PURE  CARBONIC  ACID,  MINERAL  AND  LITHIA  WATER.  115 
and  delicate  class  of  manipulations.  Space  will  here  allow  only 
more  particular  allusion  to  the  difficulties  encountered  in  the 
preparation  and  purification  of  one  of  the  most  essential  ingre- 
dients, the  carbonic  acid.  The  materials  generally  used  are  oil 
of  vitriol  and  ground  limestone.  Contaminations,  derived  both 
mechanically  and  chemically  from  both  of  these,  are  almost  in- 
variably imparted  to  the  gas. 
Mechanically  (in  the  form  of  infinitesimal  spray)  may  be  car- 
ried over  sulphates  of  lime,  magnesia  and  iron,  with  the  sulphuric 
acid  itself,  and  lead  and  sometimes  arsenic  contained  therein ;  while 
chemically  there  may  pass  over  sulphurous  acid  (from  the  oil  of 
vitriol,)  sulphuretted  hydrogen  (from  pyrites  and  other  metallic 
sulphurets  in  the  limestone,)  and  frequently,  also,  the  limestone 
evolves,  under  the  action  of  the  acid,  bituminous  and  nitrogenous 
organic  vapors  of  nauseous  odors  and  savors.  What  wonder 
that  the  opinion  should  be  prevalent,  even  among  those  accus- 
tomed to  natural  carbonic  acid  waters,  that  plain  "  Soda  Water," 
as  found  in  the  shops,  must  necessarily  be  a  nauseous  dose,  only 
made  palatable  by  disguising  it  with  syrups,  essences,  etc. 
Let  no  captious  Rip  van  Winkle,  adherent  to  the  hermetical 
lore  of  our  grandsires,  aver  that  these  minute  impurities  are  the- 
rapeutically nugatory.  Such  a  one,  to  be  consistent,  must  re- 
pudiate such  waters  altogether,  both  natural  and  artificial,  for — 
without  going  to  the  same  absurd  extreme  as  Hahnemann's  dis- 
ciples— we  cannot,  at  the  present  day,  deny  that  the  frequent  repeti- 
tion of  minute,  though  still  chemically  appreciable,  doses  of  powerful 
medicaments,  will  usually  produce  in  time  a  greater  or  less  cumu- 
lative effect. 
Even  if  these  initial  difficulties  have  been  conquered,  as  they 
usually  are  not,  the  storage  and  preservation  in  quantity  of  car- 
bonic acid  water  presents  a  new  class  of  obstacles.  Reservoirs 
for  the  purpose  must  have  the  difficultly  compatible  qualifications 
of  infrangibility,  both  by  pressure  and  percussion,  cheapness  and 
total  resistance  to  the  solvent  power  of  the  acid  liquid.  No  metal 
combines  these,  except  possibly  tin  of  chemical  purity  (an  article 
not  of  commercial  attainment  at  present,  as  the  best  Banca  tin 
is  contaminated  with  copper,  zinc,  lead  and  arsenic.)  Common 
