THE  PREPARATION  OF  LITMUS. 
227 
one  of  his  grand -children  could  not  be  suckled  by  its  mother,  and 
that  another  required,  besides  his  mother's  milk,  a  more  concen- 
trated food.  In  both  cases,  as  well  as  in  other  families  where  it 
had  been  introduced,  the  soup  proved  an  excellent  food,  the 
children  thrived  perfectly  well,  and  many  a  petty  suffering  dis- 
appeared after  some  weeks'  use  of  the  soup.  He  often  takes  it 
prepared  with  ten  parts  of  milk  and  two  parts  of  malt  flour,  with 
tea,  for  his  breakfast.  He  adds  that  "  Dr.  Von  Pfeufer,  the  most 
renowned  physician  in  Munich,  has  induced  the  apothecaries  of 
the  town  to  keep  for  sale  a  mixture  of  half  an  ounce  of  malt  flour 
and  seven  grains  and  a  quarter  of  bicarbonate  of  potash,  milk 
and  wheat  flour  being  supposed  to  be  in  every  house.  The  malt 
flour  ought  to  be  always  freshly  made  from  the  malt. — Boston 
Medical  and  SurgicalJournal,  March  16, 1865,  from  The  Lancet, 
Jan.  7. 
THE  PREPARATION  OF  LITMUS. 
By  M.  De  Luynes. 
Two  different  products  are  included  under  the  name  of  litmus, 
that  in  sheets  and  that  in  cakes.  The  latter  is  used  as  a  reagent ; 
with  water  or  alcohol  it  gives  a  violet  blue  liquid,  which  becomes 
light  red  by  contact  with  acids. 
The  process  for  preparing  litmus  consists  in  coloring  orchil 
lichens  under  the  influence  of  air  and  ammonia,  in  the  presence 
of  a  large  excess  of  alkaline  carbonate.  M.  Gelis  has  tested  the 
exactness  of  these  indications,  and  has  obtained  very  excellent 
litmus  by  treating  orchil  lichens,  mixed  with  half  their  weight  of 
carbonate  of  potash,  by  ammonia.  But  whatever  the  mode  of 
preparation,  either  carbonate  or  sulphate  of  lime  is  added  to  the 
litmus  paste,  to  dry  and  preserve  the  coloring  matter,  which  con- 
stitutes but  a  very  small  fraction  of  the  total  weight  of  the  cakes. 
M.  Dumas  has  shown  that  when  orcine  becomes  colored  under 
the  influence  of  air  and  ammonia,  it  produces  only  one  coloring 
matter,  which  is  orceine.  By  modifying  the  circumstances  under 
which  orcine  becomes  colored,  M.  de  Luynes  has  succeeded  in 
preparing  a  product  identical  in  its  properties  with  litmus.  As 
litmus  has  not  yet  been  obtained  by  means  of  orcine,  and  as 
some  chemists  seem  to  doubt  whether  it  can  be  so  derived,  M. 
