512  Melting  Points  and  Solubility  of  Salts.        {Xm~  iTisu*™' 
NOTE  ON  THE  MELTING  POINTS,  AND  THEIR  RELA- 
TION TO  THE  SOLUBILITY  OE  HYDRA  TED  SALTS. 
By  William  A.  Tilden,  D.Sc,  F.R.S. 
In  a  paper  read  before  the  Royal  Society  last  June,  and  since 
printed  in  the  Philosophical  Transactions,  Mr.  Shenstone  and  I  drew 
attention  to  the  relation  observable  in  the  solubility  of  salts  in  water 
at  temperatures  above  100°,  and  the  melting  points  of  the  same  salts 
in  the  anhydrous  state.  This  relation  may  be  exhibited  by  represent- 
ing the  solubilities  graphically  in  the  usual  manner,  when  it  is  noticed 
that  the  curves  of  solubility  of  the  most  fusible  turn  up  most  rapidly, 
whilst  the  solubility  of  those  less  fusible  increases  nearly  in  propor- 
tion to  the  temperature,  and  the  curves  therefore  approach  a  straight 
line.  This  is  well  seen  in  the  case  of  two  such  salts  as  potassium 
chloride  and  potassium  chlorate,  or  sodium  chloride  and  potassium 
nitrate. 
Feeling  satisfied  that  the  connection  between  fusibility  and  solu- 
bility observed  in  the  salts  referred  to  would  be  found  to  exist  in  other 
cases,  I  have  lately  been  inquiring  into  the  points  of  fusion  of  hydrated 
salts  and  their  solubility  below  these  temperatures.  Very  few  of  the 
melting  points  of  salts  containing  water  of  crystallization  could  be 
found  recorded,  and  I  have  therefore  had  to  make  a  number  of  expe- 
riments. For  assistance  in  this,  and  in  the  determination  of  solubility 
in  a  few  cases,  I  am  indebted  to  Mr.  George  Lloyd,  lately  a  student 
in  the  Mason  College  Laboratory. 
The  melting  points  were  ascertained  in  the  following  manner : 
Near  to  one  end  of  a  piece  of  tubing,  drawn  out  very  thin,  and  about 
a  millimeter  in  diameter,  a  narrow  strip  of  moist  filter-paper  was 
introduced,  and  the  end  then  sealed.  The  tube  was  then  bent  twice 
at  right  angles,  and  into  the  upright  open  end  was  droppd  a  small 
clear  crystal  or  fragment  of  the  crystal  of  the  salt,  and  the  tube  was 
then  attached  to  a  thermometer.  Some  preliminary  trials  having 
indicated  the  melting  point  of  the  salt  within  a  few  degrees,  the  ther- 
mometer and  tube  were  stirred  round  in  water  or  sulphuric  acid  a 
little  below  that  temperature,  and  contained  in  a  beaker  placed  over  a 
lamp.  The  object  of  the  damp  paper  at  the  bottom  of  the  tube  is  to 
supply  water-vapor,  and  so  diminish  the  tendency  of  the  salt  to 
effloresce. 
In  many  cases  the  melting  point  can  be  thus  determined  within 
half  a  degree,  but  though  several  experiments  were  made  in  each  case, 
