340  PRESERVING  THE  COLORING  MATTER  OF  LITMUS. 
yeast.  Hence  it  is  clearly  impossible  at  present  to  express  the 
so  called  fermentation  changes  by  an  equation.  The  author 
considers  them  as  a  series  of  transformations  which  take  place 
simultaneously  or  consecutively,  and  which  may  some  day  be 
individually  explained  by  an  equation  comparable  to  that  which 
expresses  the  change  in  starch  under  the  influence  of  diastase. 
— Chemical  News,  London,  April  16th,  1864. 
A  METHOD  FOR  PRESERVING  THE  COLORING  MATTER  OF 
LtTMUS. 
By  Dr.  Yogel. 
It  is  well  known  that  litmus  tincture  so  frequently  used  in 
analytical  researches,  alters  progressively,  even  in  a  closed  ves- 
sel, and  losing  its  blue  color  becomes  yellowish  brown.  That 
this  change  of  tint  is  the  result,  not  of  the  destruction  of  the 
coloring  matter,  but  of  simple  deoxidation,  is  shown  by  shaking 
the  tincture  in  contact  with  the  air,  when  the  blue  color  will 
reappear.  Litmus  dye,  as  M.  Mohr  has  remarked,  may  be 
conveniently  preserved  in  open,  partly-empty  flasks,  the  mouths 
being  lightly  plugged  with  cotton,  simply  to  exclude  dust.  The 
author  has  found,  nevertheless,  that  litmus  dye,  especially  in  a 
slightly  concentrated  solution,  becomes,  after  a  time,  turbid  and 
reddish.  The  latter  phenomenon  is  probably  due  to  the  carbonic 
acid  of  the  air,  for  on  being  boiled  the  liquid  resumes  its  blue 
color.  M.  Vogel  now  uses  litmus  die  immediately  before  each 
experiment,  with  some  litmus  which  he  has  found  a  means  of 
preserving  unaltered,  and  which  he  dissolves  in  water. 
Th^  preparation  of  this  litmus  is  very  simple.  Take  16 
grammes  of  commercial  litmus,  reduce  it  to  a  fine  powder  and 
put  it  into  a  cylindrical  glass  phial,  with  120  cube  centimetres 
of  cold  distilled  water,  and  leave  for  twenty-four  hours,  taking 
care  to  stir  occasionally.  As  the  first  portion  of  the  liquid  ex- 
tract will  contain  all  the  free  alkali  of  the  litmus,  it  should  be 
set  aside,  and  on  the  residue  should  be  poured  a  fresh  quantity 
of  120  centimetres  of  distilled  water ;  it  should  then  again  be 
left  for  twenty-four  hours,  and  shaken  at  intervals.  Then  de- 
cant a  second  time  and  divide  the  liquid  into  two  equal  parts, 
