466        Preparation  of  Diluted  Pliosphoric  Acid,  {^''o^t^'JwrL'^' 
As  far  as  the  apparatus  is  concerned,  it  will  readily  be  seen  that 
the  latter  process  is  much  more  simple  ;  the  danger  of  explosion  and 
fracture  is  almost  impossible ;  most  of  the  nitric  acid  is  condensed, 
and  trickles  down  the  funnel  into  the  capsule,  while  the  manipula- 
tion is  easier,  and  the  operation  can  be  carried  to  completion  in  the 
vessel  in  which  it  was  commenced. 
In  both  processes,  however,  the  nitric  acid  is  used  in  a  very  dilute  form. 
According  to  the  experience  of  the  writer  this  occasions  a  waste  of 
time  and  is  attended  with  no  advantage.  The  action  of  the  dilute 
acid  on  the  phosphorus  is  very  feeble,  and,  in  operating  on  larger 
quantities — say  ten  pounds  of  phosphorus — eight  or  ten  days  are  re- 
quired for  the  solution.  The  acid  need  not  be  weaker  than  that  of 
sp.  gr.  1-24.  At  this  strength  there  is  no  danger  of  explosion,  or  a 
too  rapid  action.  After  many  and  cautious  trials  I  have  now  no  hesi- 
tation in  operating  on  the  above-named  quantity  of  phosphorus,  with 
a  carboy  of  acid  of  the  strength  named,  and  by  so  doing  the  solution 
may  be  effected  in  from  fifteen  to  twenty  hours.  Nothing  at  all  ap- 
proaching to  an  explosion  has  ever  occurred,  but  the  precaution  is 
always  taken  to  have  a  quantity  of  distilled  water  near  at  hand,  so 
that  it  can  be  at  once  added  if,  by  the  concentration  of  the  acid,  the 
action  becomes  at  all  violent. 
In  driving  off  the  excess  of  nitric  acid,  after  the  phosphorus  has 
been  dissolved,  a  considerable  degree  of  heat  will  be  required,  and  the 
greatest  care  should  be  taken  that  the  acid  has  become  quite  cool,  be- 
fore adding  the  water  for  dilution.  If  this  is  neglected,  and  the 
water  is  added  to  the  hot  acid,  an  explosion  is  inevitable,  owing  to 
the  rapid  change  of  the  water  into  .the  gaseous  form.  Indeed,  it  would 
be  much  less  dangerous  to  pour  water  into  a  ladleful  of  melted  lead. 
For  this,  as  well  as  all  other  operations  in  which  solutions  of  acid 
or  alkali  are  employed,  the  use  of  enamelled  iron  vessels  must  be 
avoided  ;  nothing  but  porcelain,  or  at  least  wedgewood,  should  be  used. 
In  this  connection  the  writer  would  protest  against  the  use  of  enam- 
elled vessels  for  any  of  the  purposes  of  pharmacy  in  which  an  acid, 
or  alkali  proof  material  is  required.  I  have  never  yet  met  with  a 
vessel  of  this  kind  that  was  at  all  reliable,  being  either  of  a  material 
readily  acted  on,  or  pierced  with  minute  holes,  exposing  the  under- 
lying iron  and,  consequently,  contaminating  everything  with  that 
metal. — Canadian  Pharm.  Journ.^  August,  1871. 
