J*  }  Miscellaneous  Mineralogical  Notes. 
797 
Analysis  of  a  Feldspar  from  Virginia. — 
Per  Cent. 
Si02   
FeX>3  plus  ALO. 
64.69 
19.93 
0.31 
13.32 
2.83 
CaO 
K20 
Na20 
HX> 
none- 
Total 
101.08 
Note. — This  mineral  had  been  ground  and  rendered  anhydrous 
by  gentle  ignition  before  assay. 
Examination  of  a  Nephelite  from  Magnet  Cove,  Arkan- 
sas.— 
Geyser  Incrustation  from  Western  United  States. — This 
incrustration  contained  white  patches  of  potassium  nitrate. 
Spanish  Brown,  Burnt  Umber  and  Burnt  Sienna. — These 
are  ferruginous  earths,  the  iron  being  in  various  stages  of  oxidation 
with  resultant  variation  in  the  colors  of  the  earths.  These  earths 
are  used  to  some  extent  in  pharmaceutical  preparations  for  which 
purpose  freedom  from  arsenic  and  heavy  metals,  other  than  iron,  is 
essential.  Numerous  lots  of  these  earths  were  examined  during  the 
past  few  years  and  in  no  case  were  heavy  metals,  other  than  iron, 
found.  Arsenic  is  frequently  found,  however,  although  not  often 
in  excessive  quantities.  The  arsenic  amounts  as  high  as  1  part  in 
1,000  in  some  specimens.  This  is  excessive.  Only  those  earths  in 
which  the  arsenic  is  present  to  the  extent  of  not  more  than  1  part 
in  50,000  parts  should  be  offered  to  the  pharmaceutical  trade  and 
preferably  the  arsenic  should  not  be  greater  than  1  part  in  100,000 
parts,  which  is  the  amount  permitted  in  medicinal  substances  by  the 
United  States  Pharmacopoeia. 
Analysis  of  a  Tripoli  from  Western  United  States. — This 
tripoli  was  very  white,  friable,  and  easily  reducible  to  an  excellent 
polishing  powder. 
Xa,0 
K.O 
Per  Cent. 
Analysis :  SiO; 
99.14 
0.48 
0.27 
99.89 
Fe2Ori  +  ALO; 
HX>   
Total 
