Am.  Jour.  Pharm. 
Feb.,  1884. 
Solubility  of  Calcic  Hydrate. 
113 
ture  of  a  shop  will  rise  above  32°0.  (90°F.),  and  yet  at  that  point 
water  holds  in  solution  about  0*5  gr.  CaO  per  fluidounce. 
Neither  can  we  account  for  these  faulty  waters  on  the  hypothesis 
that  undistilled  water  had  been  used  in  their  preparation,  unless, 
indeed,  the  water  had  been  altogether  exceptional  in  permanent  hard- 
ness. I  have  found  that  a  water  containing  about  10  grains  of  total 
solids  per  gallon  gives  lime  water  of  full  strength.  At  the  same  time 
this  does  not  alter  the  fact  that  only  distilled  water  should  be  employed 
in  preparing  liquor  calcis. 
Other  two  hypotheses  remain,  either  of  which  would  furnish  a  suf- 
ficient cause  for  even  the  weakest  lime  water.  One  is  that  the  calcic 
hydrate,  not  having  been  properly  stored,  had  almost  entirely  changed 
its  constitution  and  become  carbonate;  the  other,  that  the  solution, 
after  decantation  or  filtration,  had  been  so  badly  kept  that  the  lime 
originally  present  had  all  or  nearly  all  been  precipitated.  It  is  a  well- 
known  fact,  and  one  which  is  daily  made  use  of  by  the  agriculturist 
in  the  application  of  lime  to  the  soil,  that  if  burnt  lime  be  exposed  to 
the  atmosphere,  even  for  a  very  short  time,  it  passes  over  into  the 
milder  form  of  carbonate.  The  same  reaction,  of  course,  takes  place 
on  the  shop  shelves,  and  if  slaked  lime  is  not  kept  in  an  air-tight 
vessel,  it  necessarily  follows  that  it  will  deteriorate,  owing  to  the 
absorption  of  0O2.  If,  forgetting  this,  any  pharmacist  has  been  care- 
less in  storing  the  slaked  lime,  it  need  not  be  wondered  at  if  his  lime 
water  is  weak. 
I  have  found  that  lime  water  can  be  made  of  full  strength  with 
calcic  hydrate,  mixed  with  15  per  cent,  of  carbonate;  with  equal  parts 
of  hydrate  and  carbonate  I  obtained  0*5  gr.  CaO  per  fluidounce ;  with 
25  per  cent,  hydrate  and  75  carbonate,  0*4  gr. ;  and  with  10  per  cent, 
hydrate  and  90  carbonate,  the  amount  dissolved  was  only  0*1  grain. 
It  is  stated  in  almost  every  text-book  that  calcic  carbonate  is  insol- 
uble in  water,  and  if  this  is  so  these  results  are,  to  say  the  least,  very 
singular.  I  have  been  able,  however,  to  find  several  authorities  who 
differ  from  the  popular  belief.  Among  others,  Thorpe1  states  that  a 
litre  of  water  dissolves  0*1  gram  Ca0O3,  that  is  in  the  proportion  of 
10,000  to  1.  My  own  experiments  go  to  prove  that  40,000  to  1  is 
nearer  the  mark,  but  whatever  the  solubility  is  it  is  quite  appreciable, 
and  the  alkalinity  can  readily  be  estimated. 
1  "Inorganic  Chemistry,"  vol.  1,  p.  107. 
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