50 
ON  EFFERVESCING  POWDERS. 
from  which  tartaric  acid  precipitates  cream  of  tartar.  Some- 
times, especially  in  France,  where  such  formula  have  originated 
and  were  published,  the  Rochelle  salt  is  partly  or  wholly  re- 
placed by  sulphate  of  soda,  and  sulphate  of  magnesia,  and  the 
powders  thus  prepared  indiscriminately  sold  under  the  name  of 
"poudre  de  Sedlitz,"  from  which  they  chiefly  differ  by  their 
bitter  taste,  the  aperient  properties  being  about  alike.  If  these 
powders  are  put  up  in  an  air-dry  state,  they  keep  admirably 
well  for  any  length  of  time.  Of  the  British  Pharmacopoeias,  the 
Edinburgh  and  Dublin  give  directions  for  similar  preparations 
under  the  name  of  pulveres  effervescentes,  for  which  either  bi- 
carbonate of  soda  or  potassa  may  be  used.  The  Dublin  Phar- 
macopoeia also  directs  pulveres  effervescentes  citrati,  which  are 
made  of  citric,  instead  of  tartaric  acid.  Under  the  name  of 
simple  effervescing  or  Seltzer  powder,  Dorvault  directs  4  gram- 
mes (61.7  grs.)  of  bicarbonate  of  soda  in  a  blue,  and  the  same 
quantity  of  tartaric  acid  in  a  white  paper,  which,  when  dissolved 
in  a  wine  bottle  full  of  water  containing  1|  or  2  oz.  of  syrup  of 
currants  or  lemon,  form  a  very  refreshing  drink.  There  are 
many  similar  formulae  for  "effervescing  lemonade,"  usually  con- 
sisting of  bicarbonate  of  soda,  which  for  its  cheapness  is  pre- 
ferred to  the  potassa  salt,  mixed,  with  a  certain  quantity  of 
sugar,  flavored  with  oil  of  lemon  in  one  paper,  and  of  tartaric 
or  citric  acid  done  up  in  another  one.  The  chief  object  in  ma- 
king such  powders  is  to  obtain  their  refrigerant  qualities,  and 
the  acid  is  therefore  taken  somewhat  in  excess  to  assure  of  the 
entire  decomposition  of  the  carbonate  and  to  procure  a  quantity 
of  an  acid  salt,  either  bitartrate  or  bicitrate,  which  by  its  agree- 
able acidulous  taste  adds  much  to  the  pleasant  and  refreshing 
properties.  Sometimes,  however,  the  physician  desires  an  ant- 
acid effect  at  the  same  time  with  the  refrigerant  action  of  the 
carbonic  acid,  and  increases  the  quantity  of  the  alkaline  carbo- 
nate sometimes  far  beyond  the  power  of  saturation  of  the  acid 
employed. 
An  effervescing  powder  is  also  occasionally  made,  consisting 
of  bicarbonate  of  ammonia,  and  of  citric  acid,  and  thus  forms  a 
pleasant  substitute  for  the  solution  of  citrate  of  ammonia  of  the 
London  College,  in  as  much  as  with  each  dose  beside  the  am- 
monia, a  corresponding  quantity  of  carbonic  acid  is  administered 
