Am.  Jour.  Pharm. 
June,  1889. 
Humous  Substances. 
309 
I  have  not  yet  been  able  to  try  how  far  this  iodine  absorption  pro- 
cess would  serve  as  a  means  of  estimating  the  amount  of  oil  in  aroma- 
tized waters.  It  seems  feasible  to  shake  up  a  known  amount  of  the 
water  with  a  little  chloroform,  and  to  digest  the  chloroformic  solution 
with  the  Hiibl  reagent,  but  at  present,  so  far  as  I  know,  it  has  not 
been  tried  for  this  purpose. 
In  conclusion,  I  regret  that  this  account  is  so  much  less  complete 
than  I  had  hoped  to  make  it.  The  facts  that  the  subject  is  of  some 
interest  to  members  of  this  Society,  and  that  the  present  is  the  last 
meeting  for  this  session,  will,  I  trust,  serve  to  excuse  my  presenting  it 
in  this  incomplete  form. 
My  thanks  are  due  in  particular  to  Messrs.  Stafford,  Allen  &  Sons, 
for  the  very  fine  series  of  oils  they  have  furnished  me  with  ;  also  to 
Messrs.  Geo.  Atkinson  and  Sons.  J.  and  R.  Y.  Matthew,  of  Croydon, 
Messrs.  Stevenson  and  Howell,  Mr.  Samuel  Lambert,  Mr.  J.  Moss, 
Mr.  R.  Morrison,  and  to  Mr.  Thomas  Hunter  for  his  able  assistance 
in  this  investigation. 
HUMOUS  SUBSTANCES.1 
By  F.  Hoppe-Seyler. 
On  the  death  of  plants  or  parts  of  plants,  substances  of  a  brown 
color  are  formed  which  are  called  humous  substances.  Wood,  how- 
ever, often  remains  white  for  years.  In  dry  air,  or  at  a  high  tem- 
perature, plants  can  be  dried  without  browning.  The  browning  of  the 
surface  of  a  cut  apple  may  be  taken  as  a  very  rapid  example  of  the 
process.  Bacteria  do  not  seem  to  be  concerned  in  this  change.  This 
brown  coloration  does  not  occur  to  any  extent  in  dead  animal  tissues. 
It  is  not,  however,  due  to  the  chlorophyll  of  plants,  as  it  occurs 
equally  quickly  in  plants  which  contain  no  chlorophyll.  The  almost 
universal  distribution  of  tannic  acid  and  carbohydrates,  and  especially 
of  cellulose,  suggests  that  these  may  be  sources  of  the  humous  sub- 
stance, or  it  may  come  from  the  hydrocyanic  acid,  phenol,  and  nitro- 
genous compounds  of  plant  tissues. 
Pure  cellulose  when  mixed  with  mud  containing  micro-organisms, 
ferments  and  yields  carbonic  anhydride  and  methane  in  the  absence  of 
oxygen,  but  no  humous  substance  is  formed  ;  in  the  presence  of  oxy- 
gen, the  cellulose  (filter-paper)  still  remains  quite  white;  all  sorts  of 
lZeit.  physioL  Chem.,  xiii.,  66—121;  reprinted  from  Jour.  Chem.  Soc,  1889, 
p.  285. 
