24  Vesicating  Principle  of  Croton  Oil        { Am  jj™1"-^ arm- 
In  another  paper  I  have  given  the  results  of  my  work,  so  far,  on 
this  purgative  oil.  Tn  this  paper  I  show,  in  the  first  place,  more 
exactly  what  the  conditions  are  which  affect  the  solubility  of  croton  oil 
in  alcohol,  maintaining  and  extending  my  previous  conclusions.  In 
the  next  place,  I  proceed  to  determine  whether  the  oil  soluble  in  alcohol 
is  itself  the  vesicating  principle,  or  what  part  of  it  has  that  power. 
The  Solubility  of  Croton  Oil  in  Alcohol. — When  alcohol  (sp.  gr.  '794 
to  *800)  is  mixed  in  equal  volumes  with  English  pressed  croton  oil, 
perfect  solution  takes  place,  the  mixture  being  permanent  at  all  ordinary 
temperatures,  and  this  is  equally  true  when  any  less  quantity  of  alcohol 
is  used.  When,  however,  the  proportion  of  alcohol  to  croton  oil  becomes 
as  seven  volumes  to  six,  or  any  larger  proportion  of  alcohol,  then  a 
part  of  the  croton  oil  separates.  This  part  varies  in  quantity,  in  the 
case  of  different  samples  of  oil,  in  accordance  with  the  conditions  noted 
in  my  former  paper.  It  is  an  interesting  fact  that  that  portion  of  the 
croton  oil  which  separates  when  the  alcohol  is  in  excess  is  afterwards 
insoluble  in  any  proportion  of  alcohol.  But  that  portion  of  the  oil 
dissolved  by  alcohol  is,  when  separated,  soluble  in  all  proportions. 
In  the  discussion  following  my  former  paper,  Professor  Redwood 
remarked  on  an  apparent  discrepancy  between  my  results  on  this  point 
and  some  experiments  made  by  himself  some  years  previously. 
In  the  experiments  reported  by  Professor  Redwood,  croton  oil  and 
alcohol  were  used  in  equal  volumes  only  and  found  perfectly  miscible. 
This  result,  so  far  as  it  goes,  agrees  exactly  with  my  own,  and  no  doubt 
if  Professor  Redwood  had  employed  other  proportions  than  those  given 
his  results  would  also  have  coincided  with  mine.  The  usual  statements 
regarding  the  solubility  of  croton  oil  in  alcohol  as  found  in  many  text- 
books, and  incidentally  revived  by  Mr.  A.  H.  Allen  in  his  recent  paper 
on  "The  Chemistry  and  Examination  of  Fixed  Oils"1  are  shown  by 
my  experiments  to  be  inaccurate. 
Search  for  the  Vesicating  Principle. — Some  of  the  characters  of  the 
alcohol-soluble  croton  oil,  which  has  been  shown  to  contain  the  vesi- 
cating principle  I  have  described  in  the  previous  paper,  to  which 
reference  has  already  been  made.  The  more  important  of  these  char- 
acters, together  with  others  since  observed,  are  as  follows : — At  60°F. 
this  oil  is  of  a  brown  color,  and  holds  in  suspension  a  number  of  acicu- 
lar  crystals  soluble  on  warming.  It  has  a  strong  characteristic  smell 
of  croton  oil,  a  persistent  burning  taste,  and  readily  produces  pustules 
1  "Jour.  Soc.  Cheni.  Ind.,"  February  28,  1883. 
