Am.jour.  Pharm.j  Contributions  from  the  School  of  Pharmacy,  etc.  535 
tion  of  precipitates,  what  proportion  of  the  phosphoric  acids  must  be 
neutralized  by  alkalies  in  order  to  cause  the  precipitates  ? 
All  the  metallic  salts  and  all  the  acids  were  obtained  and  used  in 
solutions  of  known  strength. 
The  orthophosphoric  acid  was  prepared  by  the  first  process  of  the 
U.  S.  u  Pharmacopoeia "  for  the  diluted  acid,  and  was  used  of  the 
strength  of  that  preparation,  near  10  per  cent,  of  acid.  1 
For  the  pyrophosphoric  acid,  ordinary  sodium  phosphate  was  fused 
to  pyrophosphate  ;  the  solution  of  the  latter  precipitated  by  lead  acetate 
solution,  and  the  washed  precipitate  transposed  with  hydrogen  sulphide. 
The  filtrate  was  freed  from  gas  by  evaporation  in  vacuo  at  ordinary 
temperature.  The  solution  was  found  free  from  sodium  salt  and  from 
extraneous  acids.    One  cc.  contained  0*0608  gram  of  the  acid. 
The  metaphosphoric  acid  was  prepared  by  evaporating  the  solution 
of  orthophosphoric  acid  to  dryness  and  gently  igniting  the  residue.  Of 
this,  10*550  grams  were  dissolved  in  300  cc.  of  water,  or  0*035  grams 
of  acid  to  one  cc.  of  water.  Heat  was  avoided  in  dissolving,  and  the 
solution  was  used  fresh. 
Solutions  of  the  following  metallic  salts  were  prepared,  each  in  three 
degrees  of  strength,  5  per  cent.,  1  per  cent,  and  J  per  cent. 
Barium  chloride,  absolute ; 
Calcium  chloride,  absolute  ; 
Magnesium  sulphate,  cryst. ; 
Aluminium  sulphate,  cryst. ; 
Ferric  chloride,  absolute ; 
Tincture  of  chloride  of  iron  ; 
Ferrous  chloride,  absolute  5 
Ferrous  sulphate,  cryst.  5 
Lead  nitrate,  cryst. ; 
Lead  acetate,  cryst. ; 
Silver  nitrate,  cryst. 
The  nitric  acid  used  for  dissolving  precipitates  was  35  per  cent,  of 
hydrogen  nitrate ;  the  hydrochloric  acid,  24  per  cent.  ;  and  the  soda 
solution  used  to  neutralize  phosphoric  acid  and  produce  precipitates  was 
7  per  cent,  of  sodium  oxide. 
Another  solution  of  same  strength  was  prepared  from  common  sodium  phosphate 
by  precipitation  with  lead  acetate,  and  decomposition  of  the  lead  phosphate  with 
hydrogen  sulphide,  the  filtrate  being  freed  from  the  gas.  This  solution  was  found 
to  have  a  trace  of  sulphuric  acid  from  contamination  of  the  sodium  phosphate  with 
sulphate  ;  the  testing  of  this  salt  having  been  neglected  until  the  preparation  was 
completed.    The  process  worked  well. 
