CONTAMINATION  OF  HYDKOCHLORIC  WITH  SULPHURIC  ACID.  51 
is  no  evidence  whatever  of  the  presence  of  sulphuric  acid,  and 
therefore  that  the  statement  of  the  writer  was  entirely  erroneous, 
and  Mr.  Maisch  was  quite  right  upon  the  point  of  accurate 
knowledge  which  he  raised. 
It  became  then  a  matter  of  interest  to  the  writer  to  ascertain 
how  the  error  had  occurred.  This  was  satisfactorily  determined, 
and  may  interest  the  Association  as  a  part  of  the  history  of  the 
hydrochloric  acid  of  commerce. 
This  acid  is  often,  if  not  generally,  made  by  the  best  makers 
by  decomposing  common  salt  in  iron  retorts  by  means  of  sul- 
phuric acid  and  heat.  The  gaseous  products  and  vapors  from 
the  decomposition  are  conducted  into  a  series  of  three  or  four 
receivers  or  Wolf's  bottles  containing  water  for  the  absorption  of 
the  hydrochloric  acid  gas.  But  the  entering  tubes  of  these 
receivers  do  not  dip  into  the  water  as  in  the  ordinary  Wolf's 
arrangement,  and  the  absorption  of  the  gas  is  therefore  slow  and 
passive,  only  facilitated  occasionally  by  stirring.  From  the  last 
receiver  an  ascending  series  of  four  or  more  shallow  glass  vessels 
lying  upon  an  inclined  plane,  and  discharging  by  gravitation  one 
into  the  other,  and  the  lowest  one  into  the  last  receiver,  are  so 
placed  as  to  receive  at  the  highest  end  supplies  of  fresh  water 
from  time  to  time.  This  water,  flowing  downward,  meets  the 
current  of  yet  unabsorbed  gas  from  the  last  receiver,  and  absorbs 
it  all  in  its  progress  into  the  last  receiver,  which  finally  contains 
the  best  hydrochloric  acid  of  the  process,  and  of  the  common 
market.  This,  when  put  up  for  the  market,  often  shows  little  or 
no  sulphuric  acid  by  the  manufacturer's  test,  which  is  solution 
of  chloride  of  calcium.  The  reaction  which  occurs  in  the  cast- 
iron  retort  from  impure  materials,  and  at  a  high  temperature  at 
the  close,  gives  various  gaseous  products,  among  which  the  most 
common  and  most  copious  are  the  lower  oxides  of  sulphur.  It 
has  generally  been  supposed  with  reason  that  small  quantities  of 
sulphuric  acid  also  distil  over,  and  that  thus  the  hydrochloric 
acid  becomes  contaminated  with  sulphuric  acid.  This  is  doubt- 
less always  true  with  regard  to  the  contents  of  the  first  receiver, 
but  is  practically  impossible  to  any  after  the  second  I  Not  so 
with  regard  to  the  lower  oxides  of  sulphur,  however,  some  of 
which  are  gaseous  and  all  far  less  easily  condensed.    These  are, 
