354 
London  Purple. 
f  Am.  Jour.  Pharm. 
\       July,  1880. 
LONDON  PURPLE. 
By  C.  V.  Riley. 
From  the  "American  Entomologist,"  Bulletin  No.  3  of  the  U.  S.  Entomological  Commission. 
This  powder  is  obtained  in  the  following  manner  in  the  manufacture 
of  anilin  dyes.  Crude  coal  oil  is  distilled  to  produce  benzol.  This 
is  mixed  with  nitric  acid  and  forms  nitro-benzol.  Iron  filings  are  then 
used  to  produce  nascent  hydrogen  with  the  excess  of  nitric  acid  in  the 
benzol.  When  distilled,  anilin  results  :  to  this  arsenic  acid,  to  give 
an  atom  of  oxygen  which  produces  rose  anilin,  and  quicklime  are  added 
to  absorb  the  arsenic.  The  residuum  which  is  obtained  by  filtration  or 
settling  is  what  has  been  denominated  "  London  Purple/'  the  sediment 
being  dried,  powdered  and  finely  bolted.  The  powder  is,  therefore, 
composed  of  lime  and  arsenious  acid,  with  about  25  per  cent,  of  car- 
bonaceous matter  which  surrounds  every  atom.  Experiments  which  I 
made  with  it  in  1878  impressed  me  favorably  with  this  powder  as  an 
insecticide,  and  its  use  on  the  Colorado  potato  beetle  by  Professors 
Budd  and  Bessey,  of  the  Iowa  Agricultural  College,  proved  highly 
satisfactory.  I  was,  therefore,  quite  anxious  to  test  .its  effect  on  the 
cotton  worm  in  the  field  on  a  large  scale,  and  in  the  winter  of  1878-79 
induced  the  manufacturers  to  send  a  large  quantity  for  this  purpose  to 
the  Department  of  Agriculture.  The  analysis'  made  of  it  by  Prof. 
Collier,  the  chemist  of  the  Department,  showed  it  to  contain  : 
Per  cent. 
Rose  anilin, 
12-46 
Arsenic  acid, 
43*65 
Lime, 
21-82 
Insoluble  residue. 
14-57 
Iron  oxide, 
i-i6' 
Water, 
2-27 
Loss, 
4*07 
100-00 
Through  the  liberality  of  the  manufacturers,  Messrs.  Hemingway  & 
Co.,  a  number  of  barrels  of  this  powder  were  placed  at  my  disposal 
the  past  season  and  distributed  to  various  observers  and  agents  in 
Georgia,  Alabama  and  Texas.  Early  in  the  spring  Mr.  A.  R.  Whitney, 
of  Franklin  Grove,  Illinois,  found  it  to  be  a  perfect  antidote  to  the 
canker  worms  which  had  not  been  prevented  from  ascending  his  apple 
trees,  and  the  experiments  of  those  whom  I  had  intrusted  to  make  them 
1  Ordinarily  the  rose  anilin  has  mixed  with  it  a  little  ulmic  acid  and  an  increase  of 
2  per  cent,  of  arsenic  acid. 
