"^"AiS'isss™"}  F^'^"'^^<^  Citro- Phosphate  and  Citro-Pyrophosphate.  165 
phide  of  iron  is  placed  in  the  flask  with  some  diluted  sulphuric  acid ; 
this  will  supply  the  hydrogen  sulphide.  The  bromine  and  water  having 
been  placed  in  the  percolator,  the  gas  is  permitted  to  pass  through  it 
tintil  all  the  bromine  has  been  converted  into  hydrobromic  acid,  which 
will  be  indicated  by  its  loss  of  color  and  of  the  peculiar  odor  of  bromine  ; 
the  solution  is  then  filtered  from  the  sulphur  and  concentrated  to  the 
specific  gravity  cf  1*077,  which  corresponds  with  a  ten  per  cent,  solu- 
tion, this  being  the  strength  indicated  by  the  Pharmacopoeia  of  1880. 
PERRIC  CITRO-PHOSPHATE  AND  CITRO-PYROPHOS- 
PHATE AND  THEIR  DOUBLE  SALTS. 
By  R.  Rother. 
All  acids,  properly  so  called,  are  generated  by  the  union  of  acid 
oxides  and  water,  and  bases  are  formed  from  basic  oxides  in  a  similar 
manner.  This  mode  of  action  is  distinctly  chemical  in  what  may  be 
termed  the  upper  end  of  the  series,  but  towards  the  opposite  extreme 
the  chemical  character  becomes  less  and  less  distinct  until  in  the  vanish- 
ing terms  its  nature  is  wholly  lost.  In  these  latter  cases  the  acid  or 
basic  oxide  either  remains  insoluble  or  simply  dissolves  in  the  water, 
unattended  by  chemical  effect.  In  those  instances  where  chemism  is 
€xerted,  the  resulting  compound  is  called  either  a  hydrate,  a  hydroxide, 
or  a  hydride,  according  to  the  way  in  which  its  formula  is  written. 
For  example,  sulphuric  acid  can  be  indicated  as  SO3.OH2,  as  S02(OH)2, 
or  as  SO4H2,  or  even  as  S03H(0H).  The  first  form  would  be  termed 
sulphuric  hydrate ;  the  second,  sulphuryl  hydroxide ;  the  third,  sul- 
phione  hydride  or  hydric  sulphate ;  and  the  fourth,  sulphonic  hydrox- 
ide. Caustic  potash  can  be  represented  by  K2O.OH2,  K(OH),  or 
{KO)H.  The  first  would  be  potassic  hydrate  ;  the  second,  potassium 
hydroxide ;  and  the  third,  potassoxyl  hydride.  There  are  numerous 
instances  when  a  particular  one  of  these  forms  would  designate  the 
combination  more  appropriately  than  another,  but  for  general  conven- 
ience and  the  sake  of  consistent  uniformity  in  accord  with  the  new 
nomenclature,  these  compounds  are  all  styled  hydrates.  Now  it  is 
everywhere  either  distinctly  enunciated  or  implied  that  a  hydrate  is 
generated  by  compounding  water  with  an  oxygenated  radicle,  and  that 
the  oxygenated  radicle  is  reconstituted  by  its  deprivation  of  the  water. 
'The  fact,  therefore,  could  not  be  clearer  than  that  such  a  basic  or  acid 
