Are*bi0uYrVTi8a99m*}      Lithium  Benzoate  and  Salicylate.  61 
above  residue  should  not  be  affected  by  the  addition  of  a  little 
sodium  cobaltic  nitrite  solution  (limit  of  potassium). 
All  the  other  tests,  excepting  that  for  chloride,  could  be  applied 
to  this  solution,  or  an  aqueous  solution  of  the  salt  itself  could  be 
employed.  This  solution  (1-25)  should  not  be  affected  by  hydro- 
gen sulphide  or  ammonium  oxalate,  and  should  not  produce  more 
than  a  slight  coloration  with  ammonium  sulphide. 
If  0-5  gramme  of  the  salt  is  dissolved  in  25  c.c.  of  a  mixture,  con- 
sisting of  10  parts  of  water  and  15  parts  of  alcohol,  then  acidulated 
with  nitric  acid,  the  resulting  solution  should  not  produce  more 
than  a  slight  opalescence  on  the  addition  of  a  few  drops  of  silver 
nitrate  solution  (limit  of  chloride). 
The  method  of  ignition  and  subsequent  titration  for  estimating 
the  per  cent,  of  pure  salt,  as  per  the  U.S.P.,  has  not  given  me  satis- 
factory results.  The  results  were  non-concordant,  and  the  time  re- 
quired for  bringing  about  complete  solution  of  the  ignited  residue 
was  all  out  of  proportion  to  that  allotted  the  ordinary  analyst.  I 
have  allowed  the  solvent  to  act  for  forty-eight  hours,  with  frequent 
agitation,  and  yet,  in  some  cases,  solution  was  incomplete.  The 
ignited  residue  becomes  so  hard  and  adheres  so  firmly  to  the  porce- 
lain vessel,  that  it  almost  appears  to  form  part  of  the  vessel.  I 
tried  ignition  at  higher  and  lower  temperatures,  hoping  thus  to 
overcome  the  above  difficulty,  but  without  success. 
After  spending  some  time  and  sacrificing  a  number  of  porcelain 
dishes,  I  happily  thought  of  a  method  that  proved  to  be  very  satis- 
factory. It  is  as  follows :  Weigh  about  0-5  gramme  of  the  dry 
lithium  benzoate  into  a  platinum  capsule,  add  2  grammes  of  pure, 
dry,  ammonium  sulphate,  mix  well  with  a  platinum  wire  and  ignite. 
Apply  the  flame  gradually  at  first,  so  as  to  avoid  any  possible  spurt- 
ing. The  residue  is  lithium  sulphate.  From  this  the  amount  of 
pure  lithium  benzoate  can  easily  be  calculated. 
One  gramme  of  pure,  dry  lithium  benzoate  yields  0-43  of  a  gramme 
of  lithium  sulphate,  or  the  amount  of  lithium  sulphate  multiplied 
by  2-3256  gives  the  amount  of  pure  lithium  benzoate  in  the  sam- 
ple under  examination. 
The  above  method  can  be  readily  and  quickly  applied,  and  the 
results  are  concordant.  An  estimation  can  easily  be  made  in  twenty 
minutes.  I  have  made  them  in  ten  minutes.  As  soon  as  the 
ammonium  sulphate  begins  to  decompose  the  benzoic  acid  is  liber- 
