502     Prof.  Wilson  and  Mr.  Gold  :  Electrical  Conductivity  of 
compared  with  that  of  the  negative  ions,  the  arrangement 
will  behave  like  a  condenser  if  the  number  of  ions  per  c.c.  is 
very  large  and  the  mass  of  the  negative  ions  very  small. 
Denoting  the  apparent   capacity  per  unit  area  by  C,  we 
have  C=V8^T4§>' 
where  K  is  the  apparent  specific  inductive  capacity.  Con- 
sequently p  =  a°-|y     The  length  of  the  spark-gap  used  in 
the  experiments  on  the  variation  of  the  apparent  capacity 
with  the  concentration  and  nature  of  the  salt  was  about 
2  mms.  in  hydrogen  gas  at  atmospheric  pressure.  The 
Tesla  coil  had  33  turns  in  its  primary  coil  and  3  turns  in 
its  secondary,  so  that  V0  was  about  400  volts  or  1'2  E.S. 
units.  D  was  0*6  cms.,  so  that  for  the  strongest  K2C03 
solution  sprayed,  for  which  K  =  100  (p.  496),  we  have 
1-2  x  10000 
2x3-lx0'62 
The  charge  on  one  ion  is  3  x  10-10  E.S.  units,  so  that  the 
number  of  ions  per  c.c.  was 
5400         18x10- 
p  =  —  ^  =  5400  E.S.  units. 
3  x  10- 
10 
The  amount  of  salt  entering  the  flame  was  determined  by 
finding  the  loss  of  weight  of  a  bead  of  sodium-chloride  placed 
in  an  equal  Bunsen  flame,  so  that  the  light  emitted  by  this 
flame  was  equal  to  that  emitted  by  the  flame  when  a  solution 
of  NaOl  containing  10  grains  per  litre  was  sprayed.  In  this 
way  it  was  found  that  0'53  milligram  entered  the  flame 
per  minute.  Consequently  the  amount  of  K2C03  entering 
the  flame  per  minute  with  the  strongest  solution  was  5*3  milli- 
grams. The  velocity  of  the  flame-gases  was  about  200  cms. 
per  second,  and  the  diameter  of  the  flame  about  3  cms.,  so 
that  the  amount  of  salt  per  c.c.  in  the  flame  was  about 
—7: ,i  erw    V»7\  =  7  x  10  ~5  milligram. 
200x7r(l'0)2xb0  ° 
Hence,,  taking  the  mass  of  an  atom  of  hydrogen  as  10"2* 
gram,  the  number  of  salt  molecules  per  c.c.  was  about 
7  x  IP"8      _  14 
138xlO-^-°XiU   * 
It  thus  appears  that  about  one  molecule  in  30  molecules  of 
K2C03  was  ionized  in  the  flame.     For  most  of  the  other  salt 
solutions  sprayed  the  proportion   of  the  molecules  ionized  in 
the  flame  comes  out  less  than  one  in  30. 
