350 
HINTS  TO  DISPENSERS. 
avoid  using  a  mortar  as  much  as  possible,  thereby  preventing 
unnecessary  trouble  and  straining,  as  liquids  very  rarely  come 
out  of  a  mortar  in  the  same  condition  as  they  entered  it.  Many 
of  the  soluble  salts,  such  as  bicarbonate  of  potash,  bicarbonate  of 
soda,  Rochelle  salts,  etc.  (if  of  the  best  make)  are  perfectly  and 
readily  soluble  in  ordinary  aqueous  vehicles,  yet  how  common 
the  practice  of  rubbing  them  down  in  mortars,  thereby  running 
the  risk  of  contaminating  them,  besides  losing  time.  The  heavy 
carbonate  of  magnesia  and  trisnitrate  of  bismuth  may  also,  as  a 
rule,  be  slipped  into  the  bottle,  without  the  necessity  of  dirtying 
a  mortar.  All  soluble  scaly  preparations  dissolve  more  readily 
in  the  bottle  than  by  rubbing  in  a  mortar.  On  the  other  hand, 
there  are  many  cases  in  which  the  use  of  the  mortar  is  absolutely 
necessary  to  the  production  of  an  elegant  mixture  ;  as  when 
bulky  powders  are  prescribed,  which  must  be  gradually  rubbed 
up  with  the  liquid ;  also  when  considerable  effervescence  takes 
place  in  mixing ;  when  hot  water  is  required  for  solution ;  when 
crystals  are  to  be  broken  down  and  dissolved,  or  rubbed  up  when 
insoluble.  When  extracts  are  ordered  in  mixtures,  the  readiest 
means  of  dissolving  them  is  by  working  them  into  a  smooth 
liquid  paste  on  a  slab  with  a  palette  knife,  and  then  scraping  off 
into  a  measure  containing  more  of  the  vehicle,  and  gently  mix- 
ing with  the  knife.  Oil  of  almonds  and  olive  oil,  when  ordered 
with  liquor  potassae,  form  a  very  nice  emulsion,  by  diluting  the 
alkali  freely,  and  shaking  the  two  together.  When  compound- 
ing a  mixture  containing  ingredients  which  act  chemically  upon 
esach  other,  it  is  advisable  to  keep  them  as  far  apart,  and  as  much 
diluted,  as  possible.  Chloroform,  creasote,  and  essential  oils, 
should,  if  any  tinctures  are  present,  be  dissolved  in  them  prior 
to  being  added  to  the  mixture.  In  rubbing  oil  of  cubebs  or 
other  essential  oils  in  large  quantities  with  mucilage,  great  care 
is  necessary  to  avoid  an  insoluble  compound  forming :  this  may 
be  prevented  by  judicious  diluting  during  the  process.  Gallic 
acid  should  be  dissolved  in  hot  water,  as  also  should  quinine,  if 
there  be  no  other  solvent  present ;  but  care  must  be  taken  to 
ascertain  that  there  is  not  more  of  either  than  the  mixture  will 
afterwards  retain  when  cold.  Tincture  of  benzoin,  tolu,  and 
other  gum-resin  tinctures,  should  be  added  to  mixtures  nearly  at 
