AmAl!gSst,Pi889!m"}    Hypophosphorous  Acid  and  Hypophosphites.  391 
CALCIUM  HYPOPHOSPHITE. 
This  salt  is  directly  or  indirectly  the  source  of  the  officinal  hypo- 
phosphites,  as  well  as  of  the  commercial  acid;  hence  its  purity  is  an 
important  factor  in  considering  the  purity  of  its  preparations.  Four 
I. 
II. 
III. 
IV. 
Ca  (H2P02)2 
99-48  i 
98-27 
98-40 
98-10 
CaS04 
0-55 
1-30 
1-53 
1-59 
CaC03 
Merest  trace. 
0-35 
Trace. 
0-31 
The  insoluble  portion  of  these  samples  was  found  to  consist  of 
carbonate  only,  due  to  the  small  quantity  of  Ca(OH)2  soluble  in 
water  not  having  been  thoroughly  removed,  and  which,  during  evapo- 
ration was  changed  by  atmospheric  carbon  dioxide  into  calcium 
carbonate.  This  is  an  impurity  which  is  so  easily  removed  that  the 
U.  S.  P.  is  right  in  requiring  a  completely  soluble  salt.  A  little  C02 
passed  through  the  nitrate  after  separating  the  excess  of  lime  and 
calcium  phosphate,  boiling  and  filtering  again  is  all  that  is  required; 
there  are  two  nitrations  necessary  in  the  ordinary  method  of  prepara- 
tion, so  the  only  additional  expense  will  be  for  the  C02. 
The  test  for  soluble  phosphate  in  the  U.  S.  P.,  considering  the 
presence  of  sulphate  in  all  samples,  might  give  rise  to  wrong  conclu- 
sions; again,  soluble  phosphate  of  calcium  is  an  acid  salt  and  not 
likely  to  be  found  if  an  excess  of  lime  was  used  in  the  preparation  of 
the  hypophosphite ;  granting  its  presence,  the  requirement  of  forming 
a  neutral  solution,  which  must  not  yield  a  precipitate  on  addition  of 
ammonium  hydrate  to  alkaline  reaction,  is  a  more  appropriate  and 
trustworthy  test  for  phosphate. 
POTASSIUM  HYPOPHOSPHITE. 
Made  by  double  decomposition  between  calcium  hypophosphite  and 
potassium  carbonate.    Two  specimens  were  examined. 
r.  ii.2 
KH2P02,  73-88  98-21 
H20,  1-89  0-49 
KC1,  1-14  0-98 
K2S04,  trace.  0"33 
K2HP03,  13  34 
K2C03,  973 
1  Determined  with  HgCl2  99.48;  with  K2Mn208  99.56  and  with  Br.  99.52. 
2  Ca,  a  trace. 
