COMPOSITION  OF  VEGETABLE  GUMS. 
367 
earths,  it  immediately  dissolves  and  undergoes  another  modifi- 
cation ;  for  acids  do  not  precipitate  it  from  the  solution.  The 
new  body,  therefore,  now  in  combination  with  the  base,  is  termed 
Grummie  Acid.  M.  Fremy  states  that  he  has  studied  this  ac- 
tion of  bases  on  metagummic  acid  with  the  greatest  care,  and 
he  finds  the  resulting  compound  to  present  all  the  characters  of 
gum  arabic.  These  experiments  tend  then  to  cause  us  to  entire- 
ly alter  our  ideas  of  the  nature  of  the  gums.  Instead  of  regard- 
ing gum  as  a  neutral  body,  somewhat  analogous  to  dextrine,  it 
must  be  considered  as  derived  from  a  principle,  metagummic 
acid,  insoluble  in  water,  which  under  the  influence  of  bases  be- 
comes soluble,  is  converted  into  gummic  acid,  and  in  combina- 
tion, generally  with  lime,  forming  a  veritable  salt,  constitutes 
ordinary  soluble  gum.  To  confirm  this  view,  M.  Fremy  care- 
fully examined  natural  gum.  It  was  previously  known  that 
gum  cannot,  in  any  case,  be  purified  from  the  inorganic  bodies 
which  it  contains,  and  that,  upon  calcination,  it  always  leaves  a 
calcareous  ash  amounting  to  3  or  4  per  cent.  Moreover,  mu- 
cilage always  furnishes  a  precipitate  with  oxalate  of  ammonia. 
When  solution  of  gum  is  treated  with  subacetate  of  lead,  an  in- 
soluble compound  is  formed,  and  under  these  circumstances  the 
lime  is  separated  from  the  organic  acid,  and  remains  in  solution 
combined  with  acetic  acid.  When  metagummic  acid  is  boiled 
with  lime,  a  soluble  substance  is  obtained  identical  with  gum 
arabic ;  it  is  neutral,  insipid,  uncrystallizable,  soluble  in  water, 
and  precipitated  by  alcohol  and  subacetate  of  lead  ;  calcined,  it 
leaves  an  ash,  amounting  to  3  per  cent.,  like  gum  arabic. 
All  these  facts  demonstrate  that  gum  is  really  a  compound  of 
lime  with  an  organic  acid,  and  not  an  immediate  neutral  princi- 
ple. By  the  action  of  oxalic  acid  the  lime  may  be  separated 
from  gum,  without  the  production  of  metagummic  acid.  This 
transformation  may,  however,  be  then  readily  effected  by  the 
application  of  heat.  M.  Ge*lis  has  made  an  interesting  observa- 
tion on  gum  arabic.  He  found  that  by  a  temperature  of  150° 
cent.,  sustained  for  many  hours,  gum  becomes  insoluble  in 
water,  but  that  by  subsequent  prolonged  boiling  it  passes  back 
again  to  the  state  of  ordinary  gum.  Under  these  circumstances 
no  elimination  of  lime  takes  place,  but  the  gum  or  gummate  of 
lime  undergoes  an  isomeric  modification,  and  metagummate  of 
