Am*/a°^yi?9oarm'}  Decomposition  of  Chlorine-water  by  Light.  29 
ergo,  for  pararabin,  and  his  experiments  are  additional  evidence  to 
show  the  general  similarity  of  Sterculia  gums.  The  adhesiveness  of 
that  of  8.  Tragacantha  is  very  remarkable,  and  farther  information 
on  the  subject  is  desirable.  It  would  be  particularly  interesting  to 
know  the  percentage  of  arabin. 
Pararabin,  like  raetarabin,  is  of  course  a  modification  of  arabin. 
While  metarabin  is  converted  into  arabin  by  treatment  with  dilute 
alkali,  pararabin  is  similarly  converted  by  treatment  with  dilute  acid. 
They  both  are  insoluble,  but  swell  up  in  cold  water.  A  solution  of 
pararabin  in  weak  acid  is  precipitated  by  alkalis. 
Pararabin  is  usually  obtained  from  beet  or  carrot  pulp.  It  consti- 
tutes the  Chinese  vegetable  jelly  (agai-agai),  or  Ceylon  moss  (Gracil- 
aria),  according  to  Reichardt  (Watts'  "  Diet./'  3d  Supp.,  Pt.  1,  p. 
119;  Roscoe  and  Schorleminer,  iii,  2,  571).  The  present  writer 
took  a  sample  of  agar-agar,  together  with  a  Gracilaria  found  in  Aus  - 
tralian  waters,  and  a  sample  of  the  Japanese  "  kanten,"  said  to  be  ob- 
tained from  a  sea-weed  (Gelidium  corneum).  He  found  them  all  to 
consist  mainly  of  pararabin,  but,  unlike  Sterculia  gums,  and  like  traga- 
canth,  he  found  that  caustic  alkali  produced  a  canary -yellow  color 
when  boiled  with  them.  He  also  observed  (and  in  this  respect  these 
substances  differ  from  both  Sterculia  gum  and  tragacanth)  that  when 
baric  hydrate  is  added  in  the  cold  to  a  solution  in  weak  hydrochloric 
acid,  a  canary-yellow  color  was  produced  on  standing  for  a  few  hours. 
He  has  not  pursued  the  subject  further  in  this  paper,  as  being,  to  some 
extent,  a  digression. 
RATE  OF  DECOMPOSITION  OF  CHLORINE -WATER 
BY  LIGHT.1 
By  Dr.  G.  Gore,  F.  R.  S. 
In  this  research,  the  author  has  investigated,  by  means  of  the  vol- 
taic balance,  the  kind  and  amount  of  chemical  change,  the  rate  at 
which  decomposition  proceeds,  and  the  chemical  composition  of  the 
products  formed  at  all  stages  of  decomposition  of  chlorine-water  when 
exposed  to  daylight  and  sunlight  in  colorless  glass  vessels. 
The  chlorine-water,  by  exposure  to  diffused  daylight,  was  decom- 
posed with  moderate  uniformity,  but  at  a  gradually  diminishing  rate, 
1  Abstract  from  a  paper  read  before  the  Royal  Society ;  reprinted  from 
Chemical  News,  Dec.  6,  1889,  p.  271. 
