290     CHLOROFORM  AND  THE  TESTS  FOR  ITS  PURITY  IN  P.  B. 
attention  bestowed  upon  chloroform  has  been  given  to  its  an- 
aesthetic properties,  and  its  chemistry  has  been  very  nearly  set 
aside.  At  this  moment  it  has  different  names,  and  is  variously 
formulated ;  its  specific  gravity  is  given  by  some  as  1484,  and 
by  others  up  to  1-500;  the  changes  it  undergoes  by  what  we 
call  spontaneous  change,  and  by  reagents,  are  either  not  at  all 
or  ill-understood,  and  the  chemistry  of  its  production  from 
bleaching  powder  and  alcohol,  etc.,  is  yet  to  be  brought  out. 
We  need  not  wonder,  therefore,  that  its  characteristics  and  the 
tests  given  for  its  purity  should  be  found  somewhat  amiss.  The 
tests  given  in  the  British  Pharmacopoeia  are  four — 1st,  the  spe- 
cific gravity  1496 ;  2d,  "  not  colored  by  agitation  with  S  03  ;" 
3d,  it  leaves  after  evaporation  no  residue  and  no  unpleasant 
odor  ;  4th,  «  evolves  no  gas  when  potassium  is  dropped  into  it." 
It  is  to  the  last  of  these  that  your  attention  is  to  be  more  par- 
ticularly called,  but  a  few  words  upon  the  others  may  be  ad- 
vantageous. 
First,  then,  as  to  specific  gravity.  A  perfectly  pure  chloro- 
form will  give  a  gravity  of  1*500,  and  perhaps  a  very  little 
above  that;  but  for  a  commercial  article,  well  and  carefully 
manufactured,  1496  is  a  perfectly  fair  standard.  As  it  is  sent 
out  by  manufacturers  at  present,  we  believe  you  will  always  find 
it  to  be  from  1498  to  1*500.  Certainly  anything  below  1496 
ought  to  be  held  wrong.  Here  the  editors  of  the  "  British 
Pharmacopoeia"  proceed  upon  a  sound  principle;  eschewing 
that  myth,  "  absolute  chemical  purity,"  they  allow  a  fair  margin, 
and  no  more;  but,  as  we  shall  see,  it  should  have  been  allowed 
all  through. 
The  second  test,  "  not  colored  by  agitation  with  S  03,"  is  un- 
fortunately worded.  An  impure  chloroform  agitated  with  S  03 
colors,  and  that  deeply,  the  S  03,  while  the  chloroform  itself  is 
left  colorless,  or  all  but  colorless.  It  may  be  almost  certainly 
held  that  what  is  meant  is,  that  when  agitated  with  S  03,  it  gives 
no  color  to  the  S  03.  "  Colorless,"  however,  must  be  taken  cum 
grano  salis.  A  well-prepared  chloroform  will  stand  the  test  pro- 
vided the  search  for  color  be  made  by  transmitted  light  ;  but 
scarce  any  can  be  found  which  will  not  show  a  very  faint  tint 
in  the  S  03,  if  a  piece  of  white  paper  be  put  behind  the  tube. 
Moreover,  the  test  requires  precaution  in  its  use.    A  somewhat 
