430 
"USE  OF  MUKEXIDE  IN  DYEING. 
All  attempts  to  fix  the  murexide  purple  upon  cotton  or  silk 
have  failed  ;  on  wool,  however,  it  is  permanent. 
Light  appears  to  have  little  action  upon  murexide  purple, 
which  has  the  advantage  over  the  colors  produced  from  cochineal 
in  being  generally  more  solid  and  durable. 
With  regard  to  the  sources  whence  alloxan — or  uric  acid,  the 
substance  from  which  it  is  derived — may  be  obtained,  it  may  be 
observed  that  guano  is  rich  in  uric  acid,  and  likewise  the  excre- 
ments of  pigeons,  carnivorous  birds,  and  silkworms. 
M.  Schlumberger  has  indulged  in  some  curious  speculations 
relative  to  the  existence  of  this  coloring  matter  ready  formed  in 
nature,  which  it  may  be  interesting  to  notice.    M.  Sacc  has 
found  that  poultry,  and  especially  birds  with  very  brilliant 
plumage,  such  as  the  different  paroquets,  do  not  produce  sensible 
traces  of  uric  acid  during  their  period  of  moulting,  whilst  the 
quantity  is  very  large  when  their  feathers  are  fully  developed. 
The  question  naturally  suggests  itself,  what  becomes  of  the  uric 
acid  in  the  former  case  ?   May  it  not  be  transformed  by  some  as 
yet  unknown  metamorphoses  in  the  animal  body  into  a  substance 
like  alloxan,  capable  of  coloring  the  feathers  ?    Murexide,  as 
we  have  observed,  is  green  by  reflected  light :  a  substance,  then 
which  gives  violet  (red  and  blue)  and  green  (yellow  and  blue) 
can  undoubtedly  produce  all  shades  of  colors  which  are  made  up 
of  those  three  colors.    How  curious  if  it  should  hereafter  be 
found  that  murexide  was  indeed  the  source  of  all  the  varied  hues 
of  birds'  plumage  !    Still  further,  it  is  chiefly  those  animals 
which  have  but  one  means  of  exit  for  their  excrements,  and  who 
produce  large  quantities  of  uric  acid,  that  exhibit  a  display  of 
coloring.    Thus,  for  example,  we  have  the  skin  of  the  serpent 
and  lizard,  the  scales  of  fish,  the  wings  of  butterflies,  often 
colored  in  the  most  gorgeous  manner,  whilst  the  skins  of  the 
mammalia  are  dull,  and  without  that  iridescence  and  metallic 
lustre  which  is  so  characteristic  of  the  coloring  of  some  of  the 
classes  of  animals  mentioned.    These  are,  however,  mere  specu- 
lations, but  they  nevertheless  lead  to  a  very  unexpected  supposi- 
tion.   The  ancients  were  acquainted  with  a  process  for  dyeing 
wool  of  a  fine  purple,  which  has  been  lost  to  our  days,  or  at  least 
is  only  practised  in  the  East.    Tradition,  however,  tells  us  that 
this  beautiful  purple  tint  was  produced  by  pounding  a  quantity 
