184 
Melting  Point  of  Rosin. 
Am.  Jour.  Pharm. 
March,  1919. 
The  first  three  methods  were  carried  out  as  follows :  Glass  tubes 
of  about  i3¥  in.  inside  diameter  and  2  in.  long  were  prepared.  These 
were  dipped  in  melted  rosin  so  that  on  cooling  there  was  left  inside 
the  tube  a  column  of  rosin  of  the  required  depth.  In  the  case  of  the 
method  marked  "film"  the  foot  of  the  glass  tube  was  heated  slightly 
and  applied  carefully  to  the  surface  of  the  molten  rosin  so  that  upon 
cooling  a  thin  film  only  of  the  rosin  was  formed.  The  tubes  were 
attached  to  the  thermometer  in  such  a  way  that  the  bottom  of  the 
tube  with  the  rosin  was  located  about  the  center  of  the  mercury 
bulb.  The  thermometer  with  tube  attached  was  immersed  in  cold 
water  in  a  400  Cc.  beaker  with  the  bottom  of  the  rosin  column  1  in. 
below  the  surface.  The  temperature  was  raised  about  30  per 
minute. 
In  the  cases  of  ]/\  in.  and  Y%  in.  columns,  it  will  be  noted  that  two 
temperatures  are  given.  The  lower  temperature  indicates  the  point 
at  which  the  rosin  is  soft  enough  for  the  water  to  enter  the  tube,  the 
other  being  the  point  at  which  the  water  breaks  through.  The  result 
is  of  course  merely  the  point  at  which  the  viscosity  is  so  reduced 
that  it  is  overcome  by  the  pressure  of  1  in.  of  water.  It  is  neces- 
sary that  the  heating  should  be  well  regulated.  If  heat  is  applied 
too  rapidly  it  will  naturally  result  in  a  higher  final  temperature  and 
a  wider  spread  between  the  two  points. 
The  capillary  tube  method  was  carried  out  as  follows :  Tubes 
about  1  Mm.  in  diameter  were  prepared  and  sealed  at  one  end. 
The  rosin  was  pulverized  between  two  pieces  of  paper.  About  2 
Cm.  of  the  tube  were  filled  with  the  powder,  and  it  was  attached  to 
the  thermometer  as  in  the  other  cases,  being  also  immersed  in  cold 
water  and  heated  as  before. 
A  reading  glass  was  used  to  observe  the  result  and  the  point  at 
which  the  particles  coalesced  - was  noted  as  the  melting  point.  It 
was  not  found  advisable  to  carry  the  heating  until  the  whole  of  the 
rosin  in  the  tube  became  clear  as  this  increased  the  range  of  personal 
error.  There  was  found  to  be  a  more  definite  indication  and  closer 
agreement  when  the  point  of  coalescence  was  noted. 
The  results  obtained  by  the  "  film "  method  are  for  practical 
purposes  the  same  as  those  obtained  by  the  "  capillary  "  method,  but 
the  tests  are  prepared  more  rapidly  and  with  much  less  trouble, 
especially  in  the  hands  of  unskilled  assistants.  The  end-point  is 
definitely  established  by  the  penetration  of  the  water. 
