242 
SULPHUROUS  ACID. 
in  many  laboratories  it  is  merely  a  by-product, — but  rather  from 
some  practical  difficulties  in  making  such  a  strong  solution  on 
the  large  scale. 
The  following  experiments  were  made  with  a  view  to  deter- 
mine the  strength  of  the  acid  that  could  be  obtained  by  the 
officinal  process,  and  to  ascertain  the  circumstances  most  favor- 
able to  its  production  : — 
1.  Oil  of  vitriol  was  reduced  in  a  flask  by  charcoal,  the  re- 
sulting gas  after  passing  through  the  wash-bottle  was  allowed 
to  slowly  bubble  through  the  water  intended  for  its  solution, 
this  being  kept  at  the  temperature  of  the  laboratory  (65°  to  70° 
F.) ;  after  eight  hours  nearly  2  per  cent  was  found  to  have  been 
dissolved,  the  solution  having  a  spec.  grav.  of  1-009  at  60°  F. 
2.  The  current  of  gas  produced,  as  in  previous  experiment, 
allowed  to  pass  slowly  through  water  for  36  hours.  Solution 
nearly  6  per  cent.,  spec.  grav.  1*030. 
3.  Gas  passed  through  water  slowly  under  a  pressure  of  one 
lb.  (2  inches  mercury)  for  8  hours  under  same  conditions  as 
before.    Solution  5  per  cent.,  spec.  grav.  1*028. 
4.  Solution  made  under  2  lbs.  pressure  (4  inches  mercury)  for 
8  hours,  indicated  5J  per  cent.  Spec.  grav.  1*030.  (This  clear 
ly  show^ed  the  advantage  of  using  pressure,  the  solution  of  the 
gas  being  more  readily  affected. 
5.  Iced  water  was  then  kept  around  the  receiver  ;  the  gas  was 
slowly  passed  through  for  16  hours,  resulting  in  a  solution  of 
nearly  9  per  cent.,  and  1*045  spec.  grav. 
6.  Increased  pressure  repeatedly  tried,  the  result  being  in- 
variably the  fracture  of  the  generator. 
Not  having  other  available  apparatus  at  hand,  and  as  I  had 
obtained  much  beyond  the  spec.  grav.  of  the  Pharmacopoeia  so- 
lution, and  had  almost  approached  its  strength, — from  want  of 
leisure  I  did  not  continue  my  research. 
The  various  solutions  carefully  examined*  with  a  volumetric 
*  In  weighing  the  acid  for  examination,  I  always  counterpoised  in  the 
beaker  in  which  the  acid  was  to  be  weighed  about  one  ounce  of  cold 
water,  as  I  found  this  prevented  the  loss  of  gas  of  the  strong  solution 
which  invariably  resulted  if  weighed  alone,  the  acid  being  taken  out  with 
a  pipette,  the  analysis  of  each  specimen  was  thus  eflPected  rapidly — cer- 
tainly in  three  or  four  minutes. 
