ADecimber?ito2m'}    Re  cent  Literature  Relating  to  Pharmacy.  607 
which  contain  either  uranium,  yttrium  or  thorium.  It  has  also  been 
found  in  the  gas  emanating  from  several  of  the  European  thermal 
springs  and  has  been  definitely  proven  to  exist  in  liquid  air.  From 
observations  that  have  been  made  it  has  been  determined  that  this 
element  is  one  of  the  constituents  of  our  atmosphere  in  the  ratio  of 
I  or  2  parts  in  a  million.  The  latest  determinations  of  its  density 
appear  to  make  it  about  I  98  and  its  atomic  weight  about  3  96. 
Other  Members  of  the  Group. — Professor  Ramsay,  in  a  lecture 
before  the  Deutsche  Chemische  Gesellschaft  in  December,  1898,  gave 
an  account  of  the  steps  which  led  to  the  discovery  of  the  other 
members  of  the  group. 
The  search  for  these  elements  was  occasioned  by  an  attempt  to 
fit  argon  and  helium  into  the  periodic  system.  If  4  and  40  were 
assumed  to  represent  the  atomic  weights  of  helium  and  argon 
respectively,  there  would  be  a  space  to  be  filled  by  an  element  hav- 
ing an  atomic  weight  about  16  higher  than  helium. 
The  quest,  begun  by  Ramsay  and  Collie  and  continued  by  Ram- 
say and  Travers,  opened  with  a  careful  re-examination  of  the  min- 
erals which  had  proved  to  be  a  source  of  helium.  The  search  was 
later  extended  to  other  minerals  of  different  chemical  character,  but 
with  uniformly  negative  results.  Meteorites  and  the  gases  from 
mineral  springs  were  equally  unproductive. 
Attention  was  then  turned  to  argon,  and  its  study  in  connection 
with  liquid  air.  It  was  pointed  out  that  the  atomic  weight  of  argon 
would  be  more  tractable  if  it  could  be  reduced  to  below  40,  and  a 
search  alter  a  constituent  of  the  air  having  a  lesser  density  than  20 
seemed  worth  the  making. 
In  preparing  to  liquefy  a  quantity  of  purified  argon,  with  the  aid 
of  liquid  air,  it  was  thought  worth  the  while  to  examine  the  last 
fractions  of  some  evaporating  liquid  air.  After  removing  the  oxygen 
and  the  residual  nitrogen,  Ramsay  found  that  there  were  present,  in 
the  spectrum  of  the  residual  gas,  a  number  of  the  new  lines,  notably 
a  yellow  line  not  identical  with  that  of  helium,  and  a  new  green  line. 
The  gas  had  a  density  of  22  5  instead  of  20  and  the  ratio  of  specific 
heats  of  the  mixture  of  gases  was  found  to  closely  approximate 
166.  Here,  then,  was  a  new  element  or  elements,  but  not  the  one 
sought  for.  Ramsay,  assuming  the  presence  of  one  only,  gave  it  the 
name  "  Krypton  "  (the  concealed  one). 
This  gas  has  been  studied  more  closely  since  that  time.    It  is 
