Am.  Jour.  Pharm.  \ 
April,  1909.  j 
A  Piece  of  Pitchblende. 
169 
tempt  has  been  made  to  reduce  radium  to  the  elemental  state ;  there 
can  be  no  doubt,  however,  that  it  would  be  found  to  be  a  metal 
similar  to  barium,  which  it  closely  resembles  in  its  compounds.  The 
chemical  reactions  and  the  spectrum  of  radium  are  analogous  to 
those  of  the  alkaline-earth  metals,  and  its  atomic  weight  of  about 
226  fixes  its  position  as  the  fourth  member  of  this  family  in  the 
periodic  system  of  Mendelejeff.  Small  amounts  of  radium  salts 
have  been  prepared  in  the  pure  state  by  the  Curies,  by  the  German 
chemist  Giesel,  and  quite  recently  by  the  Austrian  Radium  Commis- 
sion. In  appearance  and  reactions  they  differ  very  little  from  the 
corresponding  barium  salts,  but  are  readily  distinguished  from  the 
latter  by  their  radio-activity.  With  the  most  approved  processes  less 
than  fifty  grains  of  radium  bromide  have  been  obtained  from  ten 
tons  of  uranium  residues,  and  the  entire  stock  of  pure  radium 
preparations  now  in  the  hands  of  investigators  probably  falls  short 
of  100  grains.  You  can  readily  appreciate  the  exceedingly  precious 
character  of  this  material. 
In  addition  to  polonium  and  radium  a  number  of  other  radio- 
active bodies  have  been  separated  from  various  uranium  and 
thorium  minerals.  They  differ  from  radium  both  in  their  chemical 
character  and  in  their  radio-active  properties,  but  for  the  most  part 
appear  to  trace  their  origin  to  the  same  parent  substance.  The 
most  interesting  among  them  are  actinium,  which  Debierne  has 
separated  from  the  thorium  contents  of  pitchblende,  and  ionium, 
recently  discovered  by  the  American  chemist  Boltwood,  as  a  con- 
stituent of  carnotite,  a  vanadate  of  uranium  found  in  Colorado. 
The  discovery  of  the  radio-active  substances,  and  especially  of 
radium,  has  had  a  wonderfully  stimulating  influence  on  research  in 
physical  science,  and  the  advances  that  have  been  made  in  this 
field  during  the  past  decade  have  been  so  rapid  that  it  would  lead  us 
far  beyond  the  scope  of  this  lecture  to  consider  even  in  a  general 
way  our  present  knowledge  of  the  subject.  I  must  content  myself 
with  bringing  to  your  attention  a  few  facts  that  will  help  you 
understand  the  role  which  the  radio-active  substances  play  in  pitch- 
blende. 
It  has  been  ascertained  that  the  rays  emitted  by  these  substances 
are  of  three  distinct  types,  differing  from  one  another  in  their  power 
of  penetrating  matter  and  in  their  behavior  towards  the  magnetic  or 
electric  field.  They  are  respectively  known  as  alpha,  beta,  and 
gamma  rays.    The  alpha  rays  are  completely  stopped  by  a  layer  of 
