DISINFECTION  OF  NITROGENOUS  MANURE. 
147 
This  process  is  employed  after  the  ammonia  salts  have  been  fixefl. 
An  abundance  of  silicate  of  soda  is  mixed  with  the  night-soil,  and 
then  sulphuric  or  some  other  strong  acid  is  added  to  precipitate  the 
silica:  Na  0,  Si  Oa+S  03=Na  0,  S  03+Si  02.  The  silicate 
of  soda  is  very  cheaply  prepared  by  heating  in  a  furnace  a  mix- 
ture of  common  salt  and  sand:  Na  Cl+Si  02=Na  0,  Si  02-f 
Cl.  As  the  refuse  zinc  salt  may  be  employed  for  artificial 
manure,  Gaultier  de  Claubry  has  suggested  that  the  extensive 
utilization  of  such  refuse  in  this  way  may  so  reduce  the  expense 
of  operating  the  galvanic  battery,  as  to  introduce  it  as  common 
power  aparatus. 
In  Paris,  it  was  found  that  one  man  with  a  horse  would  manu- 
facture, in  the  old  way,  with  plaster  and  coal,  25  tons  of  poud- 
rette  per  day,  and  that  the  entire  cost  of  manufacture  amounted 
to  only  $1.87  per  ton.  According  to  chemical  analysis  the 
nitrogen  in  night-soil  is  13  per  cent,  of  the  dry  matter.  Now, 
the  best  Peruvian  guano  contains  only  14  per  cent,  of  nitrogen, 
whilst  the  average  quality  contains  but  6  or  7  per  cent.  There- 
fore poudrette,  properly  prepared,  will  be  as  valuable  as  the  best 
Peruvian  guano,  and  of  twice  the  value  of  the  average.  The 
experience  of  farmers  sustains  the  results  of  analysis. 
The  nitrogen  in  urine  is  from  25  to  33  per  cent,  of  the  solid 
matter.  A  manure  prepared  from  urine,  and  sold  under  the 
name  of  urate,  is  a  most  powerful  fertilizer,  equal  to  four  times 
its  weight  of  average  guano,  or  twice  the  value  of  best  Peruvian, 
In  the  various  processes  of  manufacturing  poudrette,  it  is  too 
often  forgotten  that  the  night-soil  should  be  treated  before  the 
urine  is  decomposed.  The  urine  is  much  richer  than  the  faeces 
in  nitrogen.  The  nitrogen  in  urine  is  found  chiefly  in  that  re- 
markable compound  denominated  urea,  which  forms  white  pris- 
matic crystals,  quite  inodorous.  Urea  contains  two  atoms  of 
nitrogen,  two  of  carbon,  four  of  hydrogen,  and  two  of  oxygen, 
and  its  formula,  deduced  from  its  ultimate  analysis,  would  give, 
N2  C2  H4  02.  But  organic  chemistry  regards  such  a  formula  as 
empirical,  and  groups  these  elements  according  to  their  products 
of  decomposition,  and  the  compound  which  may  be  formed  by  a 
part  or  all  of  them  with  oxygen  or  with  the  halogens,  by  substi- 
tution or  otherwise. 
The  true  constitution  of  urea  is  expressed  by  the  following 
