52  CONTAMI57ATION  OF  HYDROCHLORIC  WITH  SULPHURIC  ACID. 
therefore,  found  in  the  farthest  and  coolest  receivers,  and  escape 
detection  by  the  chloride  of  calcium  test.  The  hydrochloric  acid, 
which  when  freshly  made  contains  these  lower  oxides  of  sulphur, 
hut  no  sulphuric  acid,  will,  however,  on  keeping,  soon  begin  to 
show  sulphuric  acid,  and  finally  will  contain  this  acid  alone,  all 
the  lower  oxides  being  progressively  and  spontaneously  converted 
into  the  higher  one. 
When  hydrogen  is  liberated  in  a  nascent  state  in  the  presence 
of  these  lower  oxides  of  sulphur,  they  are  all  reduced  and  con- 
verted into  sulphuretted  hydrogen,  sulphur  and  water,  leaving 
the  solution  comparatively  free  from  sulphur  compounds.  Thus 
it  happens  that  when  freshly  made  hydrochloric  acid,  free  from 
sulphuric  acid,  but  containing  the  lower  oxides,  is  used  for 
making  the  chlorides  of  iron  or  zinc,  the  resulting  chlorides  will 
be  free,  or  comparatively  so,  from  sulphuric  acid  and  sulphates, 
while  a  portion  of  the  same  acid,  if  kept  long,  will  contain  sul- 
phuric acid  and  be  comparatively  free  from  the  lower  oxides  of 
sulphur.  Hence  the  escape  of  sulphuretted  hydrogen  during 
the  reaction  with  these  metals  is  an  easy  practical  test  for  the 
lower  oxides,  but  not  for  the  higher. 
This  best  grade  of  hydrochloric  acid  is  often  not  accessible  to 
the  writer,  unless  he  waits  for  it  to  be  made,  and  then  it  is  re- 
ceived quite  fresh  and  new,  and  is  at  once  used  for  making  the 
chlorides  of  iron  and  zinc.  It  then  gives  olF  sulphuretted  hydro- 
gen so  copiously  that  it  is  necessary  to  make  the  solution  out  of 
doors,  and  yields  chlorides  which  are  practically,  though  not  ab- 
solutely, free  from  sulphates.  Portions  of  the  same  lot  of 
hydrochloric  acid  stored,  and  used  subsequently,  have  been 
found  to  contain  largely  of  sulphuric  acid  and  nothing  else. 
Hence  the  conclusion  that  nascent  hydrogen  decomposed  sul- 
phuric acid  in  this  reaction  and  thus  yielded  the  floating  sulphur, 
and  the  escaping  sulphuretted  hydrogen  was  accepted  on  very 
insufficient  grounds  and  erroneously  put  forth. 
All  of  which  is  respectfally  submittedr-  in  answer  to  Query 
No.  31. 
Brooklyn^  August  14if7i,  1868. 
— Proc.  Amer,  Pharm,  Assoc. ^  1868. 
