448 
NOTE  ON  DISTILLED  SULPHURIC  ACID. 
oil  of  vitriol,  but  distilled  sulphuric  acid,  and  this  is  described 
as  monohydrated  sulphuric  acid  (HC^SOj ),  the  specific  gravity 
of  which  is  represented  as  1*846. 
Having  had  occasion  in  my  lectures  on  the  British  Pharma- 
copoeia to  remark,  with  reference  to  sulphuric  acid,  that  in  the 
processes  and  descriptions  given  in  that  work  there  are  some 
inconsistencies  and  errors,  I  have  been  called  to  account  for 
making  such  a  statement  on  what  has  been  assumed  to  be  in- 
sufficient grounds. 
The  subject  is  one  on  which  I  had  worked  a  good  deal  some 
years  ago,  and  my  remarks  were  partly  founded  on  results  then 
obtained,  and  partly  on  the  published  investigations  of  others. 
I  have  since  repeated  some  of  the  experiments  to  which  I  re- 
ferred, and  wish  on  one  or  two  points  to  lay  the  results  before 
the  meeting. 
Forty-eight  fluid-ounces  of  commercial  oil  of  vitriol,  of  sp. 
gr.  1843,  were  put  into  a  small  platinum  still  with  one  ounce 
of  sulphate  of  ammonia,  and  the  mixture  submitted  to  frac- 
tional distillation.  The  first  distillate,  consisting  of  seven  fluid 
ounces,  was  rejected.  The  three  subsequent  distilates,  consist- 
ing of  three  fluid  ounces,  five  and  a  half  fluid  ounces,  and  six 
and  a  half  fluid  ounces,  had  all  very  nearly  the  same  specific 
gravity,  ranging  from  1841*3  to  1841*5.  The  next  distillate, 
consisting  of  seven  and  a  half  fluid  ounces,  had  a  sp.  gr.  1842*3, 
and  the  next,  consisting  of  six  fluid  ounces,  had  a  sp.  gr.  1842*5. 
I  observed  that  all  these  products  had  a  slight  smell  of  sul- 
phurous acid,  the  production  of  which  I  could  only  account  for 
by  assuming  that  a  portion  of  the  sulphuric  acid  was  decom- 
posed in  contact  with  the  heated  platinum  vessel  at  the  temper- 
ature required  for  the  distillation.  I  ascribed  to  this  decompo- 
sition the  low  specific  gravity  of  the  product  as  compared  with 
what  is  indicated  in  the  Pharmacopoeia,  and  I  therefore  relin- 
quished the  further  use  of  the  platinum  still. 
Another  operation  was  performed  in  a  glass  retort,  as  des- 
cribed in  the  Pharmacopoeia.  The  specific  gravity  of  the  oil 
of  vitriol  operated  upon  in  this  case  was  1844,  this  being  the 
densest  commercial  oil  of  vitriol  I  was  able  to  get.    The  pro- 
