392      SOLUTION  OE  PYROPHOSPHATE  OF  SODA  AND  IRON. 
sulphatis,  the  former  of  which  represents  480  grains  crystallized 
protosulphate  of  iron  in  each  fluidounce,  consequently  1  gramme 
in  each  cubic  centimeter,  while  the  latter  contains  only  half  that 
quantity  in  the  same  measure, — namely,  240  grains  in  the  fluid- 
ounce,  or  "5  grm.  in  each  cubic  centimeter.  Instead  of  the  pro- 
* '  tosulphate  of  iron  ordered  by  Persoz,  corresponding  quantities 
of  these  solutions  were  used. 
1.  The  pyrophosphate  of  iron  was  made  from  tersulphate  of 
iron  at  the  boiling  point  of  water ;  the  precipitate  was  insoluble 
in  the  soda  salt ;  the  liquid  reacted  acid. 
2.  Made  at  125°  F.  solution  was  effected,  but  precipitation 
commenced  before  the  whole  of  the  liquid  could  be  filtered. 
3.  Temperature  100°  F.  Solution  complete ;  the  filtrate  re- 
mained clear  for  several  days.  At  the  end  of  ten  or  twelve  days 
a  bulky  precipitate  had  appeared ;  the  clear  supernatant  liquid 
was  separated,  but  continued  to  precipitate.  Exclusion  of  light 
did  not  prevent  precipitation. 
4.  Ordinary  temperature  (between  70  and  80°  F.)  Solution 
took  place  slowly,  the  liquid  retained  a  slight  opacity ;  precipi- 
tation commenced  in  a  few  days. 
5.  The  ferric  pyrophosphate  was  made  from  subsulphate  of 
iron  at  the  boiling  point ;  solution  took  place  rapidly ;  color 
brown-yellow.    Precipitation  takes  place  slowly. 
6.  Operated  at  ordinary  temperature.  Solution  takes  place 
without  difficulty ;  liquid  colorless,  perfectly  transparent ;  be- 
coming brownish-yellow  on  boiling  ;  slight  precipitation  as  under 
No.  5. 
7.  Ammonia  added  to  Nos.  4  and  6  produced  a  reddish-brown 
color  ;  liquid  clear  and  transparent  after  seven  weeks.  . 
8.  Sulphuric,  muriatic,  nitric  or  phosphoric  acid  added  to  No. 
6  until  the  reaction  was  acid,  instantly  caused  a  turbidity  and 
induced  precipitation,  which  gradually  increased. 
9.  Syrup  added  to  No.  7  remained  transparent  in  thin  layers 
after  seven  weeks,  but  the  color  was  darkened,  so  as  to  appear 
brown-black  in  reflected  light. 
10.  Little  alcohol  added  to  No.  9  remained  transparent  for 
several  days,  then  it  became  darker  in  color  and  gradually  pro- 
