jir-M""" }  Volumetric  Analysis.  343 
hydrochloric  acid  must  contain  36'5  grams  of  the  acid  in  a  liter  of  fluid, 
and  a  normal  solution  of  sodic  hydrate,  40  grams. 
In  the  case  of  bivalent  substances,  such  as  lead,  calcium,  oxalic  acid, 
sulphurous  acid,  etc.,  the  equivalent  is  one-half  of  the  atomic  (or  in  the 
case  of  salts,  molecular)  weight  ;  thus  a  normal  solution  of  oxalic  acid 
would  contain        or  63  grams  of  the  acid  in  a  liter  of  fluid. 
Further,  in  the  case  of  trivalent  substances,  such  as  phosphoric  acid, 
a  normal  solution  of  sodic  phosphate  would  be  made  by  dissolving 
=  119*3  grants  of  the  salt  in  distilled  water,  and  diluting  the  liquid  to 
the  measure  of  one  liter. 
The  following  standard  test  solutions  have  been  recommended  to  be 
introduced  into  the  United  States  Pharmacopoeia,  the  same  being  now 
official  in  the  British  Pharmacopoeia  : 
1 .  Volumetric  Solution  of  Bichromate  of  Potassium, 
(K,CrA  =  295). 
This  is  a  decinormal  solution,  and  contains  4*9 17  grams  of  the  salt 
in  one  liter  of  the  liquid. 
The  reaction  which  takes  place  between  potassic  bichromate  and 
ferrous  oxide  is  as  follows  : 
eFeO  +  K^CrPy  =  3Fe203+Cr203+K20. 
It  is  therefore  necessary  that  one-sixth  of  an  equivalent  in  grams 
should  be  used  in  a  liter  for  the  normal  solution,  and  one-sixtieth  for  the 
decinormal ;  and  as  it  is  preferable  on  many  accounts  to  use  a  dilute 
solution,  the  latter  is  the  more  convenient  for  general  purposes. 
2.  Volumetric  Solution  of  Hyposulphite  of  Sodium. 
Na2S203,  5H0O  =  248. 
The  normal  solution  contains  248  grams  in  the  liter  ;  the  decinor- 
mal solution  is  usually  more  convenient,  and  contains  one-tenth  as 
much,  or  24*8  grams  in  the  liter,  while  in  some  cases  the  centinormal 
solution  is  desirable.  This  can  readily  be  prepared  by  diluting  100 
fluigrams  of  the  decinormal  solution  to  one  liter. 
3.  Volumetric  Solntion  of  Iodine.     I  =  127. 
The  solution  directed  in  the  Pharmacopoeia  is  the  decinormal  solu- 
tion, which  contains  12*7  grams  of  iodine  in  the  liter. 
4.  Volumetric  Solution  of  Nitrate  of  Silver, 
Ag.N03=  170. 
This  solution  is  also  the  decinormal  solution,  and  contains  17  grams 
of  nitrate  of  silver  (corresponding  to  io*8  grams  of  pure  silver)  in  one 
liter  of  liquid. 
