BAKER'S  BREAD  OF  PHILADELPHIA. 
443 
flour,  is,  without  doubt,  to  be  found  no  where  in  London  ;"  in 
all  the  samples  of  bread  examined  by  him,  with  but  one  exception, 
alum  was  detected,  and  in  that  exception,  like  the  others,  a 
certain  quantity  of  potato  flour  or  pulp  was  found. 
Liebig  in  his  Chemical  Letters*  states,  that  he  saw  in  an  alum 
factory  in  Scotland,  small  mountains  of  finely  ground  flour  of 
alum  for  the  use  of  the  London  bakers.    In  the  same  work  he 
gives  an  explanation  of  the  mode  in  which  alum  acts  upon  the 
bread,  and  why  it  is  used  by  the  bakers.    When  the  millers 
moisten  their  grain  in  order  to  facilitate  the  grinding  and  do 
not  subsequently  dry  the  flour,  or  when  the  flour  is  exposed  to 
the  moisture  of  the  atmosphere,  the  gluten  acts  upon  the  starch 
to  form  acetic  and  lactic  acids,  which  render  the  gluten  soluble 
in  water,  which  it  is  not  originally  ;  the  dough  from  such  flour 
does  not  rise  well,  and  the  resulting  bread  is  heavy  and  of  bad 
appearance.    Several  salts  act  chemically  upon  the  altered 
gluten  of  such  flour  and  render  it  insoluble  again,  so  that  the 
resulting  bread  becomes  white,  elastic,  light,  and  as  if  made 
from  the  best  of  flour,  and  capable  of  retaining  more  water, 
yielding,  consequently,  more  bread  from  a  given  quantity  of 
flour.    The  salts  which  produce  this  effect  and  which  arc  used 
more  or  less  as  adulterations,  are  alum,  subcarbonate  of  magnesia, 
sulphate  of  copper,  and  sulphate  of  zinc.    The  use  of  blue 
vitriol  by  bakers  in  the  north  of  France  and  in  Belgium,  has 
been  abundantly  proved,  as  may  be  seen  by  a  reference  to  lire's 
Dictionary.    Carbonate  of  magnesia,  if  it  be  not  in  too  great  an 
excess,  cannot  be  regarded  as  injurious.    Liebig  has  recently 
made  some  experiments  upon  the  use  of  lime  water  in  the  baking 
of  bread,  and  found  that  five  pounds  of  a  saturated  solution  of 
lime  water  for  every  19  lbs.  of  flour,  gave  a  bread  of  fine  ap- 
pearance, and  which  he  deems  more  wholesome  than  if  made  by 
any  other  process,  as  such  treatment  supplies  to  bread  the 
deficiency  of  lime  which  places  it  below  peas  and  lentils  in 
nutritive  power.f    He  proposes  therefore  to  substitute  the  harm- 
less lime  water,  which  acts  in  a  similar  manner,  for  the  injurious 
adulterations  in  frequent  use. 
*  P.  541  of  Third  German  Edition. 
f  Liebig  calculated  the  amount  of  lime  in  such  bread,  and  finds  it  equal 
to  what  is  naturally  present  in  the  seeds  of  the  Leguminosas, 
