362  Spirit  of  Nitrous  Ether.  { Xm)XrJ%rm' 
having  the  sp.  gr.  0*822  ;  of  the  first  "  experimental "  distillation, 
0*8225;  of  the  second  u  experimental "  distillation,  0*825.  With 
these  results  before  me,  I  naturally  began  to  inquire  into  the  correct- 
ness of  the  pharmacopoeial  statement,  when  it  soon  became  evident 
that,  unless  great  condensation  occurs  by  the  solution  of  nitrous  ether 
in  stronger  alcohol,  the  statement  of  the  U.  S.  P.  must  be  based  on 
error. 
The  "  Pharmacopoeia,"  after  giving  the  specific  gravity  of  the  spirit, 
states  that  it  "  contains  5  per  cent,  of  its  peculiar  ether."  Without 
pausing  to  consider  whether  this  statement  is  correct  or  incorrect,  and 
assuming  it  to  be  true  for  pure  ether,  the  question  arises,  whether  the 
percentage  given  is  meant  to  be  percentage  by  weight  or  percentage  by 
volume.  Neither  the  "  United  States  Dispensatory  "( 13th  ed.)  nor 
u  Parrish's  Pharmacy"  (4th  ed.)  throw  any  light  on  this  point.  The 
"  British  Pharmacopoeia,"  however,  states  of  its  own  preparation:  u  If 
it  is  agitated  with  twice  its  volume  of  saturated  solution  of  chloride  of 
calcium,  in  a  closed  tube,  2  per  cent,  of  its  original  volume  will  separate 
in  the  form  of  nitrous  ether,  and  rise  to  the  surface  of  the  mixture."  It 
does  not  say  that  the  preparation  should  contain  10  per  cent,  of  nitrous 
ether;  but  one  of  the  editors  of  "  Pareira's  Materia  Medica"  (abridged 
ed.,  1872),  probably  Prof.  Redwood,  commenting  on  the  process,  says: 
tc  The  separation  of  2  per  cent,  of  nitrous  ether  indicates  the  presence 
of  about  10  per  cent,  of  nitrous  ether,  8  per  cent,  remaining  dissolved 
in  the  mixture."  It  is,  therefore,  safe  to  assume  that  the  U.  S.  P. 
intends  to  indicate  volume  and  not  weight  per  cent.1 
If,  then,  spirit  of  nitrous  ether  is  composed  of  5  per  cent.,  by  vol- 
ume, of  absolute  nitrous  ether,  sp.  gr.  0*94.7,  and  95  per  cent.,  by 
volume,  of  stronger  alcohol,  sp.  gr.  0*817,  what  should  be  its  sp.  gr., 
if  no  condensation  occurs  ? 
5  volumes  of  nitrous  ether,  sp.  gr.  o  947,  weigh  4735  parts, 
95  volumes  of  stronger  alcohol,  sp.  gr.  0-817,  weigh       77*615  parts, 
100  volumes  of  spirit  of  nitrous  ether  weigh  82  350  parts, 
indicating  a  specific  gravity  of  0*8235,  which,  while  totally  at  variance 
with  the  "  Pharmacopoeia,"  corresponds  very  nearly  to  the  specific 
gravities  obtained  by  me. 
1  Since  writing  the  above  I  have  had  opportunity  to  consult  the  latest  (14th) 
edition  of  the  "United  States  Dispensatory,"  in  which  (page  1445)  I  find  the 
following  statement:  "The  sweet  spirit  of  nitre  obtained  by  the  old  formula  was 
estimated  to  contain  4  per  cent,  in  'volume  of  nitrous  ether. 
