270  ON  COLOR  OBTAINED  FROM  COAL  TAR  PRODUCTS. 
of  alloxane,  a  product  discovered  by  Liebig  and  Wohler,  in 
heating  urea  with  nitric  acid.  The  fabric  so  prepared  was  dried, 
and  when  submitted  to  heat,  a  fine  crimson  was  generated,  the 
intensity  of  which  was  increased  by  the  fumes  of  ammonia.  But 
owing  to  the  difficulty  of  obtaining  a  color  of  uniform  shade,  Mr. 
Saac's  process  required  improvements,  and  these  have  been 
effected  by  Mr.  Schlumberger. 
The  process  followed  by  Messrs.  Saac  and  Schlumberger 
could  not  be  applied  to  silk  or  cotton  fabrics.  The  method  of 
dyeing  silk  with  murexide  was  discovered  by  M.  de  Pouilly,  who 
adopted  the  following  processes,  viz.,  dipping  the  silk  in  a  con- 
centrated solution  of  bichloride  of  mercury  mixed  with  murexide, 
squeezing  the  silk  well  and  hanging  it  in  the  air,  when  a  magni- 
ficent crimson  insoluble  compound  is  fixed  on  the  silk.  This 
effect  is  produced  from  the  fact  that  when  solutions  of  bichloride 
of  mercury  and  murexide  are  mixed  together,  an  insoluble  com- 
pound is  only  formed  after  the  lapse  of  an  hour  or  two. 
The  process  for  dyeing  cotton  is  due  to  Messrs.  Lauth  and 
Schlumberger,  and  consists  in  producing  on  cotton  a  purpurate 
of  lead  by  mordanting  with  nitrate  of  lead,  passing  into  an  al- 
kali, and  then  dyeing  in  a  solution  of  murexide  ;  in  order  to  give 
full  brilliancy  to  the  color,  it  is  lastly  passed  through  a  weak 
solution  of  bichloride  of  mercury.  This  process  was  further  im- 
proved by  Messrs.  Dolfus,  Meig  &  Co.,  in  France,  and  Mr. 
Lightfoot,  in  Lancashire,  by  printing  murexide  with  an  excess 
of  nitrate  of  lead,  and  subjecting  the  cloth  so  printed  to  the 
action  of  ammoniacal  fumes,  or  passing  it  through  a  solution  of 
caustic  soda  mixed  with  sal  ammoniac.  In  order  to  render  this 
substance  more  generally  useful,  it  remained  to  find  a  method 
for  obtaining  fast  colors  with  it  on  mixed  fabrics,  such  as  mous- 
seline  de  laine,  and  this  has  also  been  effected  by  Mr.  Schlum- 
berger. The  cloth  is  first  prepared  by  uniting  binoxide  of  tin 
with  the  wool.  This  object  is  attained  by  using  a  salt  known 
to  calico  printers  as  pink  salt,  the  double  chloride  of  ammonium 
and  tin,  and  then  printing  on  the  prepared  fabric  the  following 
mixture  :— 
1  part  of  murexide. 
6  parts  of  nitride  of  lead. 
2  parts  of  nitrate  of  soda. 
