436   MANUFACTURE,  IMPURITIES  AND  TESTS  OF  CHLOROFORM. 
of  some  acids  are  controlled  by  combination.  Thus,  if  the 
balance  of  affinities  is  disturbed  in  the  direction  of  decomposition, 
the  disturbing  forces  being  equally  efficient  for  recomposition 
when  material  is  present  in  the  proper  condition — alcohol,  the 
original  matrix  being  present,  the  chain  is  again  closed  and 
complete. 
With  regard  to  the  effect  of  sulphuric  acid,  it  is  true  that  the 
best  manufacturers  in  Edinburgh,  where  perhaps  chloroform  is 
best  made  and  most  used,  do  purify  their  product  with  the  acid, 
but  then  they  distil  it  from  the  acid  after  having  combined  the 
latter  with  baryta.  Thus  after  the  acid  has  performed  its  office 
of  destroying  all  the  impurities,  it  is,  in  effect,  prevented  from 
carrying  off  with  it  the  last  portions  of  alcohol  and  water,  by 
having  presented  to  it  a  substance  for  which  it  has  a  superior 
affinity,  and  for  which  it  abandons  the  alcohol  and  water,  and 
these  latter  are  again  seized  by  and  carried  over  with  the  chloro- 
form. This  process  of  purification  has  been  long  used,  and  is 
probably  unobjectional  in  effect.  It  is,  however,  not  better  than 
that  above  given,  while  it  is  far  more  troublesome  and  expensive. 
The  risk  of  decomposition  from  too  high  density  is,  however, 
one  of  the  very  least  that  commercial  chloroform  has  to  en- 
counter, for  where  one  specimen  is  found  to  be  above  1.49, 
hundreds  are  found  below  it.  Indeed,  it  is  very  rare  to  meet 
with  a  specimen  whose  density  is  above  1.49,  the  greater  number 
by  far  being  about  1.46  to  1.48.  Low  specific  gravity  alone, 
however,  does  not  render  the  preparation  noxious  or  bad,  as  is 
shown  by  the  common  use  of  a  tincture  of  chloroform.  Yet, 
when  of  a  low  specific  gravity,  it  is  almost  invaribly  bad,  from 
the  simple  fact  that  the  manufacturer  in  leaving  it  thus,  must 
leave  other  impurities  in  it  which  would  have  been  in  great 
measure  removed  by  the  washings  required  to  free  it  from  alcohol. 
In  short,  the  bad  effects  which  are  attributed  to  chloroform, 
and  which  have  brought  upon  this  anaesthetic  a  large  share  of 
the  distrust  in  which  it  is  held,  are,  in. the  opinion  of  the  writer, 
due  to  the  presence  in  it  of  foreign  deleterious  compounds,  which 
are  the  result  of  faulty  preparation  and  bad  materials. 
Fortunately  these  deleterious  compounds  may  be  easily  de- 
tected, and  by  very  simple  means  within  the  reach  and  practice 
of  every  one  who  can  have  occasion  to  use  chloroform  ;  and  every 
