462      Hypophosphorous  Acid  and  Hypophosphites.  {Am'septr,'i889arm' 
ensure  a  fifty  per  cent,  acid ;  that  the  acid  was  not  tested  volumetrically 
before  being  placed  upon  the  market,  as  this  test  would  reveal  the 
amount  of  free  acid ;  and  that  the  quality  of  the  acid  has  not  much 
improved  since  Mr.  Beringer's  publication  in  1882.  Considerable 
has  been  written  regarding  the  presence  of  calcium  oxalate  in  the  acid 
made  by  use  of  oxalic  acid.  With  the  intention  of  ascertaining  the 
amount  present  in  a  50  per  cent,  acid,  and  at  the  same  time  obtaining 
the  specific  gravities  of  the  acid  containing  various  percentages  of  the 
true  hypophosphorous  acid,  a  sample  was  made  from  a  specimen  of 
calcium  hypophosphite  containing  98*48  per  cent.  Ca(H2P02)2.  A 
few  experiments  were  first  made  to  find  the  best  conditions  for  the 
precipitation  of  the  calcium  oxalate ;  using  cold  solutions  of  the  acid 
and  salt,  the  precipitate  was  fine  and  very  difficult  to  wash,  but  if 
boiling  solutions  were  employed  the  precipitate  was  crystalline  and 
easy  to  wash. 
34*5  gm.  Ca(H2P02)2  were  dissolved  in  225  cc.  boiling  water,  and 
to  "this  added  a  solution  of  25*2  gm.  oxalic  acid  in  100  cc.  boiling 
water;  after  boiling  for  one-half  hour  and  allowing  to  cool,  the  mix- 
ture was  filtered  through  a  little  absorbent  cotton  placed  in  the  neck 
of  a  percolator,  and  the  precipitate  thoroughly  washed  with  cold 
water.  The  filtrate  was  evaporated  on  a  water  bath  to  44  grams, 
making  a  sixty  per  cent,  acid;  after  taking  the  specific  gravity  the 
acid  was  diluted  to  fifty  per  cent.,  etc.  The  composition  of  the  fifty 
per  cent,  acid  showed  that  there  was  just  sufficient  material  taken, 
and  no  excess  of  calcium  salt  was  present,  the  neutralization  and  re- 
duction figures  both  being  50  per  cent.,  and  containing  in  addition 
0'97  per  cent.  CaS04  and  0*68  per  cent.  CaC204.  This  amount  of  cal- 
cium oxalate  appears  to  be  the  extreme  limit,  being  made  in  a  boiling 
solution;  but  if  this  quantity  is  sufficient  to  be  injurious  to  health 
may  be  decided  by  more  competent  persons.  The  specific  gravities  of 
the  various  acids  are  given  a  little  later  in  comparison  with  the  same 
strength  acids  made  according  to  the  National  Formulary.  These  spe- 
cific gravities,  differing  so  decidedly  from  my  own  and  those  of  other 
observers,  a  sample  was  prepared  according  to  the  directions  from  41*6 
grams  potassium  hypophosphite  and  60  grams  tartaric  acid.  The 
filtrate  is  intended  to  furnish  a  10  per  cent,  acid;  the  full  yield  with- 
out loss  should  be  264  grams ;  the  quantity  in  this  case  was  223*6 
grams,  a  yield  of  about  85  per  cent.  The  filtrate  was  evaporated  to 
44*72  grams,  corresponding  to  a  50  per  cent,  acid ;  after  taking  the 
