m.  Jour.  Pharm.  1 
February,  1904.  J 
Lime  Water. 
67 
as  an  addition  to  bring  about  chemical  change  of  the  more  active 
substances,  as  in  the  well  known  black  or  yellow  washes.  All  of 
these  preparations,  it  will  be  noted,  depend  largely  on  the  fact  that 
the  lime  water  used  be  of  the  full  strength. 
Lime  water  is  official  in  all  known  national  pharmacopoeias,  and 
although  the  official  titles  as  well  as  the  prescribed  modes  of  pre- 
paring the  solution  differ  materially,  the  ultimate  object  that  is 
sought  by  all  is  practically  the  same — a  saturated  solution  of  calcium 
hydrate  in  water,  at  ordinary  temperatures. 
Calcium  hydrate,  as  is  well  known,  varies  considerably  in  its  solu- 
bility, being  much  more  soluble  in  cold  than  in  hot  water,  and  dif- 
fering in  this  respect  from  the  majority  of  chemical  substances.  So 
little  is  known  about  the  physical  or  chemical  changes  that  are  pro- 
duced by  the  solution  of  chemical  substances,  in  water,  that  it  would 
be  futile  to  attempt,  at  this  time,  a  general  discussion  of  the  under- 
lying principles  or  factors  that  regulate  the  solution  of  calcium 
hydrate.  The  subject  has  been  investigated  in  a  practical  way  by 
several  persons,  among  them  M.  A.  Lamey  {Comptes  Rendus,  Feb- 
ruary, 1878,  page  333),  L.  C.  W.  Cocx  {Arch.  f.  Phar.,  1879,  page 
145),  and  Thos.  Maben  {Phar.  Jour.,  1883,  reprinted  in  A.  J.  P.,  1884, 
page  1 10). 
The  United  States  Pharmacopoeia  of  1890  defines  liquor  calcis  as 
"a  saturated  aqueous  solution  of  calcium  hydrate,"  and  gives  among 
other  tests  one  for  the  quantitative  estimation  of  the  contained 
alkali.  The  Pharmacopoeia  does  not,  however,  limit  the  allowable 
variation  of  the  calcium  hydrate  in  solution,  but  simply  states  that 
50  c.c.  of  the  official  solution  should  require  for  complete  neutrali- 
zation about  20  c.c.  of  oxalic  acid,  decinormal  volumetric  solution, 
corresponding  to  about  0148  per  cent,  of  calcium  hydrate. 
The  German  Pharmacopoeia,  on  the  other  hand,  directs  that  lime 
water  should  contain  from  0-148  to  0-167  Per  cent-  of  calcium 
hydrate,  while  the  other  requirements  are  practically  the  same  as 
those  of  the  U.S.P. 
Just  a  word  here  as  to  the  applicability  of  these  two  quantitative 
methods,  from  a  practical  point  of  view. 
The  German  Pharmacopoeia  directs  the  use  of  a  normal  volumetric 
hydrochloric  acid  solution.  This,  in  addition  to  the  added  difficulty 
of  making  the  solution,  has  the  objection  of  being  unduly  concen- 
trated ;  100  c.c.  of  lime  water  requiring  only  4  0  to  4-5  c.c.  of  normal 
hydrochloric  acid  for  complete  neutralization. 
