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STRENGTH  OF  DILUTED  ACETIC  ACID. 
ON  THE  STRENGTH  OF  DILUTED  ACETIO  ACID, 
By  John  M.  Maisch. 
The  diluted  acetic  acid  enters  into  a  number  of  pharmaceuti- 
cal preparations,  particularly  such  as  are  intended  for  internal 
use,  as  syrups,  oxymels,  acetate  of  ammonia,  and  various  others  ; 
it  is,  therefore,  of  some  importance  to  obtain  it  always  of  a  cer- 
tain strength,  though  in  the  dilute  state  in  which  it  is  given, 
some  variation  may  in  many  cases  be  of  little  or  no  consequence. 
The  questions  to  be  answered  consequently  are:  How  strong  is 
this  acid  to  be  ?  Which  of  the  properties  required  by  our  Phar- 
macopoeia is  indicative  of  its  intended  strength  ?  And  which  is 
the  proportion  of  the  acetic  acid  and  distilled  water,  in  order  to 
obtain  the  desired  product  ? 
The  Pharmacopoeia  requires  the  dilute  acetic  acid  to  have  a 
specific  gravit}^  of  1.004,  which,  according  to  Mohr's  tables,  indi- 
cates 3  per  cent,  of  the  monohydrated  acetic  acid  HO,  C4  H3  03; 
the  weight  of  equivalent  of  this  monohydrate  is  60,  that  of  bicar- 
bonate of  potassa  HO,  KO,  2C02  100.2,  therefore  100  grains  of 
this  acid  are  sufficient  to  saturate  ~~==5_.Q1  gr.  of  that  bicar- 
bonate, while  the  Pharmacopoeia  requires  7.5  grs.  to  saturate 
100  grs.  of  the  dilute  acid.  But  7.5  grs.  of  the  bicarbonate  of 
potassa  will  saturate  ^=4.5  grs.  of  the  monohydrated  acid,  or 
100  grs.  of  an  acid  of  4.5  per  cent.,  which  shows  a  difference  of 
1.5  per  cent,  between  the  power  of  saturation  and  the  strength 
as  indicated  by  specific  gravity. 
This  difference  cannot  be  decided  by  the  product  obtained  by 
the  formula  of  the  Pharmacopoeia,  which  again  furnishes  an 
acid  differing  in  strength  from  both.  On  mixing  acetic  acid  with 
distilled  water,  a  contraction  invariably  occurs,  and  the  sp.  grav- 
of  the  mixture  is  higher  than  it  is  calculated,  from  the  propor- 
tion of  the  articles  used  ;  this  difference,  however,  becomes  more 
insignificant  as  the  dilution  increases. 
The  Dublin  Pharmacopoeia  uses  the  same  proportion  as  the 
U.  S.  P. ;  but  it  employs  an  acid  of  1.044  spec,  grav.,  or  33  pr. 
ct.,  and  states  the  diluted  acid  to  be  1.006.  By  calculation  the 
sp.  grav.  is  found  to  be  7±H^  =1.0055,  (4  per.  ct.  acid  of  Mohr's 
table,)  and  the  percentage ss*™^  =4.283 ;  by  the  contraction  the 
