484  MEETING  OF  THE  BRITISH  ASSOCIATION. 
is  again  heated  as  before.  It  now  contains  from  28  to  30  per 
cent,  of  oxalic  acid,  which  exists  combined  with  the  soda,  and 
probably  also  with  the  potassa.  The  mass  is  then  treated  with 
water  which  dissolves  out  everything,  except  the  oxalate  of  soda, 
which  is  a  comparatively  insoluble  salt ;  and  this  insolubility  is 
probably  the  cause  why,  on  the  addition  of  water,  the  oxalate 
of  potassa  and  the  soluble  soda  salt,  of  formic  and  acetic  acids, 
interchange  their  constituents,  so  that  the  relatively  insoluble 
oxalate  of  soda  is  produced.  The  oxalate  of  soda  is  decomposed 
by  carbonate  of  lime,  producing  oxalate  of  lime,  which  is  then, 
finally,  treated  with  sulphuric  acid.  Two  pounds  of  sawdust 
yield  a  pound  of  oxalic  acid. 
7.  Garancin^  a  product  resulting  from  the  action  of  sulphuric 
acid  on  madder,  and  which  has  been  substituted  to  a  great  extent 
for  madder  itself  in  dyeing,  is  produced  to  the  amount  of  1200 
tons  per  annum  in  South  Lancashire.  All  the  madder  colors 
are  obtainable  from  garancin,  except  the  pinky  for  which  the 
dyer  requires  the  root  itself. 
8.  The  anilin  coloring  salts  are  largely  prepared  for  use  in 
dyeing. 
9.  Considerable  quantities  of  murexide  (purpurate  of  am- 
monia,) are  now  prepared  from  guano,  and  used  in  dyeing.  It 
produces  splendid  purples,  of  which  specimens  were  shown  to 
the  members. 
In  the  evening  a  grand  soiree  was  given  at  the  Free  Trade 
Hall,  attended  by  a  numerous  throng  of  ladies  and  gentlemen, 
with  a  display  of  a  vast  number  of  things,  illustrative  of  all  the 
kingdoms  of  nature,  and  most  of  the  branches  of  art ;  from  a 
Whitworth's  gun,  which  was  breech-loading,  and  would  carry  a 
12  pound  ball  six  miles,  to  a  series  of  bird's  eggs,  which  ap- 
peared sufficiently  numerous  to  be  counted  by  thousands. 
Sept.  6th.  In  the  evening,  Prof.  Miller  gave  a  lecture,  by  in- 
vitation, to  the  members  of  the  Association,  forming  an  audience 
of  nearly  2000,  upon  a  subject  of  much  interest, — the  spectrum 
analysis  of  Messrs.  Bunsen  and  Kirchoff.  The  lecture  was 
clear,  well  delivered,  and  admirably  illustrated.  It  has  long 
been  known  that,  when  the  rays  forming  the  solar  spectrum 
pass  through  a  slit  instead  of  a  round  opening,  the  spectrum 
itself  is  traversed,  at  right  angles,  by  a  great  number  of  black 
