400 F. A. Genth — Contributions to Mineralogy, 



fine enough to pass through a sieve of about fifty meshes to 

 the inch, and separated by Thoulet's solution \ afterwards the 

 magnetite was taken out by a magnet and the resulting ma- 

 terial, apparently pure, was analyzed. To my great surprise 

 considerable quantities of phosphoric acid were found which 

 was present as apatite, which by a closer microscopic examina- 

 tion of the original specimens could easily be distinguished. 

 The analyses gave : 



Ignition = 



Si0 2 



Al 2 O s 



MnO 



FeO 



MgO 



CaO 



PA 



99-98 99*91 



Deducting the phosphoric acid as Ca 5 F(P0 4 ) 3 (flu or apatite) 

 in the first analysis 4*57 per cent, in the second 4'82 per cent 

 of the same, gives the following as the composition of the pure 

 Arkansas Monticellite : 



1. 



2. 



2*28 



2-29 



33-47 



33-46 



0-16 



0-19 



1-11 



1-13 



5-09 



4-93 



20-71 



20-52 



35-18 



35-31 



1-98 



2-08 





l. 



Mol. ratio. 



Ignition 



= 2-39 



•133 



Si0 2 



35-08 



•585 



A1 23 



0-17 



___ 



MnO 



1-16 



•016 ) 



' -074 \ 



•543 ) 



FeO 



5-33 



MgO 



21-71 



CaO 



34-16 



•610 



2. 



Mol. ratio. 



2-41 



•133 



35-19 



•586 



0'20 







1-19 



•016 1 



5-18 



•072 [ 



21-58 



•540 ) 



34-25 



•611 



■633 5-18 -072 V *628 



100-00 100-00 



Leaving out the water, the molecular ratios of Si0 2 : (Mg,Mn, 

 Fe)0 : CaO are : 



in 1, -585 : '633 : -610 



in 2, -586 : -628 : -611 



corresponding to* (Mg,Mn,Fe) 2 SiO . Ca 2 Si0 4 . 



In both analyses the Si0 2 is a little short. As there is no 

 sign of alteration and no lack of basic oxides, it is difficult to 

 account for the presence of over 2 per cent of water, as the 

 finely powdered mineral had been kept over sulphuric acid for 

 several days before analyzing. 



Chemical Laboratory, 111 S. 10th St., Philadelphia, Feb. 1, 1891. 



