I 
ON  CHEMISTRY  APPLIED  TO  THE  ARTS.  261 
The  valuable  and  extensive  researches  of  Messrs.  Lawes  and 
Gilbert  and  Messrs.  Boussingalt  and  Ville  have  not  only  demon- 
strated the  importance  of  phosphates  to  the  growth  of  cereal  and 
root  crops,  but  also  that  phosphates  determine,  in  a  great  mea- 
sure, during  vegetation,  the  absorption  of  nitrogen  from  the 
nitrates  or  from  ammonia,  as  will  be  seen  by  the  following 
table : — 
Amount  of  Nitrogen  fixed  hy  Wheat  under  the  influence  of  fol- 
lowing Salts  : — 
Without  With 
nitrogenated  nitrogenated 
compounds.  compounds. 
Phosphate  of  lime  and 
alkaline  silicate       .       .      8*15  20*08 
Phosphate  of  lime       .       .      7-25  1947 
Earths  and  the  alkaline  silicates  5-71  1T"16 
Earth                                    3-00  9-50 
Bone-black  or  Char. — In  1800  Lowitz  made  the  interesting 
observation  that  wood  charcoal  possessed  the  remarkable  pro- 
perty of  removing  coloring  matters  from  their  solutions.  In 
1811  Figuier  also  observed  that  animal  black  had  far  greater 
decolorating  power  than  wood  charcoal,  and  bone-black  has  con- 
sequently become  one  of  the  principal  agents  in  sugar-refining, 
and  has  been  the  means,  more  than  any  other  substance,  of  pro- 
ducing good  and  cheap  white  sugars.  To  give  you  an  idea  of 
the  extent  to  which  bone-black  is  used  at  the  present  day  for 
decolorating  purposes  in  the  refining  of  sugar,  I  may  state  that 
in  Paris  alone  it  is  estimated  that  about  11,000,000  kilogrammes 
of  bones  are  used  annually  for  that  purpose.  The  preparation 
of  bone-black  is  simple  in  principle.  It  consists  in  placing  in 
cast-iron  pots  about  50  lbs.  of  broken  boiled  bones,  that  is,  bones 
which  have  been  deprived  of  their  fat — of  most  of  their  osseine — 
and  piling  these  pots  in  a  furnace,  .where  they  are  submitted  to 
a  gradually  rising  temperature  during  twenty-four  hours,  such 
as  will  completely  decompose  the  organic  matter,  but  not  so  high 
as  to  partly  fuse  the  bones  and  thus  render  them  unfit  for  their 
applications.  But  a  more  economical  process  is  generally 
adopted.  It  consists  in  introducing  the  crushed  bones  into 
horizontal  retorts,  which  arc  themselves  in  connexion  with  con- 
