Dec.  i,  1892.] 
THE  TROPICAL  AGRICULTURIST. 
417 
BLEACHING  AND  BLEACHING  AGENTS. 
(Being  one  of  the  series  of  Marsh  Lectures,  deli- 
vered by  Mr.  C.  Brieberg,  Oct,  15th,  1892.) 
Bleaching  is  a very  ancient  art,  as  passages 
referring  to  it  in  the  earlier  sacred  and  profane 
writers  fully  testify.  It  had  probably  reached  a 
high  degree  of  excellence  among  the  inhabitants 
of  the  first  Assyrian  Empire,  and  was  certainly 
practised  in  Egypt  long  before  the  commence- 
ment of  written  history. 
In  Scripture  we  have  special  mention  of  “ fine 
linen,  white  and  clean.”  Herodotus  tells  us  that 
the  Babylonians  wore  “white  cloaks”;  and 
Athenaeus  makes  mention  of  “ Shining  fine  linen  ” 
as  opposed  to  that  which  was  “ raw  ” or  unbleached. 
At  this  early  period  and  for  many  centuries 
afterwards,  the  operations  of  washing,  fulling 
and  bleaching  were  not  distinctly  separated.  The 
common  system  of  washing  followed  by  drying 
in  the  sun  adopted  by  the  ancients,  by  frequent 
repetition,  decolourised  the  raw  materials  of  textile 
fabrics,  and  thus  must  no  doubt  have  taught 
them  the  art  of  natural  bleaching.  Washing  or 
steeping  in  ammoniacal  or  alkaline  lyes,  or  milk 
of  lime,  followed  by  exposure  to  tfie  sun,  formed 
the  chief  basis  of  their  system,  while  woollens, 
then  as  now,  were  treated  with  soap  and 
Fuller’s  earth,  potter’s  clay  or  like  argillaceous 
deposits. 
[The  use  of  lyes-like  that  of  “washing  soda  ” in 
modern  times — results  in  the  formation  of  a soap 
with  the  resinous  and  fatty  substances  naturally 
inherent  in  vegetable  fibres  or  communicated  to 
them  in  the  process  of  weaving ; v hile  Fuller’s 
earth  and  similar  natural  deposits  have  the 
property  of  extracting,  by  absorption,  the  fatty 
substances  present  in  wool.] 
We  read  that  in  the  time  of  Vespasian  (about 
60  a.d.)  and  undoubtedly  long  before  it,  cloths 
were  “ sulphured,”  and  according  to  Pliny, 
“sulphuring”  was  often  had  recourse  to  in 
ordinary  washing  as  well  as  in  the  bleaching 
process. 
Bleaching  continued  to  be  practised  with  no 
essential  change  of  its  principles,  until  the  dis- 
covery of  chlorine.  In  the  last  century  Holland  had 
a reputation  for  bleaching ; the  process  passed  next 
to  Ireland  and  Scotland,  and  thence  to  England. 
The  first  step  towards  the  modern  or  chemical 
system  of  bleaching  was  the  investigations  of 
Berthollet  on  chlorine  in  1784. 
The  knowledge  of  the  use  of  chlorine  as  a 
bleacher  was  soon  after  brought  to  Great  Britain 
and  practically  applied  in  Aberdeen,  and  about 
the  same  time  in  Glasgow,  from  whence  it  reached 
the  Manchester  manufacturers.  After  this  a 
number  of  patents  were  taken  out  for  various 
bleaching  liquors  and  powders  consisting  of  com- 
pounds or  mixtures  contaning  chlorine,  till  the 
new  and  “ continuous  process  of  bleaching,”  as  it 
is  called,  was  introduced  and  patented  about  1828 
The  term  bleaching  is  generally  understood  to 
mean  the  process  of  decolourising  cloth,  but  the 
word  may,  and  is  also  applied  to  the  whitening 
of  other  substances  as  well,  as  we  shall  see  later. 
In  this  paper,  therefore,  the  signification  of  the 
term  will  extend  not  only  to  the  decolourizing  of 
textile  fabrics  and  solid  bodies  alone,  but  also  to 
the  bleaching  or  removal  of  the  natural  colours 
of  any  substance. 
And  first,  I shall  notice  what  is  known  as  the 
“ natural  method  ” of  bleaching,  where  exposure 
to  light,  air  and  moisture  forms  the  leading  part 
of  the  process. 
The  simplest  form  of  natural  bleaching  is  to 
spread  out  the  ©loth  to  be  bleached  on  a grass 
53 
field  called  a “bleaching  green”  or  to  hang  it 
out  on  lines  in  the  open,  and  to  continue  sprinkling 
it  with  water  several  times  a day.  After  being 
exposed  for  a considerable  time  to  the  action  of 
air,  light  and  moisture,  the  cloth  is  rendered  white. 
The  process  is  necessarily  tedious,  and  occupies 
much  valuable  land  (not  to  speak  of  time),  and 
it  is  for  this  reason  that  in  past  days  much  of 
the  cloth  to  be  bleached  was  sent  over  from 
England  to  Holland.  A particular  kind  of  cloth 
which  was  regularly  sent  to  Holland  received  on 
that  account  the  name  of  “ Holland  ” ; and  another 
kind  of  linen  which,  owing  to  its  fineness,  was 
spread  on  the  better  grass-fields  or  lawns,  received 
the  appellation  of  “ Lawn.” 
Let  us  now  enquire  into  the  chemistry  of 
this  the  simplest  form  of  bleaching.  Till  com- 
paratively recent  times  it  was  thought  that  the 
only  agent  in  the  natural  mode  of  bleaching 
was  resident  in  the  sun’s  rays.  Chemical  change, 
both  of  combination  and  decomposition,  but  more 
particularly  the  latter,  can  be  effected  by  the 
action  of  light,  and  many  instances  of  this  may 
be  cited.  Such  change  is  chiefly  produced  by 
certain  invisible  rays  which  accompany  the 
luminous  rays  of  the  sun,  though  the  latter  also 
under  certain  circumstances  exert  similar  powers. 
The  chemically  acting  rays  are  sometimes  called 
“actinic”  rays,  and  the  peculiar  agency  or 
principle  associated  with  light  and  heat  in  the 
sun’s  rays,  and  upon  which  their  chemical  power 
depends  is  known  as  actinism.  This  power  was  first 
discovered  by  M.  Berard  in  1812.  It  is  essential 
to  the  growth  and  development  of  all  the  higher 
orders  of  plants,  and  to  the  existence  of  healthy 
animal  life.  But  the  discovery  of  the  substance 
called  ozone,  which  possesses  powerful  bleaching 
properties,  and  which  in  greater  or  less  quantities 
exists  in  the  atmosphere  of  country  districts,  led 
to  the  opinion  now  held  by  chemists  that  the 
bleaching  which  takes  place  when  cloth  is 
moistened  and  exposed  to  the  air  is  mainly  due  to 
the  ozone  present  in  the  atmosphere,  and  this 
is  proved  by  the  fact  that  in  town  districts, 
where  little  or  no  ozone  exists,  cloth  is  never  able 
to  be  bleached  perfectly  white. 
Ozone,  which  is  a gas,  was  discovered  by 
Schonbein  of  Basle,  and  when  first  identified  was 
supposed  to  be  a new  elementary  principle 
analogous  to  chlorine,  but  is  now  known  to  b© 
oxygen  in  a second  or  allotropic  state — ozonized 
oxygen  as  it  is  sometimes  called — in  which  it 
exhibits  increased  activity  and  new  properties. 
Eoscoe  describes  ozone  as  oxygen  in  a condensed 
state,  being  1J  times  as  heavy  as  oxygen';  that 
is,  3 volumes  of  oxygen  condense  into  2 volumes 
of  ozone.  Thus  the  molecular  formula  of  oxygen 
being  O2,  that  of  ozone  would  be  represented  by  O3'. 
Ozone  can  be  prepared  artificially  by  hanging 
a piece  of  phosphorus  in  a bottle  filled  with 
moist  air,  or  by  the  action  of  strong  sulphuric 
acid  on  permanganate  of  potash  (a  substance 
which  in  the  form  of  a solution  is  familiar  as 
“Condy’s  Fluid”).  Ozone  is,  however,  largely 
produced  in  Nature  by  electric  discharges  which 
occur  during  thunderstorms,  and  the  credit  of 
purifying  the  air  commonly  attributed  to  “ thunder 
and  lightning  ” must  be  given  to  ozone.  This 
same  substance  is  of  the  utmost  importance 
in  the  plant  economy  as  helping  to  form  the  higher 
compounds  of  nitrogen  for  the  nutrition  of 
plants.  Ozone  derives  its  name  from  the  strong 
and  peculiar  metallic  odour  which  characterizes 
it.  Of  course  its  artificial  preparation  is  of  no 
practical  value,  and  in  fact  it  would  be  almost 
impossible  to  perceive  it  in  a room  full  of 
people,  .Besides,  as  I have  indicated,  it  i^  the  frqq 
