﻿456 
  Mr. 
  Wilson 
  on 
  the 
  Influence 
  of 
  Dissolved 
  Substances 
  

  

  The 
  pressure 
  of 
  the 
  air 
  was 
  indicated 
  by 
  the 
  mercury 
  

   manometer 
  M, 
  and 
  was 
  usually 
  30 
  cms. 
  The 
  air 
  could 
  be 
  

   saturated 
  with 
  moisture 
  if 
  necessary 
  by 
  gently 
  warming 
  water 
  

   in 
  the 
  flask 
  W. 
  The 
  spray 
  was 
  projected 
  into 
  a 
  four-necked 
  

   globe 
  Gr, 
  which 
  also 
  contained 
  the 
  solution 
  being 
  sprayed. 
  

   The 
  spray 
  given 
  by 
  this 
  sprayer 
  was 
  very 
  abundant 
  and 
  fine, 
  

   and 
  formed 
  a 
  cloud 
  which 
  did 
  not 
  settle 
  for 
  a 
  considerable 
  

   time. 
  

  

  The 
  air 
  containing 
  the 
  cloud 
  was 
  bubbled 
  through 
  sulphuric 
  

   acid 
  in 
  the 
  two 
  wash-bottles, 
  and 
  then 
  through 
  water 
  in 
  the 
  

   flask 
  F. 
  The 
  rate 
  of 
  bubbling 
  was 
  regulated 
  at 
  the 
  outlet- 
  

   tube 
  T, 
  where 
  most 
  of 
  the 
  air 
  was 
  allowed 
  to 
  escape. 
  

  

  On 
  spraying 
  distilled 
  or 
  tap-water 
  no 
  cloud 
  could 
  be 
  detected 
  

   in 
  F 
  usually, 
  though 
  sometimes 
  a 
  very 
  faint 
  cloud 
  appeared. 
  

   If 
  a 
  dilute 
  solution 
  of 
  sulphuric 
  acid 
  was 
  sprayed, 
  then 
  a 
  

   cloud 
  appeared 
  over 
  the 
  water 
  in 
  F. 
  If 
  the 
  air 
  from 
  which 
  

   the 
  dilute- 
  acid 
  cloud 
  had 
  been 
  removed 
  by 
  bubbling 
  through 
  

   the 
  sulphuric 
  acid 
  was 
  collected 
  in 
  a 
  dry 
  flask, 
  no 
  cloud 
  could 
  

   be 
  detected 
  in 
  it; 
  but 
  on 
  adding 
  a 
  little 
  water 
  and 
  shaking 
  

   gently 
  so 
  as 
  to 
  saturate 
  the 
  air 
  in 
  the 
  flask 
  with 
  moisture, 
  a 
  

   cloud 
  was 
  formed. 
  This 
  occurred 
  even 
  if 
  the 
  dry 
  flask 
  con- 
  

   taining 
  the 
  air 
  was 
  allowed 
  to 
  stand 
  for 
  half 
  an 
  hour 
  before 
  

   the 
  w 
  ? 
  ater 
  was 
  put 
  in 
  it. 
  One 
  gram 
  of 
  H 
  2 
  S0 
  4 
  in 
  a 
  litre 
  of 
  

   water 
  produced 
  a 
  dense 
  cloud. 
  

  

  Dilute 
  solutions 
  of 
  H 
  3 
  P0 
  4 
  , 
  KOH, 
  CaCl 
  2 
  , 
  NaCl, 
  K 
  2 
  C0 
  3 
  , 
  

   sugar, 
  and 
  glycerine 
  all 
  gave 
  a 
  similar 
  effect, 
  and 
  the 
  presence 
  

   of 
  the 
  alkali 
  metals 
  in 
  the 
  cloud 
  could 
  be 
  easily 
  shown 
  by 
  

   passing 
  it 
  into 
  a 
  bunsen 
  flame. 
  The 
  solutions 
  when 
  made 
  up 
  

   so 
  as 
  to 
  contain 
  equal 
  numbers 
  of 
  molecules 
  of 
  the 
  dissolved 
  

   substance 
  per 
  litre 
  gave 
  apparently 
  about 
  equally 
  dense 
  

   clouds. 
  A 
  considerable 
  change 
  in 
  the 
  strength 
  of 
  a 
  solution 
  

   was, 
  however, 
  necessary 
  to 
  produce 
  a 
  sensible 
  change 
  in 
  the 
  

   density 
  of 
  the 
  cloud. 
  

  

  A 
  solution 
  of 
  potassium 
  uranium 
  sulphate 
  gave 
  a 
  similar 
  

   cloud 
  in 
  F, 
  as 
  also 
  all 
  other 
  solutions 
  of 
  non-volatile 
  sub- 
  

   stances 
  we 
  tried. 
  Dilute 
  hydrochloric 
  acid 
  gave 
  no 
  cloud 
  in 
  

   F 
  unless 
  the 
  solution 
  contained 
  about 
  5 
  per 
  cent, 
  or 
  more 
  of 
  

   HC1, 
  when 
  a 
  cloud 
  appeared, 
  no 
  doubt 
  due 
  simply 
  to 
  dry 
  

   HC1 
  gas 
  entering 
  F. 
  Acetic 
  acid 
  solutions 
  gave 
  no 
  cloud 
  in 
  F. 
  

   The 
  explanation 
  of 
  the 
  re-formation 
  of 
  the 
  cloud 
  in 
  F 
  is 
  

   evidently 
  very 
  simple. 
  The 
  small 
  drops 
  of 
  solution 
  forming 
  

   the 
  original 
  cloud 
  evaporate 
  to 
  the 
  sulphuric 
  acid, 
  and 
  minute 
  

   particles 
  of 
  salt 
  or 
  other 
  substance 
  remain 
  which 
  are 
  too 
  small 
  

   to 
  form 
  a 
  visible 
  cloud. 
  These 
  particles 
  on 
  coming 
  into 
  a 
  

   moist 
  atmosphere 
  condense 
  w 
  7 
  ater 
  on 
  themselves, 
  re-forming 
  

   the 
  visible 
  cloud. 
  

  

  