Am.  Jour.  Pharrn.") 
April,  1909.  J 
A  Piece  of  Pitchblende. 
161 
The  external  characters  of  uraninite  from  different  localities  vary 
within  wider  limits  than  those  of  other  species.  In  rather  rare  in- 
stances the  mineral  is  crystallized  in  cubes  or  octohedra,  but  usually 
it  is  massive  or  of  granular  structure.  Its  color  is  grayish,  greenish- 
brown,  or  black  ;  its  lustre  pitch-like  or  dull.  The  specific  gravity 
fluctuates  from  6.5  to  nearly  to. 
Martin  Heitirich  Klaproth 
Now  a  substance  which  exhibits  such  great  variations  in  its 
physical  properties  must  also  be  variable  in  its  chemical  composition, 
and  pitchblende,  as  we  shall  see,  is  no  exception  to  this  rule.  The 
chemical  history  of  the  mineral  began  in  1789,  when  a  German 
apothecary,  Martin  Henry  Klaproth  by  name,  discovered  that  its 
principal  constituent  was  a  previously  unknown  metal  to  which  he 
