252 
ON  SWEET  SPIRIT  OF  NITRE. 
Dublin,  8-7  ;  and  Edinburgh,  20  per  cent,  of  AeO-f  N03.  Dif- 
ference of  density,  which  would  make  a  slight  alteration,  has 
not  been  taken  into  account  here,  and  with  regard  to  these  cal- 
culations, there  can  be  no  doubt  as  to  the  Edinburgh  and  Dublin 
results.  The  London,  however,  have  gone  on  the  extravagant 
supposition  that  the  whole  N05  is  converted  into  N03,  and  united 
with  its  equivalent  of  AeO,  which  is  most  unquestionably  not  the 
case.  They  are  also  based  upon  the  supposition  that  the  alcohol 
in  the  London  product  is  of  sp.  gr.  -825.  The  impossibility  of 
finding  any  indisputable  data  rendered  these  necessary. 
Without  doubt  the  Edinburgh  process,  as  modified  by  the 
Dublin  College,  is  the  best.*  It  is  the  easiest,  the  safest  and 
most  productive ;  and  it  possesses  this  prime  qualification — its 
results  are  defined  and  definite.  There  is  no  dubiety  as  to  the 
quality  or  strength  of  the  product.  Its  composition  is  fixed,  and 
it  can  only  vary  by  internal  change  or  intentional  admixture. 
It  undergoes  both  of  these,  the  first  rendering  the  second  abso- 
lutely necessary.  The  sp.  eth.  nit.  of  the  Edinburgh  Pharma- 
copoeia changes  very  rapidly.  In  a  very  few  days  after  its 
preparation,  a  large  amount  of  free  acid  is  found  to  exist  in  it, 
which  goes  on  increasing ;  and  its  removal  must  be  accomplished 
before  the  sweet  nitre  can  be  dispensed,  unless  all  parties  are 
regardless  of  the  chemical  constitution  of  what  is  prescribed.  As 
an  instance,  let  us  suppose  a  very  common  case.  That  a  pre- 
scription contains  iodide  of  potassium  and  sweet  spirit  of  nitre. 
If  it  is  made  up  with  the  sweet  spirit  of  nitre,  almost  universally 
found  in  use ;  no  change,  or  a  very  small  one,  will  take  place 
upon  the  chemical  constitution  of  the  KI ;  but  if  made  up  with 
Sp.  Eth.  Nit.  of  the  Edinburgh  Pharmacopoeia,  which  has  been 
made  but  a  short  time — a  week  perhaps — then,  instead  of  KI 
and  a  colorless  fluid,  we  will  have  a  deep  brown  liquid,  containing 
KO-|-N05  and  free  iodine.  But  the  Edinburgh  preparation  is 
not  singular  in  undergoing  this  change.  It  takes  place  more  or 
less  in  every  sample  we  have  met  with,  and,  so  far  as  we  can 
*  The  N05  ordered  by  the  Edinburgh  Pharmacopoeia,  is  of  D.  1500,  which  is 
an  objection  of  more  force  than  at  first  sight  appears  ;  for  a  pure  acid  of  that  D. 
i9  scarcely  to  be  found  in  the  market.  Dr.  D.  Maclagen,  however,  has  shown, 
what  is  practically  valuable,  than  an  increased  quantity  of  a  weaker  acid  will 
answer  the  purpose  perfectly. 
