426 OBSERVATIONS IN CHEMISTRY AND MINERALOGY, 



Formula is (Na, K) 2 S0 4 . (Fe^SO^s) . (HO) 12 + basic ferrisulfate 

 (Fe 2 3 )o.57(S0 3 )o. 2 6(H 2 0) 1 .3. 





9. On Mimetitb from Santa Eulalia. 



This is the companion of the natro j arosite at Santa Eulalia. It occurs ' 

 small six-sided prisms with pyramidal poles. The faces are uneven* the onln 



m + -1-1 J ** vy\JIUr 



is honey-yellow. 



The following analysis was made under my direction by Mr. Dan Newkirk 

 an advanced student. The material had been carefully picked over. 2800 

 gram gave: 0.0285AgCl = 2.51 per cent CI; 0.2717PbSO 4 = 70.0 percent Pb« 

 0.0855Mg 2 As 2 O 7 = 22.60 per cent As 2 5 . 2.51 per cent of CI require 7.3 per 

 centPb to form PbCl 2 ; hence 70.0 - 7.3 = 62.7 per cent Pb must be PbO = 67.6 

 per cent. Therefore the composition of mineral is 



PbO = 67.6 : 223 = 0.3031 

 As 2 O fi = 22.6 : 230 = 0.1000 

 PbCl 2 - 9.8 : 278 = 0.0352 



100.0 



Hence 3.03PbO . As 2 6 -f- 0.35PbCl 2 or 3 . (Pb 3 (As 2 4 ) 2 ) . PbCl 2 + 0.09PbO 

 The summing up of the results to an exact 100 must be ascribed to accident 

 Lead is slightly in excess, namely 0.67 per cent. 



EXPLANATION OF PLATE XXXVI 



Fig. 1. Simple microscopic crystals of praseooctaminosulfate. Forms a, b, c show normal develop- 

 ment; d shows tabular development parallel to clinopinakoid; the positive and negative hemidomes and 

 orthopinakoid produce the pseudohexagonal outline; e is a partly developed form; / a combination of forms; 

 d and h the so-called paddle form ; h the staff-type overwhelmingly prismatic ; g the book-type. 



Fig. 2. Bizarre twin forms: a, nearly rectangular twin producing the block-type; b, the butterfly type; 

 c, the bug type ; d, the tongs type ; c, /, g, incomplete twins. 



Fig. 3. a, b, the chi or saw-buck type; c, the angle-templet type; ff, the tongs type; d, the burr-type; 

 e, the digitate-type; h, g, the grass-type. 



Fig. 4. Microscopic figure prepared from Mohawkite. a u a if o», a*, a«, at, at are blue, monoclinic 

 binations of cupritetraminosulfate; b, b u bt, b t , green, isometric combinations of nicolotetramino chlorid; 

 cccc . . ., olive-green monoclinic combinations of praseo-cobaltioctaminosulfate. 



Fig. 5. Glass-tube with a fascicle a of copper wire tied by two asbestos cords, b, c; in sectional view. 



Fig. 6. The glass-tube after the action, a b are the blank spaces which had been protected by the 

 asbestos. Between these two the glass is deeply stained with the ruby color, forward of a less deeply and 

 rearward of b least stained. 



Fig. 7. The mixed effect of ruby stain and superficially attached nnnnor-snanerles. The dots, repre- 



•)•• 



gles are not of the same color in reality, the spangles are of the faint pink 



Kg. 5. Exp 



Fig. 8. Faint and partial staining as produced in Exp. XI. , it 



Fig. 9. Wire-fascicle in outline. Very broad blank rings where protected by asbestos cords, ai 

 a strong ruby stain projecting forward of wires, at ruby stain-band less strongly marked, at c a faint ma 

 of copper-spangles. Exp. XIV. , , ^ 



Fig. 10. Magnificent development of ruby stain between the cords, a faint stain forward of ■» 

 two rings of spangles rearward of b. Exp. XXIII. . . , . . „,,,,- 



Fig. 11. Result of Exp. XXXVI. a, a purple colored ring surrounded by ruby stain; 6, blanK ga» 

 protected by asbestos; c uniformly mixed ruby stain and spangle-copper; d, blank glass; e, mixture 01 hj ^ 

 stain and spangles; /, very dark ruby stain surrounded by aureole; g, blank glass; h, a gray nng; *, » P* 

 gray ring ; k, a bright yellow ring not given in color. 



"» 



«* 



