18 
REMARKS  ON  GUM  MEZQUITE. 
contact  with  water  the  gum  dissolves  as  completely  as  the  purest 
gum  arabic,  without  any  tendency  to  swell  like  cherry  gum  or  tra- 
gacanth ;  and  this  is  true  of  the  dark  colored  pieces  as  well  as 
the  light,  the  mucilage  being  perfectly  transparent.  The  solu- 
tion has  a  slightly  acid  reaction  ;  alcohol  precipitates  it  in  white 
flocks  like  arabin ;  neither  neutral  or  basic  acetate  of  lead  alone 
precipitates  it,  but  on  the  addition  of  ammonia  after  the  neutral 
acetate,  a  bulky  gelatinous  precipitate  is  thrown  down.  This 
does  not  occur  when  the  ammonia  is  added  after  the  subacetate. 
When  the  gum  is  boiled  with  an  alkaline  solution  of  oxide  of 
copper,  no  reduction  occurs  indicative  of  glucose.  When  pow- 
dered borax  is  added  to  its  solution  no  coagulation  occurs,  as 
with  arabin,  nor  does  tersulphate  of  iron  occasion  any  precipitate. 
Oxalate  of  ammonia  instantly  causes  a  white  cloud  in  the  trans- 
parent solution  ;  iodine  occasions  no  change.  Concentrated  sul- 
phuric acid  dissolves  it,  and  when  heated  chars  it. 
When  heated  in  nitric  acid  till  effervescence  ceases,  it  affords 
mucic  and  oxalic  acids,  like  ordinary  gum  ;  exposed  to  a  red  heat 
it  swells  up,  burns,  and  leaves  a  bulky  greyish- white  ash,  amount- 
ing to  2.1  per  cent,  of  the  gum  heated.  This  ash  consists  of 
soluble  potash  salts,  (carbonate,  sulphate,  and  chloride)  and  in- 
soluble lime  salts. 
From  the  above  results  it  is  evident  that  gum  mezquite  is  not 
identical  with  true  gum  arabic.  Its  solubility  is  quite  equal  to 
that  gum,  and  is  greater  than  several  varieties,  which  is  an  im- 
portant feature  in  the  American  product.  The  mucilage  it 
yields  is  like  the  syrupy  mucilage  of  dextrine,  and  has  similar 
adhesive  properties.  In  its  reactions  writh  nitric  and  sulphuric 
acids,  with  alcohol,  and  with  oxalate  of  ammonia,  it  resembles 
arabin,  but  in  reference  to  basic  acetate  of  lead,  borax,  and  the 
sulphate  of  iron,  it  is  entirely  different  from  arabin  or  any  of  the 
gums  described  that  I  am  acquainted  with. 
It  is  to  be  regretted  that  Dr.  Shumard  has  made  no  allusion 
to  the  botanical  origin  of  this  gum,  a  point  on  which  he  must 
certainly  have  informed  himself.  There  are  several  species  of 
acacia  indigenous  to  that  region,  and  botanists  here  believe  it  is 
probably  attributable  to  one  or  more  of  these.  Its  abundance 
and  easiness  of  collection,  if  corroborated  in  practice,  may  prove 
important  hereafter,  as  an  addition  to  our  internal  national  re- 
