ON  THE  SUPERPHOSPHATE  OF  DECOMPOSED  EONES.  81 
The  soluble  salts  of  iron  have  an  injurious  action  upon  decom- 
posed bones  as  a  manure.  A  loss  must  take  place.  A  solution 
of  sulphate  of  iron  immediately  produces  a  white  precipitate  with 
an  aqueous  solution  of  superphosphate,  and  this  perceptibly  in- 
creases, so  that  the  greater  part  of  the  phosphoric  acid  is  soon 
separated  as  an  insoluble  iron-salt. 
Bones  decomposed  with  sulphuric  acid  are  extracted  with  water 
at  a  gentle  heat.  The  yellowish  filtrate  has  a  strongly  acid  re- 
action. 
15  cub.  centims.  of  solution  contained  0*0103,  or  0-0686  per 
cent,  of  sulphuric  acid,  and  0-0225  or  0-15  per  cent,  of  lime, 
leaving  0-0153  of  lime  for  the  phosphoric  acid. 
15  cub.  centims.  of  the  solution  contained  0-1047,  or  0-698 
per  cent,  of  phosphoric  acid.  The  equivalent  proportion  of  the 
lime  to  the  phosphoric  acid  is  therefore  as  1  to  3. 
15  cub.  centims.  of  the  solution  were  mixed  with  carbonate  of 
ammonia  until  the  production  of  a  weak  alkaline  reaction.  A 
strong  white  precipitate  was  produced,  which  gave  on  analysis 
0-043,  or  0-286  per  cent,  of  lime,  and  0-0313,  or  0-2086  per 
cent,  of  phosphoric  acid.  Proportion  of  lime  to  phosphoric  acid 
as  1  to  3. 
The  filtrate  still  contained  0-0706,  or  0-4706  per  cent,  of  phos- 
phoric acid.    The  whole  quantity  of  phosphoric  acid  was  0-1047 
Obtained  0-1019 
Loss  0-0028 
Experiment  with  Marl. — The  superphosphate  remained  for 
several  days  in  contact  with  the  marl.  It  was  then  filtered,  and 
the  fluid  brought  to  its  original  quantity  (15  cub.  centims.).  The 
filtrate  had  an  acid  reaction.  It  contained  0.101,  or  0-073  per  cent, 
of  lime,  and  0-0783,  or  0-5835  per  cent,  of  phosphoric  acid. 
From  these  experiments  it  appears  that  it  is  not  advisable  to 
convert  the  superphosphate  again  into  tribasic  phosphate  of  lime 
by  the  addition  of  lime.  By  the  action  of  ammonia  upon  the 
acid  product,  the  desired  state  of  fine  division  is  at  once  pro- 
duced, whilst  another  portion  of  the  phosphoric  acid  can  be 
drawn  up  by  the  plants  in  the  form  of  phosphate  of  ammonia  at 
the  commencement  of  vegetation.  This  is  also  the  case  when 
carbonate  of  lime  acts  upon  the  superphosphate. — Chemical 
Grazette,  September,  1856,  from  Liebig' s  Annalen,  July,  1856. 
6 
