250        Pharmacy  of  Calcium  Glycerophosphate.    {  AJul°nr^javm' 
The  influence  of  sodium  citrate  upon  the  solubility  was  roughly 
determined.  It  was  found  that  an  admixture  of  20  per  cent,  of  this 
salt  increased  the  solubility  from  1  :  57  to  1 : 32  and  that  the  solubility 
of  calcium  glycerophosphate  in  a  1  : 250  solution  of  sodium  citrate 
was  1:41.  Both  of  these  solutions  quickly  precipitated  calcium 
citrate. 
Summary. 
It  has  been  shown  that, 
1.  The  solubility  in  water  of  calcium  glycerophosphate  is  in- 
creased by  acids  and  by  sodium  citrate. 
2.  The  solubility  in  water  is  repressed  by  alcohol,  glycerin,  and 
sodium  glycerophosphate  solution. 
3.  Lactic,  citric,  and  phosphoric  acids  increase  the  solubility  in 
presence  of  alcohol  or  glycerin  or  both. 
4.  Acids  hasten  the  hydrolysis  of  the  salt-producing  precipitates 
except  that  lactic  acid  tends  to  keep  the  hydrolytic  products  in 
solution. 
5.  Alcohol  and  glycerin  repress  the  hydrolysis  even  in  the  pres- 
ence of  acids. 
6.  In  the  N.  F.  formula  for  the  compound  elixir  the  lactic  acid 
should  be  increased  to  at  least  40  mils,  and  in  the  formula  for  the 
calcium  and  sodium  glycerophosphate  elixir  the  phosphoric  acid 
should  be  replaced  by  at  least  20  mils  of  lactic  acid. 
Discussion. 
The  use  of  various  acids  in  order  to  increase  the  solubility  of 
calcium  glycerophosphate  so  that  an  effective  amount  of  it  may  be 
presented  in  the  old-time  teaspoonful  dose,  while  highly  necessary 
for  pharmaceutical  reasons,  is,  nevertheless,  quite  undesirable  from 
chemical  considerations.  The  addition  of  acid  causes  the  formation 
of  free  glycerophosphoric  acid,  which  undergoes  autohydrolysis,3 
the  free  hydroxyls  of  the  acid  acting  as  the  catalyst,  so  that,  even- 
tually, the  mixture  consists  of  a  calcium  salt,  free  added  acid, 
glycerin,  and  phosphoric  acid.  There  may  then  be  little  or  no  true 
glycerophosphates  in  the  solution.  Not  only  will  this  occur  with  the 
calcium  salt  but  it  will  obtain  with  all  glycerophosphates  in  acid 
solution.  Self4  suggested  the  addition  of  sulphuric  acid  in  making 
acid  glycerophosphates  and  DuBois1  states  that  these  compounds  are 
3  Malengreu  and  Prigent,  Zeit.  physiol.  Chem.  (1911),  73-  68-84. 
4  Pharm.  Jour.,  May  16,  1908,  p.  627. 
