526 
ON  DILUTED  PHOSPHORIC  ACID. 
about  half  the  capacity,  invert  it  over  the  surface  of  the  liquid 
in  the  larger  dish,  and  apply  a  gentle  heat,  which  is  to  be  con- 
tinued until  the  complete  oxidation  of  the  phosphorus.  The  op- 
eration goes  on  slowly,  and  will  be  completed  at  the  expiration 
of  eight  hours,  attended  with  no  loss  of  phosphorus  and  with 
but  little  waste  of  nitric  acid,  as  will  be  seen  by  comparison  of 
the  quantity  used  with  the  quantity  of  acid  of  nearly  the  same 
strength  directed  by  the  London  College. 
When  the  phosphorus  has  entirely  disappeared,  the  small 
dish  should  be  removed,  and  the  heat  continued  until  no  trace 
of  nitric  acid  is  left.  The  product  now  weighs  about  11 J  ounces 
Troy,  measures  7  fluid  ounces,  and  requires  91  fluid  ounces  of 
distilled  water  to  reduce  it  to  the  London  standard,  sp.  gr.  1.064 
at  60°  Fahrenheit. 
Whether  diluted  phosphoric  acid,  prepared  as  above,  possesses 
any  advantage,  therapeutically,  over  a  boiled  solution  of  ordi- 
nary glacial  acid,  I  am  not  prepared  to  say  :  but  I  have  not 
succeeded  in  preparing  that  beautiful  crystalline  salt,  the  acid 
triphosphate  of  potassa,  with  the  latter  acid,  but  which  can  be 
prepared  with  great  facility  from  the  diluted  phosphoric  acid ; 
having  an  excess  of  acid  in  the  solution  when  set  aside  to  crys- 
tallize. 
The  expense  of  preparing  phosphoric  acid  by  the  process 
above  given,  may  easily  be  calculated  by  adding  to  the  cost  of 
the  given  quantities  of  phosphorus  and  nitric  acid,  the  value  of 
2J  pints  of  commercial  95  per  cent,  alcohol,  which  is  about  the 
quantity  consumed.  In  a  large  laboratory,  where  the  facilities 
for  the  application  of  heat  are  cheaper,  the  expense  of  prepar- 
ing the  acid  may  be  greatly  lessened.  The  proper  regulation 
of  the  heat  in  the  foregoing  process,  is  of  the  first  importance ; 
it  should  be  applied  gradually  until  the  yellow  fumes  caused  by 
the  nitric  oxide  coming  in  contact  with  the  atmosphere,  are  ob- 
served ;  it  should  remain  at  the  same  point  until  the  completion 
of  the  process  Journ.  and  Trans.  Maryland  Col.  Pharm.  Sep. 
1.  1858. 
