30  Decomposition  of  Chlorine-water  by  Light.  {Am\££fwi£.arm' 
as  shown  by  the  losses  of  voltaic  energy,  until  no  further  loss  of  such 
energy  occurred ;  the  liquid  then  consisted  of  an  aqueous  solution  of 
hydrochloric  acid,  hydrochlorous  acid,  and  chloric  acid.  By  further 
exposure  of  the  liquid  to  daylight  and  sunlight  during  several  weeks, 
peroxide  of  hydrogen  was  formed,  and  the  amount  of  hydrochloric 
acid  and  voltaic  energy  very  slowly  increased  until  that  of  the  latter 
became  equal  to  that  of  dilute  hydrochloric  acid  of  equivalent  strength 
to  the  whole  of  the  chlorine  present ;  all  the  other  chief  properties  of 
the  final  liquid  agreed  with  those  of  a  mixture  of  dilute  hydrochloric 
acid  and  peroxide  of  hydrogen.  Still  further  exposure  to  strong  sun- 
light caused  no  further  change  in  chemical  composition,  amount  of 
voltaic  energy,  or  other  property  of  the  liquid. 
This  research  shows  distinctly  that  the  decomposition  of  chlorine- 
water  by  light  may  be  divided  into  two  essentially  different  parts,  or 
periods,  of  chemical  change,  and  that  the  kinds  of  chemical  change 
occurring  during  these  two  periods  are  largely  different .  During  the 
first  period,  a  very  great  and  gradual  loss  of  voltaic  energy  occurs, 
attended  by  formation  of  hydrochloric,  hydrochlorous,  and  chloric 
acids.  During  the  second  period,  a  moderate  and  very  slow  increase 
of  voltaic  energy  takes  place,  accompanied  by  decomposition  of  the 
hydrochlorous  and  chloric  acids ;  a  further  formation  of  hydrochloric 
acid,  and  the  production  of  peroxide  of  hydrogen.  Under  the  influ- 
ence of  prolonged  sunlight,  the  whole  of  the  oxygen  of  the  hydro- 
chlorous and  chloric  acids  united  with  water  to  form  peroxide  of  hy- 
drogen, and  the  peroxide  then  combined  with  the  whole  of  the  hydro- 
chloric acid  to  form  a  definite  "  solution  compound,"  represented  by 
the  formula  2HC1.H202- 
The  chemical  composition  of  the  products  of  the  chauge  at  the  end 
of  the  first  and  second  periods  were  ascertained  by  means  of  the 
voltaic  balance  and  ordinary  chemical  analysis.  During  the  first 
period,  forty  consecutive  measurements  of  the  voltaic  energy,  at 
stated  intervals  of  time,  were  made,  and  the  energy  diminished  from 
about  1,219  millions  to  2*9  millions  ;  and  during  the  second  period 
eight  such  measurements  were  made,  and  the  energy  increased  to  9*3 
millions,  A  curve  is  given  showing  the  rate  of  loss  of  energy  dur- 
ing the  first  period. 
It  is  interesting  to  observe  that  suitably  decomposed  chlorine-water, 
or  possibly,  in  its  stead,  a  mixture  of — 
6HCI+HCIO+HCIO3 
