﻿1875.] 
  On 
  Attraction 
  and 
  Repulsion 
  from 
  Radiation. 
  373 
  

  

  IV. 
  

  

  When 
  a 
  simple 
  salt 
  assumes 
  one 
  or 
  more 
  definite 
  states 
  of 
  hydration 
  at 
  

   different 
  temperatures 
  below 
  100° 
  C, 
  the 
  hydrated 
  compounds 
  A 
  and 
  B 
  

   will 
  be 
  successively 
  produced 
  in 
  the 
  liquid 
  state 
  if 
  a 
  saturated 
  solution 
  of 
  

   the 
  original 
  salt 
  be 
  heated 
  to 
  100° 
  C. 
  ; 
  or, 
  in 
  other 
  words, 
  the 
  chemical 
  

   constitution 
  of 
  the 
  liquid 
  is 
  altered 
  so 
  that, 
  as 
  higher 
  temperatures 
  are 
  

   attained, 
  it 
  becomes 
  a 
  solution 
  of 
  substance 
  A 
  or 
  of 
  substance 
  B, 
  at 
  

   intermediate 
  temperatures 
  mixtures 
  of 
  these. 
  

  

  y. 
  

  

  The 
  action 
  of 
  heat 
  on 
  the 
  violet 
  hydrated 
  compounds 
  of 
  chromium 
  is 
  

   not 
  simply 
  a 
  dissociation 
  of 
  water-molecules 
  or 
  of 
  acid 
  from 
  base, 
  but 
  a 
  

   true 
  decomposition, 
  resulting 
  in 
  the 
  production 
  of 
  a 
  different 
  class 
  of 
  

   salts 
  with 
  different 
  generic 
  properties. 
  

  

  Many 
  new 
  salts 
  were 
  prepared 
  for 
  this 
  work, 
  and 
  others 
  were 
  examined 
  

   with 
  greater 
  care 
  than 
  had 
  previously 
  been 
  bestowed 
  on 
  them; 
  from 
  

   these 
  substances, 
  indeed, 
  the 
  most 
  important 
  part 
  of 
  the 
  results 
  were 
  

   derived. 
  

  

  II. 
  " 
  On 
  Attraction 
  and 
  Repulsion 
  resulting 
  from 
  Radiation/'' 
  — 
  

   Part 
  II. 
  By 
  William 
  Crookes, 
  F.R.S. 
  &c. 
  Received 
  

   March 
  20, 
  1875. 
  

  

  (Abstract.) 
  

  

  This 
  is 
  the 
  second 
  part 
  of 
  a 
  paper 
  which 
  the 
  author 
  sent 
  to 
  the 
  Royal 
  

   Society 
  in 
  August 
  1873. 
  The 
  author 
  commences 
  by 
  describing 
  improve- 
  

   ments 
  which 
  he 
  has 
  made 
  in 
  the 
  Sprengel 
  pump, 
  and 
  in 
  various 
  acces- 
  

   sories 
  which 
  are 
  necessary 
  when 
  working 
  at 
  the 
  highest 
  rarefactions. 
  

  

  Continuing 
  the 
  description 
  of 
  apparatus, 
  the 
  author 
  describes 
  different 
  

   new 
  forms 
  which 
  enable 
  the 
  phenomena 
  of 
  repulsion 
  by 
  radiation 
  to 
  be 
  

   observed 
  and 
  illustrated. 
  A 
  bulb 
  3 
  inches 
  in 
  diameter 
  is 
  blown 
  at 
  the 
  end 
  

   of 
  a 
  glass 
  tube 
  18 
  inches 
  long. 
  In 
  this 
  bulb 
  a 
  fine 
  glass 
  stem, 
  with 
  a 
  

   sphere 
  or 
  disk 
  of 
  pith 
  &c. 
  at 
  each 
  end, 
  is 
  suspended 
  by 
  means 
  of 
  a 
  cocoon- 
  

   fibre. 
  The 
  whole 
  is 
  attached 
  to 
  the 
  Sprengel 
  pump 
  in 
  such 
  a 
  way 
  that 
  

   it 
  can 
  be 
  perfectly 
  exhausted 
  and 
  then 
  hermetically 
  sealed. 
  Besides 
  pith, 
  

   the 
  terminals 
  may 
  be 
  made 
  of 
  cork, 
  ivory, 
  metal, 
  or 
  other 
  substance. 
  

   During 
  exhaustion 
  several 
  precautions 
  have 
  to 
  be 
  taken, 
  which 
  are 
  fully 
  

   entered 
  into 
  in 
  the 
  paper. 
  To 
  get 
  the 
  greatest 
  delicacy 
  in 
  an 
  apparatus 
  

   of 
  this 
  kind, 
  there 
  is 
  required 
  large 
  surface 
  with 
  a 
  minimum 
  of 
  weight. 
  

   An 
  apparatus 
  constructed 
  with 
  the 
  proper 
  precautions 
  is 
  so 
  sensitive 
  to 
  

   heat, 
  that 
  a 
  touch 
  with 
  the 
  finger 
  on 
  a 
  part 
  of 
  the 
  globe 
  near 
  one 
  extre- 
  

   mity 
  of 
  the 
  pith 
  will 
  drive 
  the 
  index 
  round 
  over 
  90°, 
  whilst 
  it 
  follows 
  a 
  

  

  2g2 
  

  

  