1 1  o  Basicity  of  the  Phosphorus  Acids.      { A%Ja7;8p76arm' 
limitless  sphere  of  the  nitrogen  and  carbon  compounds.  Phosphorus 
joins  hands,  as  it  were,  with  the  organic  and  protorganic  worlds,  con- 
stituting a  sort  of  connecting  link,  forming  them  into  a  continuous 
series. 
The  acids  of  phosphorus  mark  the  transition  from  the  mineral  to 
the  carbon  acids.  Their  basicity,  for  this  reason,  is  peculiar,  showing 
the  properties  of  both,  and  being  entirely  like  neither.  Organic  or 
carbon  acids  are  compounds  of  oxygenated  hydrocarbon  radicals  with 
hydroxyl.  The  phosphorus  acids  are,  to  a  certain  extent,  analogous 
to  these,  hence  they  may  be  described  as  compounds  of  oxygenated 
hydrophosphorus  radicals  with  hydroxyl.  The  definition,  however,  is 
not  capable  of  general  application,  by  virtue  of  the  fact  that  the  com- 
bined hydrogen  is  wholly  and  completely  typic  in  one  member  of  the 
group,  namely,  metaphosphoric  acid.  This  acid,  however,  is  the  link 
adjacent  to  the  mineral  acids,  in  which  proximity  the  hydrogen  has 
become  wholly  typic,  and  hence  the  definition  is  not  appropriately 
applicable  in  this  case. 
Assuming  that  the  acids  of  phosphorus  are  formed  from  trihydric 
phosphide  (PH3)  by  the  interpolation  of  oxygen,  and  we  have  : 
Hypophosphorous  acid,  P02H3=P02H2,H=POH2(OH). 
Phosphorous  acid,  P03H3=P03H,H2==POH(OH)2. 
Orthophosphoric  acid,  P04H3=P04,H3==PO(OH)3. 
But  comprehending  all  the  acids,  and  we  have,  more  fully,  thus  : 
Hypophosphorous  acid,  P204H6=P204H4,H2=(PO)2H4(OH)2. 
Phosphorous  acid,  P206H6=P206H2,H4^PO)2H2(OH)4. 
Orthophosphoric  acid,  P208H6^P208,H6=(P204)H2(OH)4. 
Pyrophosphoric  acid,  P207H4=P207,H4=(P204)H(OH)3. 
Metaphosphoric  acid,  P206H2=P206,H2=(P204)(OH)2. 
This  arrangement  reveals  a  number  of  very  important  facts.  It 
shows  the  regular  gradation  and  development  of  the  series  in  a  most 
lucid  and  comprehensive  manner,  and  the  gradual  evolution  from  the 
hydrophosphorus,  PH3,  becomes  evident  in  every  member.  The  rela- 
tion to  the  carbon  acids  is  most  apparent  in  the  two  lowest  derivatives, 
in  which  the  accumulation  of  oxygen  has  not  entirely  overcome  the 
direct  contact  of  phosphorus  and  hydrogen.  In  the  hypophosphorous 
acid,  only  one-third  of  the  combined  hydrogen  is  typic,  and  in  the 
phosphorous  acid  two-thirds.  The  evolution  of  phosphorus  hydrides 
from  either  of  these  two  acids  by  means  of  heat  shows  that  the  whole 
