﻿486 
  Transactions. 
  —Chemistry. 
  

  

  This 
  tlieory 
  lias 
  been 
  combated 
  by 
  eminent 
  scientists, 
  as 
  will 
  shortly 
  

   appear 
  ; 
  but 
  wlietlier 
  it 
  be 
  true 
  or 
  not, 
  it 
  is 
  certain 
  that 
  the 
  mode 
  of 
  action 
  

   of 
  such 
  salts 
  is 
  quite 
  different 
  to 
  that 
  by 
  which 
  alum 
  is 
  always 
  supposed 
  to 
  

   operate, 
  although 
  they 
  have 
  been, 
  for 
  want 
  of 
  due 
  consideration, 
  undis- 
  

   tinguished 
  from 
  each 
  other. 
  It 
  is, 
  moreover, 
  certain 
  that 
  clay, 
  so 
  coagu- 
  

   lated, 
  is 
  de-hydrated, 
  and 
  the 
  knowledge 
  of 
  the 
  two 
  cognate 
  facts 
  — 
  - 
  

   simultaneous 
  coagulation 
  and 
  dehydration 
  of 
  clay 
  under 
  such 
  circumstances 
  

   — 
  is, 
  as 
  will 
  shortly 
  be 
  seen, 
  one 
  step 
  towards 
  the 
  solution 
  of 
  the 
  question 
  

   before 
  us 
  (the 
  cause 
  of 
  the 
  persistent 
  suspension 
  of 
  clay 
  in 
  certain 
  water), 
  

   as 
  it 
  is 
  thereby 
  shown 
  that 
  clay 
  must 
  be 
  hydrated 
  to 
  an 
  extent 
  at 
  about 
  its 
  

   maximum 
  in 
  order 
  to 
  manifest 
  this 
  ^Jroperty. 
  

  

  Induced 
  by 
  a 
  knowledge 
  of 
  thjs 
  fact, 
  I 
  ventured 
  (in 
  the 
  communication 
  

   referred 
  to) 
  in 
  explanation 
  of 
  this 
  persistent 
  suspension, 
  the 
  opinion 
  that 
  

   clay 
  can 
  hydrate 
  to 
  an 
  indefinite 
  extent, 
  so 
  that 
  it 
  can 
  even 
  take 
  up 
  in 
  a 
  

   combined 
  form 
  the 
  whole 
  of 
  the 
  water 
  in 
  which 
  it 
  may 
  be 
  diffused, 
  making 
  

   a 
  kind 
  of 
  jelly 
  with 
  it, 
  very 
  weak 
  but 
  still 
  having 
  enough 
  consistence 
  to 
  

   retain 
  in 
  a 
  comparatively 
  fixed 
  state 
  the 
  clay 
  particles 
  of 
  which 
  it 
  is 
  in 
  part 
  

   composed. 
  But 
  having 
  lately 
  taken 
  careful 
  cognizance 
  of 
  the 
  remarkable 
  

   fact 
  that 
  particles 
  of 
  clay 
  when 
  persistently 
  in 
  suspension 
  are 
  as 
  persistently 
  

   in 
  motion 
  (describing 
  the 
  so-named 
  Browinian 
  movements), 
  I 
  have 
  now 
  

   perceived 
  that 
  hydration 
  of 
  clay 
  never 
  does 
  occur 
  to 
  this 
  extent 
  ; 
  these 
  

   movements 
  of 
  such 
  particles 
  proving 
  the 
  presence 
  of 
  free 
  water 
  in 
  their 
  

   neighbourhood, 
  which, 
  of 
  course, 
  is 
  against 
  the 
  theory 
  of 
  indefinite 
  hydra- 
  

   tion, 
  and 
  so 
  left 
  the 
  question 
  as 
  to 
  this 
  persistent 
  suspension 
  of 
  clay 
  still 
  to 
  

   me 
  unsolved. 
  

  

  Upon 
  casting 
  about 
  in 
  our 
  scientific 
  works 
  and 
  periodicals 
  for 
  a 
  solution 
  

   of 
  this 
  phenomenon, 
  I 
  came 
  across 
  various 
  theories 
  professing 
  to 
  account 
  for 
  

   it. 
  Notably, 
  one 
  by 
  Prof. 
  Jevons, 
  ascribing 
  it 
  to 
  electricity 
  ; 
  one 
  by 
  Dr, 
  

   Hunt, 
  ascribing 
  it 
  to 
  the 
  viscidity 
  or 
  cohesiveness 
  of 
  pure 
  water 
  ; 
  and 
  

   another 
  by 
  Mr. 
  Dancer, 
  who 
  attributes 
  it 
  to 
  the 
  effect 
  of 
  heat 
  unevenly 
  

   distributed. 
  Upon 
  mature 
  deliberation 
  I 
  concluded 
  that 
  each 
  of 
  these 
  

   theories 
  is 
  as 
  unsound 
  as 
  the 
  one 
  which 
  I 
  had 
  discarded, 
  and 
  it 
  then 
  

   occurred 
  to 
  me 
  that 
  in 
  the 
  action 
  of 
  Osomose 
  we 
  have 
  the 
  solution 
  sought 
  

   for, 
  i.e., 
  the 
  cause 
  of 
  the 
  persistent 
  suspension 
  of 
  clay, 
  and 
  after 
  a 
  careful 
  

   consideration 
  of 
  this 
  view 
  of 
  the 
  case, 
  I 
  am 
  so 
  impressed 
  with 
  the 
  idea 
  of 
  

   its 
  accuracy 
  that 
  I 
  now 
  venture 
  to 
  submit 
  it 
  for 
  your 
  criticism. 
  

  

  In 
  order 
  to 
  present 
  this 
  view 
  to 
  you 
  in 
  as 
  favourable 
  and 
  clear 
  a 
  light 
  as 
  

   possible, 
  I 
  will 
  first 
  briefly 
  state 
  the 
  princij)les 
  of 
  Osomose. 
  

  

  Any 
  colloid 
  (that 
  is, 
  a 
  substance 
  which 
  cannot 
  be 
  crystallized, 
  and 
  

   which, 
  though 
  insoluble 
  in 
  water, 
  is 
  capable 
  of 
  largely 
  combining 
  with 
  

   it) 
  has 
  the 
  property 
  of 
  allowing 
  water 
  to 
  pass 
  through 
  it, 
  and 
  crystalloids 
  

  

  