Am.  Jour.  Pharm.  > 
April,  1909.  | 
A  Piece  of  Pitchblende. 
165 
lines  of  this  spectrum  was,  however,  soon  recognized  by  Sir  Norman 
Lockyer  as  the  yellow  "  D3  "  line  which  he  and  Janssen  had  observed 
in  the  spectrum  of  the  sun's  chromosphere  during  the  eclipse  of  1868. 
The  brilliant  line  had  been  attributed  to  an  element  supposed  to  exist 
only  in  the  sun  and  certain  stars,  and  this  hypothetical  solar  constit- 
uent had  accordingly  been  named  helium  (from  Helios,  the  sun). 
Thus  after  a  lapse  of  27  years  terrestrial  helium  was  found,  and  the 
searching  investigations  of  Prof.  Ramsay  and  of  the  Swedish  chemist 
Langlet  soon  established  the  true  character  of  the  new  element. 
Like  argon,  it  was  found  to  be  devoid  of  chemical  energy,  showing 
no  tendency  to  form  compounds  with  any  of  the  known  elements, 
and  to  consist  of  monatomic  molecules.  Physically,  however,  it  dif- 
fered from  argon  in  its  lightness — its  density  is  only  2  compared 
to  hydrogen — in  its  very  slight  solubility  in  water,  in  its  behavior  at 
low  temperatures,  as  well  as  in  other  ways. 
Of  all  the  gases  known  to  chemistry  helium  is  the  most  perfect. 
Thermometers  filled  with  it  afford  the  most  reliable  means  of 
measuring  extremely  low  temperatures,  and  the  liquefaction  of  this 
gas,  which  was  only  recently  effected  by  Prof.  Kamerlingh  Onnes 
of  Ley  den,  is  regarded  as  the  crowning  triumph  of  low-temperature 
research.  The  picture  and  diagram  upon  the  screen  will  give  you 
an  idea  of  the  complicated  apparatus  by  which  the  Dutch  physicist 
attained  his  object. 
The  occurrence  of  helium  is  by  no  means  confined  to  the  heavenly 
bodies  and  cleveite.  Minute  quantities  of  it  exist  in  the  atmosphere, 
it  is  present  in  the  gases  dissolved  in  many  mineral  waters,  like  those 
of  Bath  and  Cauterets,  and  has  been  detected  in  a  great  number  of 
minerals,  particularly  those  containing  the  heavy  elements  uranium 
and  thorium. 
In  view  of  the  circumstances  surrounding  the  discovery  and 
investigation  of  helium,  you  will  readily  appreciate  the  prominent 
part  this  element  has  played  in  the  recent  history  of  chemistry;  yet 
its  claims  upon  the  attention  of  scientists  were  to  be  vastly  enhanced 
by  another  discover}'  for  which  pitchblende  also  supplied  the 
material. 
This  brings  us  to  the  most  interesting  chapter  of  our  story.  In 
1896  the  late  and  lamented  Henri  Becquerel,  while  engaged  in  the 
study  of  the  phosphorescence  of  certain  uranium  salts,  made  the 
remarkable  observation  that  they  continuously  emit  rays  of  a  peculiar 
character.    His  experiments  showed  that  these  radiations  could  not 
