270 
Classification  of  Gums. 
Am.  Jour.  Pbarm. 
June,  1899. 
A  CLASSIFICATION  OF  GUMS,  RESINS  AND  SIMILAR 
SUBSTANCES. 
By  Frederick  I,.  IvEwton. 
The  terms,  "  gums,"  "  resins,"  and  "  similar  substances,"  as  here 
used,  include  only  those  plant  exudations  and  prepared  substances 
of  similar  appearance,  which  are  popularly  or  commercially  known 
as  gums,  resins,  balsams  or  rubbers. 
It  will  be  at  once  readily  seen  that  the  above  definition  excludes 
pectic  substances  and  numerous  gums,  resins  and  mucilages 
occurring  in  small  amounts  in  the  tissues  of  many  plants,  which 
should  find  a  place  in  a  complete  scientific  classification  of  resinous 
and  gummy  substances. 
The  classification  of  gums,  resins  and  similar  substances,  particu- 
larly those  included  by  the  commercial  world  under  the  general 
name  of  "  gums,"  presents  a  number  of  difficulties  which  probably 
account  tor  the  want  of  uniformity  among  the  different  systems  of 
classification  that  have  been  proposed  from  time  to  time.  This 
want  of  uniformity  is  no  doubt  due  to  the  fact  that  the  majority  of 
these  substances  are  complicated  bodies,  bearing  no  general  relation- 
ship as  regards  chemical  affinities,  and  are  widely  distributed  in  the 
vegetable  kingdom,  originating  therefrom  in  several  ways. 
Some  are  secretion  products,  others  have  been  clearly  proved  to 
be  formed  from  the  walls  of  plant  cells  by  chemical  metamorphosis, 
and  others  again  are  inspissated  saps  or  extracts. 
The  following  classification  is  based  chiefly  on  physical  properties 
and  chemical  composition  and  divides  these  substances  into  nine 
sections,  each  of  which  may  be  divided  into  a  number  of  sub- 
sections. 
SECTION  I.     TRUE  GUMS. 
Plant  exudations,  or  prepared  vegetable  substances,  which  dis- 
solve or  soften  in  cold  water,  forming  a  mucilage,  or  at  least  a 
liquid  of  a  gelatinous  consistency. 
They  are  insoluble  in  60  per  cent,  alcohol.  Treated  with  nitric 
acid,  they  yield  mucic  and  oxalic  acids.  Sulphuric  acid  converts 
them  into  dextrin  and  finally  into  sugar. 
They  may  be  divided  into  five  sub-sections  according  to  their 
chemical  composition. 
Sub-section  1.    Arabic  Group. — These  gums  consist  chiefly  of 
