**JtZ%  iP874EM*}    NotG  on  a  Reaction  of  Gallic  Acid,  373 
was  capable  of  dissolving.  These  approximate  so  closely  to  practical 
results,  that  they  seem  to  prove  the  accuracy  of  the  determinations  of 
the  solubility  in  pure  glycerin.  In  order  to  see  that  the  whole  of  the 
lead  was  precipitated  from  these  mixtures  by  sulphuric  acid,  the  fil- 
trates from  them  were  neutralized  with  ammonia,  and  then  treated 
with  sulphuretted  hydrogen,  without  causing  more  than  the  slightest 
discoloration. — Jour.  Ohem.  Soc,  (London),  June,  1874. 
NOTE  ON  A  REACTION  OF  GALLIC  ACID. 
By  Henry  R.  Procter,  F.C.S. 
If  a  solution  of  sodic  or  potassic  arsenate,  of  faintly  alkaline  re- 
action, be  added  to  one  containing  gallic  acid,  and  the  mixture  ex- 
posed to  the  air,  it  will  rapidly  absorb  oxygen,  and  develop  an  intense 
green  color.  If  the  liquid  be  undisturbed,  the  change  will  commence 
at  the  surface,  and  a  beautiful  green  layer  will  be  formed,  floating  on 
the  colorless  liquid ;  while  if  air  be  altogether  excluded,  no  apparent 
change  takes  place.  O05  mgr.  of  gallic  acid  will  produce  a  decided 
•coloration  in  1  c.c.  of  water.  The  arsenical  solution  must  not  be  acid, 
but  excess  of  alkali  causes  irregular  oxidation  and  the  formation  of 
brown  products. 
Dilute  acids  change  the  green  to  a  clear  purplish-red,  and  cautious 
neutralization  with  alkalis  restores  the  green,  but  any  considerable 
•excess  of  the  latter  destroys  the  color.  In  its  reactions  with  acids 
and  alkalis  it  shows  a  certain  similarity  to  the  coloring  matter  of  red 
cabbage,  but  in  most  other  reactions  the  two  are  completely  dissimilar. 
There  is  also  a  considerable  difference  in  their  absorption-spectra,  the 
cabbage-green  transmitting  a  broad  band  of  red,  while  the  gallic- 
green  does  not. 
Concentrated  nitric  and  sulphuric,  and  boiling  hydrochloric  acids 
change  the  color  to  a  pale  yellow,  which  is  not  restored  by  Ammonia, 
but,  in  the  case  of  nitric  acid,  is  changed  to  a  deep  orange-brown. 
Oxidizing  agents  mostly  change  the  color  to  an  orange-brown. 
Even  iodine  in  potassic  iodide  does  this  immediately. 
The  color  is  also  destroyed  by  reducing  agents.  Sulphuretted 
hydrogen  passed  into  the  acid  solution  rapidly  decolorizes  it,  with  no 
immediate  precipitation  of  arsenic  sulphide,  and  but  slight  deposition 
<of  sulphur.     Ammonie  and  sodic  sulphides  instantly  change  the 
