310 
Humous  Substances. 
Am,  Jour.  Pfcarm. 
June,  1889. 
mud  being  used  in  the  experiments.  By  heating  with  water  at  188— 
200°,  or  with  caustic  alkalis,  humous  substances  are  formed.  Water 
in  glass  tubes  produced  a  brown  residue,  and  the  liquid  was  found  to 
contain  formic  acid,  catechol,  and  protocatechuic  acid  ;  when  platinum 
tubes  were  employed,  there  was  a  brown  residue,  but  the  other  pro- 
ducts obtained  in  glass  tubes  were  absent,  as  they  are  due  to  the  de- 
composition of  the  humous  substance  produced  by  a  small  quantity  of 
alkali,  dissolved  out  from  the  glass  at  the  high  temperature  to  which 
the  tubes  were  subjected.  Other  experiments  were  performed  with 
strong  alkalis,  and  the  resulting  gases,  as  well  as  the  residue,  were 
analyzed. 
The  fermentation  of  wood-gum  was  found  to  be  similar  to  that  of 
cellulose  ;  and  it  is  supposed  that  the  lignic  acid  may  be  instrumental 
in  the  formation  of  humous  substances  in  turf,  peat,  etc. 
Tannin  red,  obtained  from  certain  plants  by  extracting  with  water, 
and  the  phlobaphen  of  Stahelin  and  Hofstetter,  an  amorphous  brown 
substance,  are  apparently  derivatives  of  tannic  acid,  and  may  be  in- 
cluded under  humous  substances.  The  preparation  and  properties  of 
a  large  number  of  these  substances  are  described.  They  are  formed 
by  the  action  of  alkalis  on  various  carbohydrates  (dextrose,  lactose, 
cane-sugar,  glycuronic  acid,  etc.)  ;  from  various  aromatic  substances ; 
and  those  obtained  from  various  vegetable  sources  are  also  described. 
They  are  amorphous,  differing  in  percentage  composition,  mostly  con- 
taining nothing  but  carbon,  hydrogen,  and  oxygen.  A  few  contain 
nitrogen,  like  those  described  by  Udanszky  (1887)  in  urine.  A  de- 
rivative of  humous  substances  called  humic  acid  is  described,  and  var- 
ious names  are  given  to  various  other  members  of  the  group. 
The  original  paper  must  be  consulted  for  details  concerning  their 
preparation  and  analysis ;  the  following  summary  will,  however,  in- 
dicate the  methods  adopted  in  their  separation : 
Humous  substances  fall  into  three  groups :  the  first  includes  those 
which  are  soluble  neither  in  caustic  alkalis  nor  in  alcohol,  but  unite 
with  alkalis,  forming  a  slimy  mass.  This  group  includes  the  humin 
and  ulmin  of  Mulder.  The  second  group  consists  of  those  which  are 
completely  soluble  in  alkalis,  and  precipitable  from  such  solutions  by 
acids ;  the  precipitate  formed  is  voluminous  and  jelly-like,  and  is  in- 
soluble in  alcohol.  A  part  of  the  tannin  reds,  and  of  humic  and  ulmie 
acids,  belong  to  this  group.  The  substances  in  the  third  group  re- 
semble those  in  the  second  with  regard  to  their  solubility  in  alkalis ; 
