198  Linseed  Cake  and  Meal.  {AmApm'Jmrm' 
grams  stirred  in  a  beaker  with  100  cc.  of  boiling  water.  Beakers 
of  one  size  are  employed,  so  that  the  more  or  less  swelling  of  the 
powdered  cake  and  the  smaller  or  greater  amount  of  liquid  which 
separates  can  be  compared.  It  is  also  noticed  whether  the  liquid  is 
quite  thin  or  whether  it  is  slimy.  With  regard  to  the  swelling  up, 
Camelina  swells  considerably  more  than  linseed.  Kobus  (Joe.  cit.) 
found  that  1  gram  of  linseed  kept  in  water  for  one  hour  weighed 
2-7-2-8  grams,  whilst  1  gram  of  Camelina  weighed  4-4  grams  after 
the  same  treatment.  A  part  of  the  liquid  is  tested  with  iodine  for 
starch  ;  only  a  light  blue  color  should  be  produced.  The  residue 
obtained  when  the  water  is  poured  off  is  examined  microscopically 
(Kobus,  loc.  cit.).  The  number  of  foreign  particles  is  estimated  in  5 
grams,  the  separation  being  effected  by  a  jet  of  water  on  the  sub- 
stance in  a  1-2  mm.  sieve.  Determinations  of  protei'ds,  fat,  and  ash 
are  also  made. 
The  injurious  substances  sometimes  found  in  linseed  cake  are 
corn-cockle,  containing  a  poisonous  substance,  saponin  or  githagin, 
the  seeds  of  Thlaspi  arvense,  which,  when  eaten  by  cows,  impart  a 
garlic-like  taste  in  the  milk,  the  hemp  seed,  which  causes  diarrhoea. 
Barium  sulphate  is  objectionable,  whilst  salt,  besides  being  good  for 
cattle,  has  the  advantage  of  making  the  cake  softer ;  on  the  other 
hand,  the  cake  becomes  quickly  moist  and  therefore  spoilt.  The 
poisonous  action  of  castor  oil  beans  was  first  shown  by  van  den 
Berghe.  Other  substances  doubtless  occur  which  are  more  or  less 
poisonous  or  injurious  when  much  of  them  is  present. 
The  results  of  experiments  made  at  Wageningen  show  that  in  5 
grams  of  substance  it  requires  only  16  seeds  of  Polygonum  lapathifo- 
liumy  13  of  P.  Convol.,  4  of  Galium  Aparine,  and  46  of  Camelina  to 
make  1  per  cent,  of  the  cake.  Each  seed  is  reckoned  as  follows  : 
Camelina  2,  Polygonum  lap.  6,  P.  Convol.  8,  Galium  Aparine  25  ;  if 
the  sum  of  the  numbers  found  exceeds  100,  the  cake  is  not  pure 
enough. 
In  most  cases  it  is  sufficient  to  magnify  70-80  times,  but  in  some 
cases  300  times.  For  the  detection  of  very  finely-powdered  sub- 
stances in  cake,  a  test  tube  is  half  filled  with  the  powdered  cake, 
treated  with  alcohol,  well  shaken,  and  allowed  to  settle ;  the  alcohol 
is  poured  off  and  some  of  the  fine  meal  which  floats  on  it  put  on  an 
object  glass.  The  alcohol  is  evaporated,  a  drop  of  glycerol  and 
aqueous  soda  added  and  pressed  with  a  second  glass.  When 
