Rate  of  Decay  of  Active  Deposit  from  Radium.        149 
A  large  number  of  experiments  were  made  in  this  manner 
using  temperatures  varying  from  700°  to  1100°  C,  but  in 
no  case  did  the  period  fail  below  twenty-six  minutes. 
If  then,  as  the  above  experiments  seem  to  show,  the  results 
of  Curie  and  Danne  are  to  be  explained  by  the  volatilization 
of  one  or  more  of  the  constituents  of  the  active  deposit,  we 
should  not  expect  to  find  the  period  of  that  part  of  the  active 
matter  remaining  on  the  wire  a  function  merely  of  the  tem- 
perature, for  other  conditions  besides  temperature  ought  to 
affect  the  amount  of  volatilization,  and  this  was  found  to  be 
the  case.  For  example,  the  removal  of  the  volatile  products, 
by  blowing  a  current  of  air  through  the  furnace  or  by 
inserting  a  cold  copper  rod  for  a  few  seconds  before  removing 
the  platinum  wire,  always  diminished  the  period  of  the  matter 
remaining  on  the  wire. 
Fig.  4  is  a  fair  example  of  the  results  obtained  when  the 
active  matter  is  deposited  on  a  platinum  wire  and  heated  in 
the  furnace. 
Ffe.  4. 
1.204 
§  .903 
.ecc 
301 
X 
,/ 
Nrc 
^     \* 
No 
X 
X6^ 
X 
x^ 
X 
\ 
_^     x. 
\  Y 
\\l  \ 
"25 
75  100 
Time  iai  Minutes 
125 
150 
175 
A,  B,  C,  and  G  are  four  decay  curves  of  the  active  deposit, 
which  had  been  previously  heated  to  about  800°  0.  In  the 
case  of  the  other  three  curves,  the  temperature  used  was 
about  900°  C.  The  time  is  reckoned  from  the  removal  of 
the  wire  from  the  emanation.  The  first  points  on  curves  F 
and  G  should  be  at  about  200  and  300  minutes  respectively, 
as  in  these  cases  the  wires  were  not  placed  in  the  furnace  for 
several  hours  after  their  removal  from  the  emanation.  As 
was  expected,  the  period  was  found  to  vary  considerably,  but 
it  was  always  smallest  when  care  was  taken  to  remove  the 
volatile  matter  from  the  furnace  before  removing  the  wire. 
A  large  number  of  other  curves  were  taken  both   at  lower 
