PRESERVATION  OF  MEDICINAL  PREPARATIONS.  555 
origanum,  marjoram,  fennel-seed,  Levant  worm-seed,  and  carda- 
mom, contain,  besides  acetic,  also  butyric  and  valerianic  acids, 
some  others  propionic  acid ;  rue-water  contains  the  aldehyd  of 
caprinic  acid,  and  valerian  water  valerianic  acid. 
To  obviate  the  rapid  decomposition  to  which  the  medicated 
waters  are  subject,  two  methods  have  been  proposed  :  1.  The 
vegetables  are  soaked  for  21  hours,  and  then  their  own  weight 
of  water  is  distilled  over,  which,  on  use,  is  to  be  sufficiently 
diluted :  2.  The  vegetables  are  merely  covered  with  water,  and 
macerated  for  a  day  ;  for  each  ounce  of  distilled  water,  which 
they  ought  to  yield  by  the  Pharmacopoeia,  5  grains  of  alcohol 
are  added,  and  by  distillation  so  many  scruples  are  obtained  as 
ounces  are  directed  by  the  Pharmacopoeia.  This  essence  keeps 
much  better  than  the  distilled  water,  and  any  medicated  water 
may  be  obtained  by  mixing  one  scruple  of  this  essecne  with  23 
scruples  of  water. 
Aqua  amygd.  amar.  and  aqua  laurocerasi  are  to  be  kept  in 
black  1  oz.  vials  sealed  with  wax ;  in  a  similar  manner  chlorine 
water  is  to  be  kept  in  black  1  oz.  glass  stopper  vials,  in  a  cool 
place  ;  it  will  retain  its  strength  for  years,  so  that  1  oz.  will 
entirely  peroxidize  16  grains  of  protosulphate  of  iron. 
4  Extracts. 
Nitrate  of  potassa,  chloride  of  potassium,  and  other  salts  are 
frequently  found  crystallized  in  old  aqueous  extracts,  which, 
with  the  constant  access  of  air,  are  gradually  more  or  less  con- 
verted into  apothegm  and  humus-like  products ;  the  decomposition 
may  be  partly  prevented  by  covering  their  surface  with  sugar  and 
adding  a  little  alcohol.  But  such  an  extract  may  be  compared  to 
a  rotten  apple,  the  brown  of  which  increases  in  size  by  concentric 
circles,  until  the  whole  of  it  has  been  converted  into  a  brown 
rotten  mass.  When  the  aqueous  extracts,  however,  immediately 
after  their  preparation,  are  filled  into  i,  1  or  2  oz.  wide-mouthed 
vials,  these  corked  and  treated  by  Appert's  method,  and  lastly 
sealed,  no  process  of  decomposition  will  ever  take  place.  This 
treatment  is  of  course  unnecessary  for  dry  aqueous  extracts. 
Hydro-alcoholic  extracts  generally  do  not  require  such  a 
treatment,  which  is  advisable  only  in  such  cases  where  they 
absorb  water  from  the  atmosphere,  like  extractum  belladonna, 
