Am.  Jour.  Pharm.  1 
Dec,  1882.  J 
Influence  of  Gum  Arabic  in  Reactions. 
603 
substanceSj  and  then  poured  into  the  sulphuretted  Luchon  water,  the 
chemical  action  is  suspended,  i.  e.,  no  sulphide  of  mercury  is  formed.. 
The  authors  believe  that  although  tlie  experiments  of  M.  Lambron 
may  be  correct  his  interpretation  is  not  admissible. 
At  first  it  might  be  supposed  that  the  viscosity  of  the  solution  was- 
the  cause  of  the  non-precipitation.  But  this  is  not  the  case,  for  if  the 
syrup  of  gum  be  replaced  by  simple  syrup  or  glycerin  a  precipitate  is 
formed.  It  w^ould  therefore  appear  that  the  prevention  of  the  forma- 
tion of  the  precipitate  is  due  to  the  gum  or  vegetable  extract  contained 
in  the  precipitate,  and  this  was  confirmed  by  the  authors'  experiments. 
The  reaction  is  not  peculiar  to  Luchon  water  and  solutions  of  sulphu- 
retted hydrogen,  or  monosulphide  of  sodium  may  be  substituted  with- 
out sensibly  modifying  the  results. 
The  authors  therefore  thought  it  would  be  interesting  to  ascertain 
whether  gum  equally  prevented  the  precipitation  of  the  different  metal- 
lic sulphides,  using  solutions  suitably  diluted.  For  this  purpose  a 
titrated  solution  of  monosulphide  of  sodium  was  prepared  containing 
1'7  gram  of  sulphydric  acid  per  liter;  on  the  other  hand,  a  certain 
number  of  solutions  each  also  containing  a  corresponding  quantity  of 
a  metallic  salt  per  liter ;  finally,  a  clear  solution  of  1  part  of  gum 
arable  in  2  parts  of  water.  The  observations  were  made  in  the  fol- 
lowing manner : 
Two  quantities  of  10  cc.  of  the  solution  to  be  examined  were  run 
from  a  graduated  pipette  into  two  glasses  of  equal  volume  ;  with  one 
of  these  3  cc.  of  solution  of  gum  was  incorporated  by  stirring  and  to 
the  other  3  cc.  of  distilled  water  was  added ;  finally  10  cc.  of  sulphu- 
retted solution  was  added  to  each  and  rapidly  mixed.  The  following 
table  represents  what  was  observed  both  after  a  few  minutes  and  some 
weeks : 
Without  Gum. 
Black  preci Imitate, 
Black  precipitate,  . 
Black  preci])itate, 
Rosy  flesh-colored  pre 
cipitate. 
Black  precipitate, 
Black  precipitate, 
Lead  acetate, 
Silver  nitrate. 
Ferrous  sulphate, 
Manganous  sulptiate. 
Mercuric  chloride, 
Copper  sulphate, 
Zinc  sulphate, 
AntimonoLis  chloride 
in  solution  acidified 
byllCl. 
Arserious  acid,  . 
White  precipitate. 
Orange  precipitate. 
With  Gum. 
Clear  brown  solution. 
Clear  black  solution. 
Clear  black  solution. 
Clear  light  brown  solu- 
tion. 
Clear  dark  brown  solu- 
tion. 
Clear  dark  brown  solu- 
tion. 
Clear  colorless  solution 
Citron-yellow 
tate. 
precipi- 
Clear  citron-yellow  so- 
lution. 
