224 Pirsson and Wells — Occurrence of Leadhillite. 



what doubtful. The earlier investigators, including such emi- 

 nent chemists as Berzlius and Stromeyer, failed to take into 

 account the small amount of water in the mineral, so that its 

 composition was incorrectly supposed to be represented by the 

 formula, PbS0 4 . 3PbC0 3 .' 



Laspeyres, in 1872, described " maxite " as a new mineral, 

 which, while resembling leadhillite in other respects, was 

 hydrous. The question of the identity of maxite and lead- 

 hillite was for some time the subject of a considerable amount 

 of controversy,* but it was satisfactorily shown by Hintzef 

 that leadhillite was also hydrous and that there was therefore 

 no ground for considering maxite as a separate species, and 

 this was finally admitted bj Laspeyres. ;{; 



The formula given to maxite by Laspeyres was, 18PbO . 

 9C0 2 . 5S0 3 . 5H 2 0. Hintze's formula for leadhillite as well 

 as maxite was, 7PbO . 4C0 2 . . 2SO s . 2H 2 0. A simpler and 

 more rational formula has been recently suggested by Groth.§ 

 4PbO . 2CO„ . S0 2 . H„0. The calculated compositions and 

 the molecular ratios for the three formulas are as follows : 



Laspeyres. Hintze. Groth. 



18Pb0.9C0 2 .5S0 3 .5H 2 0. 7PbO . 4C0 2 . 2S0 3 . 2H = 0. 4PbO . 2C0 2 . S0 3 . H 2 0. 

 H 2 1-84 1-86 1-69 



S0 3 8-16 8-27 7-53 



(XX 8-08 9-11 8-29 



PbO 81-92 80-76 82-49 



PbO : COo : S0 3 : H 2 0. 



Laspeyres, 3f If 1 1 



Hintze, 3^ 2 1 1 



Groth, 4^ 2 1 J 



A comparison of the above shows that the differences are 

 not large, and it is evident that slightly impure material or 

 small analytical errors would account for the variations from 

 Groth's simple formula. It is to be noticed also that the deter- 

 minations of S0 3 , made in leadhillite before it was known to 

 be hydrous, agree much more closely with Groth's formula 

 than with the other two. A list of these as cited by Hintze is 

 as follows : 



S0 3 



Berzelius 7 - 58 



Stromeyer 7*21 



Thomson 7*24 



Irving 7*66 



Berlrancl - - . 7*14 



* Laspeyres, Jb. Min., 1872, 407, 508; 1873, 292; J. pr. Ch., N. F., v. 470; 

 vii, 127 ; xiii, 370 ; Bertrand, Bull. Soc. Chim., xix, 17 ; C. R. Ixxxvi, 348 ; Hintze, 

 Pogg. Ann., clii, 256. 



f Loc. cit. % Zeitschr. Kryst., 1877, 193. 



§Tabell. Uebersicht. Min., 1889, p. 62. 



