﻿

  Some 
  Properties 
  of 
  Artists' 
  Colours. 
  125 
  

  

  be 
  used 
  without 
  a 
  large 
  factor 
  of 
  safety. 
  The 
  maximum 
  

   shear 
  theory 
  agrees 
  very 
  nearly 
  with 
  the 
  results 
  of 
  tests 
  

   and 
  the 
  resulting 
  formula, 
  or 
  some 
  slight 
  modification 
  of 
  

   it 
  should 
  be 
  used 
  in 
  practice. 
  The 
  following 
  formula} 
  are 
  

  

  recommended 
  :- 
  

  

  V- 
  

  

  *■%*& 
  

  

  m, 
  2 
  = 
  m! 
  + 
  (^ 
  2 
  )m?. 
  

  

  LXII. 
  Some 
  Properties 
  of 
  Artists 
  3 
  Colours. 
  

   By 
  Herbert 
  Edmeston 
  Watson, 
  B.Sc, 
  A.LC* 
  

  

  Part 
  I. 
  — 
  The 
  Stability 
  of 
  Paints, 
  

  

  THIS 
  subject 
  is 
  by 
  no 
  means 
  a 
  new 
  one, 
  having 
  pro- 
  

   bably 
  occupied 
  the 
  attention 
  of 
  colour 
  manufacturers 
  

   from 
  the 
  earliest 
  times, 
  while 
  in 
  1888 
  a 
  report 
  on 
  "The 
  Action 
  

   of 
  Light 
  on 
  Water 
  Colours 
  " 
  was 
  made 
  to 
  the 
  Government. 
  

   Up 
  till 
  now, 
  however, 
  not 
  much 
  work 
  seems 
  to 
  have 
  been 
  

   done 
  in 
  investigating 
  the 
  precise 
  change 
  which 
  paints 
  undergo 
  

   when 
  they 
  fade. 
  

  

  The 
  chemical 
  reaction 
  which 
  takes 
  place 
  is 
  probably 
  of 
  

   quite 
  a 
  simple 
  nature, 
  and 
  if 
  it 
  is 
  the 
  same 
  for 
  the 
  majority 
  

   of 
  paints, 
  it 
  should 
  not 
  be 
  hard 
  to 
  discover. 
  Bearing 
  this 
  

   fact 
  in 
  mind, 
  the 
  action 
  of 
  hydrogen 
  peroxide 
  on 
  paints 
  was 
  

   tried, 
  for 
  this 
  substance 
  is 
  known 
  to 
  be 
  formed 
  by 
  the 
  action 
  

   of 
  air 
  on 
  water 
  in 
  presence 
  of 
  organic 
  matter 
  and 
  light, 
  and 
  

   moreover 
  it 
  is 
  a 
  very 
  active 
  reagent. 
  The 
  experimental 
  

   part 
  was 
  carried 
  out 
  as 
  follows 
  : 
  — 
  

  

  A 
  small 
  portion 
  of 
  the 
  pure 
  finely-ground 
  paint 
  to 
  be 
  

   investigated 
  was 
  well 
  stirred 
  up 
  with 
  water, 
  and 
  a 
  few 
  drops 
  

   of 
  the 
  suspension 
  poured 
  into 
  each 
  of 
  two 
  small 
  test-tubes. 
  

   In 
  this 
  way, 
  very 
  minute, 
  but 
  approximately 
  equal 
  quantities 
  

   were 
  obtained. 
  To 
  one 
  test-tube 
  was 
  added 
  about 
  1 
  c.c^ 
  of 
  

   the 
  purest 
  hydrogen 
  peroxide 
  solution 
  (10 
  vols.), 
  and 
  to 
  the 
  

   other 
  an 
  equal 
  quantity 
  of 
  water. 
  Both 
  tubes 
  were 
  drawn 
  

   on 
  in 
  fine 
  capillaries, 
  to 
  avoid 
  loss 
  by 
  evaporation, 
  and 
  kept 
  

   side 
  by 
  side 
  for 
  a 
  fortnight 
  in 
  the 
  cold 
  ; 
  they 
  were 
  then 
  

   placed 
  in 
  a 
  steam 
  oven, 
  the 
  usual 
  temperature 
  of 
  which 
  was 
  

   about 
  40°, 
  for 
  a 
  year. 
  Observations 
  were 
  made 
  at 
  frequent 
  

   intervals, 
  and 
  by 
  comparing 
  the 
  two 
  tubes, 
  any 
  change 
  could 
  

  

  * 
  Communicated 
  by 
  Sir 
  William 
  Ramsay, 
  F.R.S. 
  

  

  