Am.  Jour.  Pharm. 
April,  1909. 
A  Piece  of  Pitchblende. 
but  it  has  recently  become  the  source  of  that  most  interesting  con- 
stituent of  pitchblende,  radium. 
Let  us  now  return  to  the  question  of  the  chemical  composition  of 
our  mineral.  Can  it  be  expressed  like  that  of  any  well-defined 
species  by  a  definite  formula?  I  know  of  no  other  mineral  that  has 
presented  so  many  difficult  problems  to  the  analyst,  and  of  none  that 
has  so  persistently  defied  his  efforts  to  unravel  its  innermost  nature, 
as  has  uraninite.  An  enormous  number  of  analyses,  and  many  of 
them  by  the  most  skilful  chemists,  have  been  recorded,  but  our 
knowledge  of  the  constitution  of  the  mineral  is  far  from  complete. 
In  one  respect.,  however,  all  analyses  agree :  that  the  principal  con- 
stituent of  pitchblende,  say  from  50  to  80  per  cent,  of  it,  is  the 
uranate  of  uranyl,  or  in  the  shorthand  of  chemists,  Ur3Os.  In 
addition  to  this,  varying  amounts  of  many  other  elements  have  been 
found  in  the  different  varieties ;  indeed  it  would  seem  as  if  nearly 
all  of  the  known  elements  existed  in  one  or  another  of  the  modifica- 
tions of  this  mineral.  That  many  of  the  minor  constituents  are 
merely  admixtures,  that  is  to  say,  do  not  enter  into  the  composition 
of  uraninite,  is  generally  recognized,  but  the  role  which  others  play 
in  it  is  only  imperfectly  understood. 
Invariably  present  in  all  varieties  are  the  oxides  of  lead  and  iron  ; 
the  majority  contain  also  alumina,  lime  and  magnesia,  and  some  of 
the  rarer  varieties  are  characterized  by  considerable  proportions  of 
rare  earths,  such  as  thoria  and  yttria. 
It  is  not  my  intention  here,  to-night,  to  discuss  the  extended 
literature  on  this  subject,  but  I  can  recommend  it  as  affording  much 
interesting  and  some  amusing  reading;  one  writer  after  another 
claims  to  have  solved  the  riddle  of  the  composition,  and  charges  all 
others  with  the  gravest  errors,  only  to  be  told  in  turn  that  he,  too.  is 
entirely  mistaken. 
It  was  on  account  of  an  unfortunate  oversight  in  the  analysis  of 
cleveite  that  one  of  the  foremost  chemical  experts  of  our  country 
just  missed  the  honor  of  having  discovered  that  most  interesting  of 
gaseous  elements,  helium.  This  is  the  way  it  happened  :  In  189 1 
Dr.  Hillebrand,  chief  chemist  of  the  United  States  Geological 
Survey,  observed  that  many  of  the  uranium  minerals,  and  notably 
cleveite,  give  off  considerable  quantities  of  gas  when  they  are  heated 
with  acids.  He  carefully  collected  this  gas  and  subjected  it  to 
various  tests,  but  although  he  noticed  certain  peculiarities  in  its 
behavior,  he  concluded  that  it  was  nitrogen.    Four  years  later  the 
