290  Rise  of  Salt  Solutions  in  Bibulous  Paper.  {^■ju°ner;Sarm* 
purpose  consists  of  a  glass  tube,  in  which  six  cylindrical  rolls  of 
bibulous  paper  are  placed  end  to  end,  so  that  they  are  in  close 
contact  with  the  walls  of  the  tube  and  with  one  another ;  the  end 
of  the  tube  is  then  dipped  into  the  solution  to  be  examined,  and 
kept  vertically  in  this  position  at  the  ordinary  temperature  until  the 
fifth  roll  is  thoroughly  moistened,  which  is  usually  the  case  at  the 
end  of  three  or  four  days'  time.  The  glass  tube  is  then  broken  at 
the  points  where  the  rolls  touch  one  another,  the  papers  separately 
extracted  with  water,  and  the  solutions  examined. 
Employing  a  solution  of  sodium  chloride  (10  grams)  and  barium 
chloride  (10  grams)  in  100  cc.  of  water,  the  proportion  of  the  former 
to  the  latter  expressed  in  grams  was  found  to  be  1-022,  1-230  and 
1-364  in  the  rolls  I,  3  and  5  respectively,  showing  that  the  more 
diffusible  sodium  salt  rises  more  rapidly  than  the  barium  salt. 
With  a  solution  of  crystalline  ferrous  ammonium  sulphate  (10 
grams)  in  ioo  cc.  of  water,  the  proportion  of  iron  to  ammonia  in 
the  fourth  roll  was  found  to  be  1  :  1-686  when  the  proportion  in  the 
double  salt  is  taken  as  I  :  1  ;  with  a  cold  saturated  solution  of  the 
same  salt,  the  proportion  in  the  fourth  roll  was  I  :  1-004;  and  m 
the  fifth,  I  :  0-993.  Similar  results  were  obtained  with  solutions  of 
ferrous  potassium  sulphate  and  nickel  potassium  sulphate ;  the 
dilute  solutions  showed  a  considerable  amount  of  dissociation, 
whereas  in  saturated  solutions  the  dissociation  was  inappreciable. 
Further  experiments  carried  out  in  a  similar  manner  showed  that 
the  double  salts  formed  by  mercuric  chloride  with  the  chlorides  of 
sodium  and  lithium  are  decomposed  by  water,  but  not  by  alcohol ; 
mercuric  ammonium  chloride,  however,  is  not  decomposed  by  either 
solvent. 
The  following  double  salts,  NaH(NH4)P04  +  4H20 ;  KCN, 
AgCN ;  KNaC4H406  -f  4H20,  do  not  undergo  dissociation  in 
aqueous  solution  ;  the  compound  of  dextrose  with  sodium  chloride, 
2C6H12Oe  -f-  NaCl,  on  the  other  hand,  is  partially  separated  into  its 
components. 
From  experiments  with  solutions  of  naphthalene  picrate,  and  of 
methylindole  picrate  in  acetone  and  in  alcohol,  it  would  seem  that 
no  decomposition  takes  place. 
The  diffusion  phenomena  of  ferrous  ammonium  sulphate,  of  the 
compound  2C6H1206  -f-  NaCl,  and  of  mercuric  sodium  chloride  were 
also  examined  with  the  aid  of  Riidorff's  apparatus  ;  it  was  found 
