NOTE  ON  MONOHYDRATED  SULPHURIC  ACID, 
175 
pliate  a  salt  resembling  the  compound  obtained  with  iodine  and 
sulphate  of  quinine.  It  is  made  by  dissolving  (at  30<^  C.)  10 
parts  of  the  sulphate  in  a  mixture  of  144  parts  of  acetic,  and  12 
parts  of  dilute  sulphuric  acid,  to  which  is  added  3  parts  of  iodine 
dissolved  in  115  parts  of  alcohol.  On  cooling,  plates  without 
definite  form  separate  from  the  solution. — Ohem.  News,  London, 
Jan,  ^th,  1861. 
NOTE  ON  MONOHYDRATED  SULPHURIC  ACID, 
By  Dr.  Lyon  Playfair. 
At  the  meeting  of  the  Royal  Society  of  Edinburgh,  on  the 
7th  instant.  Dr.  Playfair  drew  attention  to  the  researches  of 
Marignac  on  sulphuric  acid.  This  chemist  always  found  too 
much  water  in  monohydrated  sulphuric  acid,  and  fixed  its  speci- 
fic gravity,  as  Beneau  and  others  have  recently  done,  from  1-842 
to  1-845. 
It  is  well  known,  indeed,  that  this  hydrate  loses  anhydrous 
acid  when  distilled  or  boiled,  and  the  object  of  the  present 
communication  is  to  ascertain  the  exact  conditions  under  which 
this  loss  takes  place,  as  this  knowledge  is  of  importance  in  a 
practical  point  of  view. 
The  author  occasionally  found  on  distilling,  and  afterwards 
heating,  oil  of  vitriol,  that  acid  of  the  specific  gravity  of  1-848 
was  obtained,  but  at  other  times  the  specific  gravity  was  as  low 
as  1-842.  To  explain  this  difference,  the  following  experiments 
were  made : — 
1.  Sulphuric  acid,  having  a  specific  gravity  of  1-848,  and  a 
per  centage  of  anhydrids  of  81-62  by  the  alkalimeter,  was  put 
in  a  retort,  buried  in  hot  sand,  and  distilled.  The  distillate 
had  a  specific  gravity  of  1-840,  and  a  percentage  strength  of 
80-12.  It  had,  therefore,  lost  by  distillation  1^  per  cent,  of 
anhydrids. 
2.  The  weak  acid  got  by  the  last  experiment  was  heated  for 
half.an-hour  to  550*^  F.,  and,  after  cooling,  gave  an  acid  of 
1-84798  specific  gravity,  and  strength  of  81-615  anhydrids. 
3.  A  portion  of  this  acid  now  restored  to  its  full  strength  and 
specific  gravity,  was  violently  boiled  for  two  hours.    On  testing 
