468  Barium  Phosphates  in  Acidimetry.  {Am/eXi88h7arm 
the  glycerol  was  obtained  as  nitroglycerol,  and  weighed  in  this  form, 
but  this  and  other  methods  are  also  liable  to  error.    The  present 
method  is  one  in  which  the  compounds  of  glycerol  with  benzoyl  are 
weighed.    There  are  three  benzoates  of  glycerol,  according  as  to 
whether  one,  two,  or  three  atoms  of  the  hydrogen  of  the  latter  are 
replaced  by  the  group  C7H502.    The  following  gives  the  method  of 
procedure  : — Glycerol  was  diluted  to  a  known  extent  with  water  (0*1 
gm.  in  10  or  20  c.c.) ;  5  c.c.  of  benzoic  chloride  and  35  c.c.  of  sodium 
hydroxide  added ;  this  mixture  was  cooled  and  shaken  for  ten  or  fif- 
teen minutes.    The  benzoyl  compound  which  separated  was  collected 
on  a  weighed  filter,  washed  with  water,  dried  at  100°,  and  weighed. 
A  mean  of  eight  estimations  gave  the  amount  of  the  compound  as 
0*385  gm.    In  a  second  series  of  four  estimations,  the  number  ob- 
tained was  rather  higher,  the  mean  being  0*395  gm.  ;  in  these  cases 
the  alkaline  filtrate  was  shaken  a  second  time  with  benzoic  chloride 
and  sodium  hydroxide ;  the  second  filtrate  contained  hardly  a  trace  of 
glycerol.    These  numbers  formed  a  basis  for  the  subsequent  analyses, 
and  showed  that  the  compound  formed  in  this  way  was  chiefly  the  tri- 
benzoate;  theoretically  the  amount  of  that  compound  for  0*1  gm.  of 
glycerol  would  be  0.439  gm.    Tables  of  the  amount  of  glycerol  in 
various  forms  of  beer  and  wine,  estimated  by  this  method,  are  given, 
the  numbers  obtained  being  somewhat  less  than  those  given  by  Borg- 
mann.    The  method  has  the  following  advantages :  The  substance 
weighed  is  solid  and  not  hygroscopic,  and  admixture  with  inorganic 
and  nitrogenous  substances  is  avoided. 
BARIUM  PHOSPHATES— THEIR  APPLICATION  IJST 
ACIDIMETRY.1 
By  A.  Villiees. 
Phosphoric  acid  is  bibasic  when  phenolphthalein  is  used  an  an  indi- 
cator, and  can  be  titrated  with  a  solution  of  potassium  or  barium  hy- 
droxides. Other  free  acids,  such  as  hydrochloric,  sulphuric,  acetic, 
can  be  titrated  in  presence  of  phosphoric  acid  by  means  of  potassium 
hydroxide,  but  not  with  baryta. 
Joly  has  already  shown  that  when  barium  chloride  is  added  to  diso- 
Compt.  rend.,  civ.,  1104-1106.  Eeprinted  from  Jour.  Chem.Soc,  August,  p.  701. 
