OLEUM  ^THEREUM. 
59 
keeping,  any  decomposition  into  ultimate  elements,  or  any  substi- 
tions  occur,  with  the  exception  of  the  reproduction  of  the  small 
portion  of  sulphuric  acid,  and  the  well  known  effects  of  the  pres- 
ence of  this  acid  when  free  in  the  presence  of  loosely  combined 
hydrocarbons. 
The  practical  deductions  from  the  views  here  offered  are  that 
compound  spirit  of  ether  made  from  the  officinal  ethereal  oil  which 
may  have  undergone  this  separation  is  medicinally  nearly  equiva- 
lent to  that  made  from  the  freshly  prepared  oil,  the  small  pro- 
portion decomposed,  and  the  slight  acidity  of  such  preparation 
might  be  safely  disregarded  in  a  medicinal  point  of  view,  par- 
ticularly in  view  of  the  fact  that  the  well  made  compound  spirit 
of  ether  does  itself  become  slightly  acid  by  long  keeping,  especi- 
ally when  exposed  to  light  and  air.  It  is,  nevertheless,  much 
better  to  avoid  all  such  changes  whenever  it  is  possible  to  do  so  : 
and  this  introduces  the  second  question  of  the  inquiry  entrusted 
to  the  writer,  namely, 
"  Can  these  changes  be  retarded  ?" 
Upon  this  branch  of  the  subject  a  number  of  careful  experi- 
ments have  been  made,  with  results  so  definite  and  satisfactory, 
that  it  may  be  stated  that,  within  the  limits  of  the  ten  months 
allotted  to  the  preparation  of  this  report,  an  admixture  of  two 
parts  of  stronger  ether  with  one  part  of  ethereal  oil,  altogether 
prevents  the  separation  and  decomposition  of  the  oil,  although  it 
does  not  prevent  its  becoming  slightly  acid  to  litmus  paper.  The 
circumstance  that  the  action  upon  litmus  paper  is  slight  upon  first 
contact,  but  increases  rapidly  on  exposure  to  the  air,  renders  it 
probable  that  the  effect  is  due  to  the  formation  of  acetic  or  some 
other  organic  acid  from  the  alcohol  and  ethers  present,  as  in  the 
instance  of  sweet  spirit  of  nitre,  rather  than  to  a  decomposition 
of  the  heavy  oil  of  wine. 
Somewhere  near  the  above  designated  proportion  of  ether  is 
absolutely  necessary  to  effect  the  purpose  of  keeping  the  oil,  and 
it  does  not  matter  whether  this  proportion  be  diluted  with  alco- 
hol or  not,  since  alcohol  has  no  apparent  effect  either  to  hasten 
or  retard  the  separation  of  the  ethereal  oil.  For  instance,  it  was 
proved  by  experiment  that  no  less  than  four  parts  of  the  spirit 
of  ether  used  in  making  the  compound  spirit,  was  effective  in 
preserving  one  part  of  the  oil  from  the  changes,  and  the  steps  of 
