196 
Linseed  Cake  and  Meal. 
( Am.  Jour.  Pharm . 
I       April.  1893. 
very  good  quality  for  the  production  of  oil.  The  American  seed  is 
of  about  the  same  quality;  the  Indian  (Bombay)  is  better,  whilst 
the  best  seed  is  that  from  Russia,  especially  South  Russia.  Most  of 
the  impurities  are  removed  by  sifting  ;  when  there  remains  only  4 
per  cent,  of  foreign  matter  (or  even  8  per  cent,  if  the  foreign  matter 
consists  of  oily  seeds),  the  seed  is  practically  pure.  With  regard 
to  the  manufacture  of  linseed  oil,  the  original  method  consisted  in 
pounding  the  seeds.  Now  there  are  two  methods  by  which  the  oil 
is  pressed  out ;  in  the  one  heat  is  applied  to  the  vessel  containing 
the  seeds  (either  by  direct  firing  or  steam) ;  in  the  other,  the  seed  is 
directly  treated  with  superheated  steam.  Another  method  is  to 
extract  with  light  petroleum.  The  residue  (cake  or  meal)  varies  in 
composition  according  to  the  method  employed.  Thus,  whilst  the 
residue  from  pressed  seeds  contains  about  32-36*4  per  cent,  of 
protein  and  9-11  per  cent,  of  fat,  the  residue  from  extracted  seeds 
contains  more  protei'ds  (40  per  cent.)  and  less  fat  (3-4  per  cent.). 
The  amount  of  mucilage  also  varies ;  where  direct  steaming  is 
employed  the  amount  is  diminished,  and  cake  so  obtained  will  keep 
for  years  without  becoming  mouldy.  This  is  also  the  case  with  cake 
prepared  by  the  light  petroleum  method,  but  this  seems  to  be  due, 
not  to  the  abstraction  of  mucilage,  but  to  the  action  of  the  light 
petroleum. 
For  adulteration,  not  only  vegetable  substances  but  also  heavy 
spar,  gypsum,  chalk  and  salt  are  employed ;  saw-dust  has  been 
found.  Rape-cake  meal  may  be  detected  by  stirring  in  water  in  a  glass 
cylinder  and  allowing  to  settle  ;  if  any  dark  particles  are  visible, 
rape  is  probably  present.  A  few  drops  of  aqueous  alkali  will  give 
an  intense  yellow  color  if  rape  is  present.  Amygdalin  does  not 
seem  to  be  actually  injurious,  but  mustard,  corn-cockle,  and  Came- 
Una  are  said  to  be  injurious,  whilst  castor  oil  is  poisonous  and  may 
cause  death.  Vegetable  imparities  can  mostly  only  be  detected 
microscopically  and  the  amounts  only  approximately  estimated. 
But  the  amount  of  fat,  and  especially  of  protein,  give  a  good  idea  as 
to  purity  or  otherwise.  When  mineral  impurities  are  present  they 
may  be  detected  by  the  amount  of  ash,  which  generally  should  not 
exceed  5  per  cent.  Cake  containing  over  14  per  cent,  of  water  can- 
not be  considered  as  pure. 
With  regard  to  fat,  it  should  be  noted  what  results  are  obtained 
when  the  substance  is  (1)  not  previously  dried,  (2)  when  dried  for  two 
