Am.  Jour.  Pharm. j       AsSd\>  PvOCCSSCS   of   U S .P .  IX.  II" 
March,  1917      }  J  j 
With  volatile  organic  salts,  such  as  ammonium  benzoate  and  sali- 
cylate, the  above  method  would  not  apply.  The  method  used  for 
these  salts  is  as  follows  :  To  .5  gram  of  the  salt,  dissolved  in  10 
mils  of  water,  are  added  5  mils  of  diluted  sulphuric  acid.  The 
liberated  organic  acids  are  then  extracted  with  successive  portions 
of  25,  15  and  10  mils  of  chloroform.  The  chloroform  solution  is 
evaporated  spontaneously,  25  mils  of  neutral  alcohol  are  added,  and 
the  solution  titrated  with  n  10  barium  hydroxide. 
Gravimetric  Methods. 
There  are  quite  a  number  of  purely  gravimetric  methods  in  the 
U.  S.  P.  processes.  They  may  be  divided  into  four  classes :  First, 
decomposition  directly  by  heat  into  definite  compounds,  admitting  of 
weighing  and  determination ;  secondly,  precipitation  ;  thirdly,  pre- 
cipitation and  further  decomposition  of  the  precipitate  by  heat; 
fourthly,  miscellaneous. 
The  following  substances  are  assayed  by  the  first  method :  cal- 
cium glycerophosphate  and  all  the  official  bismuth  compounds,  con- 
sisting of  bismuth  and  ammonium  citrate,  betanaphtholate,  hydrox- 
ide, subcarbonate,  subgallate,  subsalicylate,  and  the  subnitrate. 
The  inorganic  bismuth  compounds  are  simply  incinerated ;  but  in 
the  case  of  the  organic  bismuth  compounds  nitric  acid  is  added  to 
completely  destroy  any  remaining  carbon,  the  solution  evaporated 
to  dryness  and  ignited,  and  calculated  as  Bi203.  Under  bismuth 
betanaphtholate,  a  method  is  also  given  to  determine  the  amount  of 
of  betanaphthol  present,  as  follows  :  To  the  salt,  10  mils  of  HC1  are 
added,  and  the  betanaphthol  is  extracted  by  successive  portions  of 
chloroform.  The  chloroform  solution  is  evaporated.  The  residue 
should  not  weigh  less  than  15  per  cent,  of  the  salt  taken. 
Calcium  glycerophosphate  is  assayed  by  dissolving  in  water,  add- 
ing acetic  acid,  and  then  ammonium  oxalate.  The  calcium  oxalate 
is  washed,  dried  and  ignited,  and  from  the  weight  of  calcium  oxide 
found,  the  glycerophosphate  is  calculated. 
The  second  gravimetric  method  of  assay,  precipitation,  is  used 
for  the  following :  ammoniated  mercury  and  bichloride.  For  ex- 
ample, .5  Gm.  of  mercuric  chloride  is  dissolved  in  water  and  acidu- 
lated with  HC1,  and  completely  precipitated  by  H2S.  The  precipi- 
tate is  filtered  upon  counterpoised  filters  and  washed,  first  with 
water,  then  with  three  portions  of  10  mils  of  alcohol.  The  funnel 
is  closed  with  a  stopper,  and  to  remove  any  adhering  sulphur  surfi- 
