- 
tains lead in the place, of alkalies. The results by Hillebrand are as 
follows: 
i. 
II. 
III. 
IV. 
Mean. 
Ratio. 
Fe 9 0, 
42.36 
.12 
19. 69 
.17 
&.21 
27. 05 
.02 
9. 59 
.56 
.27 
.05 
.01 
42.38 
.08 
19. 99 
42.37 
.10 
19.84 
. 17 
h . 21 
27. 06 
.02 
9. 54 
.51 
.27 
.05 
.01 
0. 265^ 
3. 15 
.001/ 
.089 1.05 
A1A?«... 
PbO 
K. ( () 
0.11 
19. 89 
19. 79 
Na./) 
SO, 
27. 07 
. 338 4. 00 
II.,() below 105° 
11,0 above 105° 
Si0 2 . 
9.49 
.51 
.27 
. 530 6. 21 
.47 
CuO 
CaO . 
MgO 
100. 15 
"The presence of alumina was not definitely proved. The figures here given are the difference 
between the several weights of the ammonia precipitates and those of the ferric iron in them, a i ( 
determined by permanganate after reduction by hydrogen sulphide. 
£• Probably somewhat high. 
The ratio of Fe 2 :} : PbO : S0 3 : H 2 is very close to 3 : 1 : 4 : 6 
indicating that the mineral is a variety of jarosite, and the sligh 
excess of Fe 2 0. ? , H 2 0, and PbO + alkalies may be accounted for b;i| 
assuming that slight impurities are present, partly ferric hydroxide j 
in part some lead salt, and perhaps a soluble silicate, as shown by th'jl 
complete solubility of the silica in acids. Assuming that the ratio i J 
exactly 3:1:4: 6, it is found that 4.36 per cent of impurities ar > 
present, and the remaining 05.64 per cent may then be regarded ai 
plunibojarosite, as follows: 
Theory for PbFe 6 
[0H] 12 [S0 4 ] 4 . 
Fe 2 3 40. 59 or 42. 44 
PbO 18. 86 or 19. 72 
HX) 9. 13 or 9. 55 
95. 64 or 100. 00 
Since it took probably 2,500,000 crystals of natrojarosite to make 
gram of material, it certainly must have taken fully 4,000,000 to mal* 
a gram of plunibojarosite, for the crystals of the latter miners 
though somewhat heavier, are decidedly thinner than those of tH 
former; hence the presence of 4.5 per cent of impurities in such f| 
crystalline product is not to be wondered at. 
