ArAJgust5mm*}    Hypophosphorous  Acid  and  Hypophosphites.  389 
nation  i.  e.  the  quantity  of  NaOH  necessary  to  decompose  the  ferric 
hypophosphite  (see  determination  of  ferric  oxide).  To  obtain  the 
number  of  cc.  of  NaOH  corresponding  to  the  ferric  hypophosphite, 
there  must  be  subtracted  from  the  cc.  NaOH  required  to  indicate  an 
alkaline  reaction  after  oxidation,  the  correction  due  to  the  bromine  and 
the  number  of  cc.  NaOH  necessary  to  precipitate  the  ferric  oxide 
from  the  ferric  hypophosphite  taken.  One  other  precaution  must  be 
observed  with  this  salt,  it  is  best  obtained  in  solution  by  using  10  cc« 
water  with  sufficient  bromine,  applying  slight  heat  and  agitating  well 
until  dissolved,  then  diluting  with  water  to  100  cc.  and  boiliug  as 
with  the  soluble  salts. 
The  results  of  these  determinations  were  always  calculated  as  the 
hypophosphite  of  the  metal  taken,  and  if  after  the  determination  of 
the  impurities  the  figures  fell  short  of  100,  the  determination  of 
phosphoric  acid  (after  oxidation)  was  undertaken  so  as  to  estimate  the 
quantity  of  phosphite  by  the  method  given  on  page  327.  Regarding 
the  qualitative  test  for  phosphite  mentioned  on  page  326,  an  unfavor- 
able opinion  previously  formed  was  strengthened,  as  a  sample  con- 
taining quantitatively  13'34  per  cent,  phosphite  gave  no  precipitate 
with  the  test,  and  a  sample  of  hypophosphorous  acid,  free  from  phos- 
phorous acid,  but  containing  sulphuric  acid  giving  a  heavy  precipitate. 
Water  determination,  by  drying  about  two  gm.  at  120°  C. 
Sulphuric  acid  determination,  by  use  of  BaCl2  and  HC1. 
Hydrochloric  acid  determination  presents  some  difficulties  in  the  pres- 
ence of  hypophosphites  owing  to  the  reduction  of  silver  nitrate  by  the 
latter.  It  can  be  detected  and  estimated  by  dissolving  the  salt  in  nitric 
acid,sp.  gr.  1*20,  and  adding  AgN03  until  a  dark  coloration  sets  in,  stir- 
ring actively  to  coagulate  the  precipitate,  adding  a  little  more  silver  ni- 
trate and,  after  coagulating  the  precipitate,  diluting  with  water  and 
filtering  through  a  small  plug  of  absorbent  cotton.  The  precipitate  is 
well  washed  and  the  AgCl  dissolved  out  by  pouring  ammonium 
hydrate  through  the  cotton  and  re-precipitated  by  adding  nitric  acid 
to  the  filtrate. 
Carbonic  acid  determination,  qualitatively  by  effervescence  on  addi- 
tion of  a  stronger  acid,  quantitatively  by  addition  of  a  known  excess 
of  normal  oxalic  acid,  boiling  and  titrating  the  excess  of  oxalic  acid; 
the  deficiency  of  NaOH  is  calculated  as  carbonate. 
Phosphoric  acid  is  determined  in  soluble  hypophosphites  by  warm- 
ing with  HC1  to  decompose  any  carbonate  that  may  be  present,  adding 
