1889.] NATURAL SCIENCES OF PHILADELPHIA. 47 



0. 0159 up to 360° C. 

 . 0240 up to beginning red-heat ; the color of the powder remains 



unchanged up to this point. 

 . 0290 the powder becomes partly red. 

 0. 0300 at full reddieat. The powder is light brick-red. 

 These numbers furnished : 

 As 2 O 5 = 43.60 

 S6 2 O 5 = 0.25 

 P 2 5 = 0.14 

 Fe 2 O 3 = 30.53 

 Ca O =14.82 

 H 2 O = 9.83 



99.17 

 From this follows the ratio : 



As 2 O 5 : Fe 2 O 3 : Ca : H 2 O. 

 I: 1.09: 1.49: 3.09. 



or very nearly 



in 



Ca 3 Fe 2 [As 4 J 4 [Fe O. H O] 2 -- 5 H 2 O. 



In view of the fact that the color remains unchanged up to red 

 heat and then turns brick-red, the assumption of one molecule of 

 ferric hydrate is well justified as is likewise the consideration of the 

 remaining water as not being constitutional. 



If we compare this composition with that of Arseniosiderite 

 (Rammelsberg, Mineralchemie, Aufl. II, p. 347), we find a close 

 affinity between the two substances. It may hereafter be shown 

 that the composition of the doubtful mineral from Romaneche is 

 identical with the Mazapilite, but for the present it seems proper to 

 distinguish the latter as a perfectly well-established species. 



The mineral Mazapilite occurs at the Mine Jesus Maria, District 

 of Mazapil, Zacatecas, Mex. It was brought thence by Dr. A. E. 

 Foote, to whose kindness the author is indebted for the material. 



March 12. 



The President, Dr. Jos. Leidy, in the chair. 



Eighteen persons present. 



A paper entitled " The Boring Sponge, Cliona ", by Jos. Leidy, 

 M. D., was presented for publication. 



The death of Isaiah V. Williamson, a member, was announced. 



