PHOSPHORUS  AND  MATCH  MANUFACTURES* 
55 
pipe  into  the  mixture  to  facilitate  the  action  of  the  sulphuric 
acid  upon  the  powder. 
The  changes  which  bone-ash  or  other  varieties  of  phosphate 
of  lime  undergo  in  the  above  operation  are  these  :  the  oil  of 
vitriol  or  sulphuric  acid  gradually  unites  with  the  lime  and  forms 
sulphate  of  lime,  and  sets  the  phosphoric  acid  free  ;  so  that 
after  the  process  there  remains  a  semi-fluid  mixture  of  a  solid 
substance,  sulphate  of  lime  (gypsum  or  plaster  of  Paris),  with  a 
fluid  body,  phosphoric  acid,  separable  by  filtration. 
The  creamy  mixture  is  now  transferred,  by  means  of  ladles, 
to  a  filter  or  drainer,  from  which,  with  the  aid  of  occasional  stir- 
ring, the  phosphoric  acid  filters  into  a  vessel  beneath.  Water 
is  added  to  the  drained  contents  of  the  filter  until  the  drainings 
cease  to  taste  acid.  The  sulphate  of  lime  or  gypsum  is  then  re- 
moved, in  its  damp  state,  to  a  furnace  or  other  source  of  heat 
and  dried,  and  constitutes  a  residuary  product  suitable  for  the 
manufacture  of  artificial  manures. 
The  dilute  filtered  solution  of  phosphoric  acid,  containing 
some  phosphate  of  lime  and  a  small  quantity  of  sulphate  of  lime 
dissolved  in  it,  is  transferred  to  leaden  vessels  and  slowly  evap- 
orated over  a  gentle  fire  ;  the  small  quantity  of  gypsum  then 
deposits  itself  upon  the  bottoms  of  these  vessels  and  is  removed 
by  scraping.  The  liquid  is  deprived  of  as  much  more  of  its 
water  as  possible  by  further  evaporation  in  similar  vessels,  and 
cooling  acquires  the  consistence  of  cocoa-nut  butter. 
The  butter-like  paste  is  then  well  mixed  with  a  due  propor- 
tion of  powdered  charcoal,  and  the  mixture  heated  in  furnaces 
of  brick  or  iron  until  it  is  brought  into  as  dry  a  powder  as  can 
be  attained.  The  powder  consists  of  charcoal,  phosphoric  acid 
(a  compound  of  phosphorus  and  oxygen),  a  little  phosphate  of 
lime,  and  a  little  water,  which  is  chemically  combined  with  the 
phosphoric  acid,  and  not  capable  of  removal  by  the  means  yet 
applied. 
We  have  already  alluded  to  the  intense  heat  employed  by 
Boyle  and  Hanckwitz  in  their  distillation  of  phosphorus ;  the 
same  is  also  necessary  in  the  present  mode  of  manufacture. 
The  vessels  in  which  the  phosphorus  is  separated  consist  of  a 
number  (about  ten)  of  small  retorts,  of  a  convenient  shape,  care- 
fully constructed  of  the  most  refractory  fire-clay,  narrowed  at 
