158  UREA  AS  A  DIRECT  SOURCE  OF  NITROGEN  TO  PLANTS. 
In  addition  to  the  above-named  substances  (which,  it  will  be 
observed,  contains  no  nitrogen,)  a  solution  of  urea  was  applied 
thrice  in  each  week  to  basins  Nos.  1  and  2,  and  a  solution  of  sul- 
phate of  ammonia  to  No.  3.  No.  4  was  intended  as  a  check 
upon  the  experiments  with  the  urea,  and  to  it,  therefore,  no  ni- 
trogenous substance  was  applied.  All  the  basins  were  covered 
with  glass  shades,  the  air  supplied  to  the  interior  of  each  being 
freed  from  ammonia  by  treatment  with  dilute  sulphuric  acid. 
The  urea  used  in  my  experiments  was  prepared  by  the  follow- 
ing process : — 
28  parts  of  dried  ferrocyanide  of  potassium  and  14  parts  of 
peroxide  of  manganese,  thoroughly  mixed,  were  heated  to  dull 
redness.  The  resultant  mass,  after  cooling,  was  treated  with 
cold  water,  and  the  solution  thus  obtained,  mixed  with  20-5  parts 
of  crystallized  sulphate  of  ammonia,  sulphate  of  potash  and 
cyanate  of  ammonia  were  formed  ;  and  the  latter,  on  the  appli- 
cation of  a  gentle  heat,  was  converted  into  urea.  I  did  not  sep- 
arate the  sulphate  of  potash,  as  its  presence  did  not  interfere 
with  the  results  of  the  experiments. 
The  felspar  in  basins  Nos.  1  and  2  was  occasionally  washed 
with  distilled  water,  and  the  washings  tested  for  ammonia.  I 
did  not,  however,  in  a  single  instance,  detect  the  presence  of 
this  substance,  which  proves  that  the  urea  was  not  converted  in- 
to carbonate  of  ammonia. 
The  barley  experimented  on  was  the  variety  known  as  cheva- 
lier barley.  The  growing  plants  were  abundantly  supplied  with 
carbonic  acid  gas  and  distilled  water.  The  plants  were  thinned 
at  an  early  stage  of  their  growth,  so  that  there  remained  but  15 
plants  to  each  square  foot  of  surface. 
The  results  of  the  experiments  were  as  follow  : — 
No.  1. — Period  of  complete  germination,  within  5  days. 
Period  of  ripening,  within  107  days. 
Mean  height  of  plants,  including  the  ears,  29  inches. 
Average  return  from  the  seed,  9  stalks. 
Average  produce  in  seed,  28  grains  to  each  stalk. 
Size  of  grain,  14,786  to  the  pound. 
Amount  of  nitrogen  in  100  parts  of  the  dried  grain,  2-740. 
No.  2. — Period  of  perfect  germination,  within  6  days. 
Period  of  ripening,  within  112  days. 
