THE 
AMERICAN  JOURNAL  OF  PHARMACY. 
SEPTEMBER,  1861. 
ON  THE  CONVERSION  OF  MONOHYDRATED  INTO  COMMON 
PHOSPHORIC  ACID. 
By  J.  M.  Maisch. 
Since  the  investigations  of  Graham  into  the  nature  of  phos- 
phoric acid,  and  his  important  discovery  of  the  three  hydrates, 
which  form  three  corresponding  series  of  salts,  no  further  re- 
searches appear  to  have  been  instituted.  The  standard  w  ^rks 
on  chemistry  contain  scarcely  anything  beyond  an  abstract  of 
the  statements  made  by  Graham  about  thirty  years  ago,  and 
thus  it  happens  that  we  know  very  little  yet  about  the  transition 
of  one  hydrate  into  another  one.  Starting  with  the  phosphate 
of  lime  in  bones  and  the  common  phosphate  of  soda,  the  pyro- 
phosphate of  soda  and  metaphosphoric  acid  have  undoubtedly 
been  often  the  subjects  of  experiments.  What  is  known,  however, 
of  the  reconversion  of  meta-  and  pyrophosphoric  acid  into  the 
ordinary  tribasic  acid,  is  contained  in  the  follov/ing  paragraph 
of  Graham's  Elements  of  Chemistry :  When  solutions  of  the 
metaphosphate  and  pyrophosphate  of  water  are  warmed,  they 
pass  gradually  into  the  state  of  common  phosphate,  combining 
with  an  additional  quantity  of  water  ;  and  the  metaphosphate  of 
water  appears  then  to  become  at  once  common  phosphate  with- 
out passing  through  the  intermediate  state  of  hydration  of  the 
pyrophosphate.  Otto  says,  that  on  boiling  the  solution  of  meta- 
phosphoric acid,  it  is  very  rapidly  converted  into  the  common 
acid,  without,  it  seems,  previously  forming  the  deutohydrate. 
The  glacial  phosphoric  acid  consists  chiefly  of  HOjPO^,  to 
obtain  from  it  the  ordinary  acid,  would  appear  to  require  merely 
to  warm  or  boil  its  aqueous  solution.  On  making  the  experi- 
ment, however,  it  will  not  be  found  so  easy  as  supposed.  The 
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