SULPHUROUS  ACID. 
243 
solution  of  iodine  of  the  strength  indicated  by  the  Pharmacopoeia, 
jQ  of  an  atom  (12*7  grains)  in  1000  grain-measures  (the  ac- 
curacy of  the  iodine  solution  being  coni&rmed  by  the  volumetric 
solution  of  hyposulphite  of  soda),  gave  results  which,  combined 
with  the  various  specific  gravities  of  the  solutions  described, 
could  only  point  to  one  conclusion,  viz.,  that  the  Pharmacopoeia 
solution  did  not  coincide  in  its  described  spec.  grav.  as  compared 
with  its  percentage  of  acid  ;  for  a  solution  of  1*040  indicated  but 
7*8  per  cent,  of  real  acid,  instead  of  9*2  per  cent.,  or  in  other 
words,  if  the  spec.  grav.  was  correct,  the  strength  was  an  error, 
or  viee  versd. 
The  Brit.  Pharm.  1864  directed  an  acid  of  1.040  spec,  grav., 
but  only  indicated  the  numbers  of  measures  of  iodine  solution  re- 
quired for  its  saturation  as  equivalent  to  8'3  per  cent. 
This,  therefore,  is  an  approximation  to  the  result  I  have  ob- 
tained. 
In  an  excellent  review  of  the  officinal  acids  by  Mr.  C.  H. 
Wood,  article  "  Sulphurous  Acid,"*  it  is  said,  "  This  acid  is  of 
the  same  strength,  and  is  prepared  in  the  same  manner  as 
before." 
It  is  certainly  of  the  same  specific  gravity,  viz.,  1*040,  but  I 
find  by  calculation  that  88  measures  of  iodine  solution  less  in 
1*000  measures  are  indicated  than  by  the  B.  P.  1867,  an  equiva- 
lent of  nearly  1  per  cent,  real  acid.  The  two  solutions  of  the 
two  pharmacopseias,  although  of  the  same  specific  gravity,  can- 
not, then,  be  of  the  same  strength. 
The  manufacture  of  the  acid  on  the  large  scale,  up  to  even 
the  highest  point  to  which  I  have  arrived,  is  next  to  impossible. 
I  will  quote  the  remarks  of  a  chemist,  in  a  letter  upon  this  sub- 
ject to  me,  who  is  in  the  habit  of  making  tons  yearly.    He  says, 
I  obtain  a  solution  of  1  030  easily  (comparatively) ;  and  in  cold 
weather  and  a  slow  current  of  gas,  ordinarily  I  get  acid  from 
1*025-30." 
Through  the  kindness  of  Messrs.  May  and  Baker,  Battersea 
I  have  been  favored  by  their  chemist,  Mr.  Tyrer,  with  the  re- 
sult of  two  experiments  made  on  a  very  large  scale,  and  under 
the  most  favorable  circumstances. 
*  Pharm.  Journ.  Yq].  IX,  page  64. 
