244 
SULPHUROUS  ACID. 
A  charge  of  200  lbs.  charcoal  and  140  lbs.  oil  of  vitriol  was 
placed  in  a  still  of  120  gallons'  capacity ;  the  gas  washed  and 
passed  through  a  series  of  Woulfe's  bottles,  the  exit  pipe  from 
the  last  bottle  being  weighted  at  6  lbs.  pressure.  In  temperate 
weather  by  this  method  an  acid  from  1*033  to  1*035  con  be  pro- 
duced, and  by  passing  through  a  second  charge  of  gas  from  a 
fresh  supply  of  oil  of  vitrol,  a  solution  of  l-036_to  1*038  can  be 
produced, — but  this  only  on  cold  nights  and  working  very  slow- 
ly ;  if  the  gas  is  passed  rapidly,  more  is  lost  than  gained. 
The  second  experiment  was  but  a  modification  of  this,  sub- 
stituting at  the  last  of  the  Woulfe's  bottles  a  pressure  produced 
by  a  column  of  water  of  12  feet  (6  lbs.  pressure),  with  plugs 
inserted  at  3  feet  intervals,  so  that  by  withdrawing  them  the 
pressure  could  be  regulated.  This  means  of  producing  pressure 
was  adopted  in  preference  to  the  valve,  which  invariably  cor- 
roded, as  it  gave  a  ready  means  of  allowing  the  carbonic  acid 
and  carbonic  oxide  to  escape.  The  result,  however,  was  an 
acid  of  only  1.038  specific  gravity,  as  in  previous  experiment. 
To  work  regularly  at  this  amount  of  pressure  would  be  anything 
but  desirable. 
The  U.  S.  Pharm.  orders  a  solution  of  1*035  specific  gravity 
no  strength  is  however  named,  neither  is  a  process  given  for  its 
estimation  ;  it  does,  however,  direct  the  solution  to  be  put  into 
half-pint  bottles,  well  stoppered,  and  kept  in  a  cool  place.  In  the 
1837  edition  of  the  French  Codex,  a  solution  of  thirty-seven 
volumes  is  directed,  the  specific  gravity  described  as  1*053. 
The  gas,  however,  is  made  by  the  reduction  of  oil  of  vitriol 
with  mercury,  which  gives  a  product  nearly  pure.  This  is 
almost  identical  with  my  result,  taking  into  consideration  the 
quantity  of  carbonic  acid  necessarily  dissolved  with  the  sulphur- 
ous acid  under  pressure. 
It  cannot  for  one  moment  be  doubted  that  a  solution  of  much 
greater  strength  than  any  here  indicated  could,  in  the  experi- 
menting room,  under  certain  circumstances,  be  made  without 
great  difficulty  (using  copper  and  sulphuric  acid  to  obtain  the 
sulphurous  acid) ;  for  we  have  the  unquestionable  authority  of 
Bunsen  upon  the  subject,  who  is  thus  cited  by  Miller,  in  his 
'Elements  of  Chemistry Water  will  absorb  at  32°  F.,  68*8 
volumes  ;  at  59°,  43*5  volumes ;  and  at  75°,  32  volumes." 
