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STRENGTH  OF  DILUTED  ACETIC  ACID.  807 
spec.  grav.  is  slightly  increased.  The  acid  of  the  U.  S.  P.  weighs 
1.041,  and  shows  its  percentage  of  monohydrate  =  31.  The 
percentage  of  the  mixture  must  therefore  be  31xL041  =4.013,  while 
the  spec.  grav.  is  found  to  be  _^=1.0051,  which  certainly  cannot 
be  much  out  of  the  way.  In  round  numbers,  therefore,  the  for- 
mula of  the  Pharmacopoeia  furnishes  a  preparation  of  four  per 
cent,  of  HO,  C4  H3  03,  so  that  100  grains  of  it  must  saturate 
4xlQQ-2==6.67  gr.  bicarbonate  of  potassa.  If,  on  the  other  hand, 
a  dilute  acid  is  wanted,  which  shall  not  contain  but  three  per 
cent,  of  the  monohydrate,  the  proportion  of  the  acid  and  water 
must  be  1:  9.75;  for  31xl-041=I2.99  per  cent.,  and  12^=1.0038 
7  10.791         >         r  7  10.75 
spec.  grav.  The  specific  gravity  of  an  acid  of  3  per  cent,  is 
1.004  according  to  Mohr. 
A  fluidounce  of  water  has  a  weight  of  455.694  grains;  there- 
fore a  fluidounce  of  acetic  acid  of  1.041  spec.  grav.  equals  the 
weight  of  474.388  grs.  Troy,  and  such  an  acid  containing  31 
per  cent.  HO,  C4  H3  03,  its  fluidounce  must  contain  147.06  grs. 
of  the  monohydrate,  which,  by  the  formula  of  the  Pharmacopoeia, 
is  divided  among  8  fluidounces,  each  of  which  will  contain  147-06 
=  18.38  grs.  HO,  C4H3  03,  which  saturate  30.699  grains, 
HO,  KO,  2C02  and  55.30  grs.  CaO,  C02.  If,  however,  the 
intended  strength  of  the  diluted  acid  was  to  be  3  per  cent,  the 
147.06  grs,  of  the  monohydrated  acid  would  be  divided  among 
lOf  fluidounces,  thus  leaving  for  1  fluidounce  but  13.68  grs. 
monohydrate,  which  are  saturated  by  22.86  grs.  bicarbonate  of 
potassa,  or  11.41  grs.  pure  carbonate  of  lime. 
For  preparations  where  the  dilute  acetic  acid  acts  merely  as 
a  preventive  agent,  this  latter  strength  of  3  per  cent,  might 
probably  be  deemed  sufficient ;  but  for  other  preparations,  where 
the  acid  is  of  medicinal  importance,  we  ought  to  rely  on  the  sa- 
turating power  of  the  acid.  To  obtain  one  of  4.5  per  cent, 
strength,  which  would  saturate  for  every  100  grs.  7.5  grs.  of 
bicarbonate  of  potassa,  the  proportions  of  a  31  per  cent,  and 
water  must  be  1 :  6.13  ;  for  =4.5,  and  the  specific  gravity 
of  this  mixture  would  be  7171  =1.0058.    These  proportions  are 
7.13  . 
very  nearly  the  1:6  ;  an  acid  mixed  in  these  proportions  contains 
1.041x31  ^,4,58  per  cent>  HQ.  £4  H3  03,  and  its  specific  gravity 
