ACTION  OF  BICHROMATE  OF  POTASSA  IN  DYEING. 
131 
It  is  difficultly  soluble  in  cold  water ;  boiling  water  dissolves 
it  in  a  large  quantity,  and  deposits  it  on  cooling.  It  is  very 
soluble  in  alcohol,  ether  and  the  fixed  and  volatile  oils;  concen- 
trated sulphuric  acid  dissolves  it  and  is  colored  yellow. 
It  dissolves  without  alteration  in  diluted  acids.  Liquor  potassse 
also  readily  dissolves  it  and  yields  it  unaltered  on  adding  an 
acid.  It  does  not  decompose  the  alkaline  carbonates  cold  or 
hot. 
Submitted  to  analysis,  it  affords  a  per  centage  of  carbon 
75*22;  hydrogen  3*98;  oxygen  20*20,  which  lead  to  the  formula 
C20  H6  O4. 
The  properties  of  this  substance  are  analogous  to  those  of 
coumarin  of  Tonka  bean,  which  the  author,  some  years  since, 
found  in  the  leaves  of  Anagroecum  Fragrans,  of  the  Isle  of 
Mauritius ;  but  their  identity  is  not  complete,  differing  in  odor, 
point  of  fusion  and  composition.  As  it  appears  to  be  a  distinct 
proximate  principle,  the  author  suggests  for  it  the  name  vanillin. 
It  is  well  know  that  vanilla,  enclosed  in  cases,  is  often  found 
covered  with  crystals,  known  in  France  under  the  name  "  givre" 
or  frost.  Bucholz  and  Vogel  considered  these  crystals  to  be 
benzoic  acid.  The  author  considers  them  identical  with  vanillin 
as  it  presents  the  same  crystalline  form,  fusing  point  and  solu- 
bility in  water,  alcohol  and  ether.  The  givre  dissolved  in  alco- 
hol has  a  slight  action  on  litmus  paper,  but  Soubeiran,  who 
noticed  this,  did  not  hesitate  to  deny  its  acid  character. 
The  pre-existence  of  vanillin  demonstrates  that  the  crystal- 
line substance,  which  appears  on  its  surface,  is  not  the  product 
of  oxidation  of  an  essential  oil,  as  has  been  supposed,  but  is 
vanillin,  which  is  thus  transferred  to  the  surface,  under  favora- 
ble circumstances  for  the  evaporation  of  the  juices  of  the  bean. 
— Journ.  de  Pharm.  et  de  Ohimie,  Janv.,  1859. 
ON  THE  ACTION  OF  BICHROMATE  OF  POTASSA  IN  DYEING. 
By  John  S.  Blockey  and  Herbert  Sugden. 
It  is  well  known,  that  bichromate  of  potassa  is  largely  used 
in  dyeing  certain  colors  with  logwood,  the  cloth  or  yarn  being 
boiled  in  a  solution  of  this  salt  for  a  period  varying  from 
