MANUFACTURE,  IMPURITIES  AND  TESTS  OF  CHLOROFORM.  437 
specimen  that  is  used  should  be  subjected  to  the  scrutiny.  Some 
such  simple  tests  for  each  important  preparation  of  the  materia 
medica,  well  known  and  freely  applied  by  the  physician,  is  what 
is  now  most  needed  by  the  profession.  But  the  profession  should 
not  depend  upon  the  knowledge  and  research  of  the  chemical 
manufacturer  for  the  discovery  and  application  of  such  tests,  for 
very  obvious  reasons. 
When  equal  volumes  of  chloroform  and  pure  concentrated  sul- 
phuric acid  are  shaken  together,  and  then  allowed  to  separate, 
there  should  be  no  odor,  or  but  a  mere  faint  tinge  of  color  im- 
parted to  the  acid,  and  there  should  be  no  heat  developed  in  the 
mixture.  Any  chloroform  that  will  satisfy  these  simple  condi- 
tions, may  be  considered  pure,  and  may  be  used  with  confidence, 
while  all  that  will  not,  should  be  unequivocally  rejected.  In  the 
use  of  this  simple  and  easy  test,  the  indication  of  color  has  rela- 
tion to  the  deleterious  impurities,  and  that  of  temperature  to  the 
specific  gravity  or  dilution,  for  if  any  water  or  alcohol  be  present 
their  combination  with  the  acid  produces  rise  of  temperature. 
Chemically  pure  chloroform,  when  thus  shaken  with  the  acid, 
produces  no  sensible  effect  upon  either.  The  chloroform  of  the 
process  given,  causes  a  faint  tinge  of  color  in  the  acid  after  pro- 
longed and  vigorous  shaking,  and  produces  a  rise  of  temperature 
in  the  mixture  of  seven  or  eight  degrees,  not  perceptible  to  the 
hand.  The  amount  of  heat  developed  may  be  conveniently  noted 
by  observing  the  force  with  which  the  stopper  is  thrust  outward 
on  removing  it,  for  the  rarefaction  of  the  air  contained  with  the 
mixture  will  produce  a  pressure  upon  the  stopper  exactly  in  pro- 
portion as  it  is  warmed  by  the  mixture.  Differences  in  tempera- 
ture not  perceptible  to  the  hand,  may  be  detected  in  this  way  if 
the  necessary  precaution  is  observed  to  avoid  the  influence  of 
the  warmth  of  the  hand  in  shaking  the  bottle.  A  thermometer 
introduced  before  and  after  the  shaking  is,  however,  more  accu- 
rate and  reliable,  when  accuracy  is  necessary. 
This  is  by  no  means  the  only  qualitative  test  for  chloroform, 
but  as  it  is  the  most  simple  and  easy,  and  is  practically  reliable, 
it  is  useless  to  occupy  time  and  attention  with  others.  Few 
samples  of  chloroform  as  ordinarily  found  now,  will  meet  the 
requirements  of  this  test,  and  yet  the  preparation  is  generally 
much  better  than  it  was  four  or  five  years  ago. 
