Am*Mayr.'i903arm'}     Recent  Literature  Relating  to  Pharmacy.  229 
similar  to  those  exhibited  by  uranium.  Thorium  rays  were  first 
observed  by  C.  G.  Schmidt  in  1898.  An  interesting  observation  in 
this  connection  has  recently  been  made  by  Rutherford  and  Soddy. 
They  found  that  when  thorium  hydrate  was  precipitated  from  a  solu- 
tion of  a  thorium  salt  by  means  of  ammonia,  the  resulting  thorium 
hydrate  possessed  little  or  no  radioactivity,  while  the  solution  con- 
tained a  substance  that  has  as  yet  not  been  identified,  which  was 
radioactive.  The  most  interesting  and  surprising  observation,  how- 
ever, was  that  after  several  days  the  precipitated  thorium  hydrate 
had  regained  its  radioactivity,  while  the  substance  soluble  in  the 
ammonia  solution  lost  correspondingly.  The  same  experiment  could 
be  repeated  a  number  of  times  with  the  same  substance. 
Actinium. — This  is  a  name  given  to  a  substance  that  was  separated 
by  Debierne  from  pitchblende.  Actinium  has  some  properties  in 
common  with  thorium,  but  is  said  to  be  5,000  times  as  radioactive. 
It  has  been  questioned  whether  the  radioactivity  of  this  substance 
is  inherent,  or  simply  induced  by  other  more  active  materials. 
Induced  Radioactivity . — Both  radium  as  well  as  thorium,  as  has 
been  pointed  out,  have  the  property  ot  inducing  radioactivity  in 
substances  with  which  they  come  in  contact.  Radium  is  the  more 
active  in  this  respect,  imparting  activity  to  all  materials  with  which 
it  comes  in  contact.  The  intensity  of  the  radioactivity,  induced  in 
other  substances,  depends  on  the  intimacy  of  the  contact ;  if,  for 
instance,  a  salt  is  precipitated  out  of  a  solution  containing  a  radio- 
active chemical,  the  precipitated  salt  will  be  strongly  radioactive  for 
the  time  being,  but  will  gradually  lose  this  property.  As  in  the 
case  of  the  precipitated  thorium  hydrate  the  radioactive  chemical 
loses  a  larger  part  of  its  radioactivity  for  the  time  being,  but  will- 
regain  it  again  on  standing. 
Among  other  substances  that  appear  to  have  radioactive  proper- 
ties it  might  be  added  that  Hoffman  and  Strauss  have  separated  a 
radioactive  lead  from  a  number  of  uranium-bearing  minerals. 
Baskerville  has  separated  radioactive  carolinium  from  thorium;  both 
of  these  substances  are  supposed  to  be  self-radioactive,  and  not 
dependent  on  induction  or  contamination  by  other  more  radioactive 
materials. 
What  the  future  may  have  in  store  is  difficult  indeed  to  say ;  but 
even  from  the  material  to  hand  at  the  present  time,  it  would  appear 
that  physicists  and  chemists  have  before  them  a  problem  that  will 
