﻿58 
  Druskel 
  and 
  Felty 
  — 
  Preparation, 
  etc., 
  of 
  

  

  with 
  standard 
  sodium 
  hydroxide. 
  The 
  dipropylphosphoric 
  

   acid 
  was 
  also 
  prepared 
  from 
  the 
  sodium 
  salt 
  by 
  adding 
  the 
  

   theoretical 
  amount 
  of 
  sulphuric 
  acid, 
  evaporating 
  the 
  solution 
  

   on 
  the 
  steam 
  bath 
  and 
  extracting 
  the 
  free 
  acid 
  from 
  the 
  residue 
  

   with 
  absolute 
  alcohol, 
  the 
  alcoholic 
  solution 
  was 
  diluted 
  with 
  

   water, 
  concentrated 
  in 
  platinum 
  on 
  the 
  steam 
  bath 
  and 
  finally 
  

   made 
  up 
  to 
  the 
  proper 
  normality 
  with 
  distilled 
  water. 
  The 
  

   solution 
  was 
  found 
  to 
  be 
  free 
  from 
  sulphate 
  and 
  its 
  normality 
  

   was 
  checked 
  up 
  by 
  making 
  a 
  titration 
  with 
  standard 
  sodium 
  

   hydroxide 
  solution. 
  

  

  (h) 
  The 
  isomeric 
  benzenedisul 
  phonic 
  acids 
  and 
  their 
  alkali 
  

   salts. 
  For 
  the 
  preparation 
  of 
  these 
  acids 
  and 
  their 
  potassium 
  

   salts 
  methods 
  were 
  chosen 
  which 
  give 
  each 
  acid 
  and 
  its 
  salt 
  

   entirely 
  free 
  from 
  the 
  acid 
  or 
  salt 
  of 
  either 
  of 
  its 
  two 
  isomers. 
  

   This 
  is 
  important 
  in 
  the 
  present 
  investigation, 
  for 
  in 
  order 
  to 
  

   compare 
  the 
  strengths 
  of 
  the 
  three 
  isomeric 
  benzenedisulphonic 
  

   acids 
  it 
  is 
  necessary 
  that 
  each 
  acid 
  should 
  be 
  prepared 
  entirely 
  

   free 
  from 
  its 
  two 
  isomers. 
  The 
  m-benzenedisulphonic 
  acid 
  is 
  

   the 
  only 
  one 
  of 
  the 
  acids 
  prepared 
  by 
  the 
  direct 
  sulphonation 
  

   of 
  benzene. 
  When 
  benzene 
  is 
  sulphonated 
  benzenemono- 
  

   sul 
  phonic, 
  m-benzenedisulphonic, 
  s-benzenetrisulphonic, 
  and 
  

   possibly 
  under 
  special 
  conditions, 
  a 
  little 
  ^-benzenedisulphonic 
  

   acid 
  may 
  be 
  formed 
  ; 
  but 
  by 
  properly 
  regulating 
  the 
  tempera- 
  

   ture 
  and 
  concentration 
  of 
  the 
  sulphuric 
  acid 
  the 
  only 
  products 
  

   are 
  the 
  monosulphonic 
  acid, 
  the 
  wi-disulphonic 
  acid, 
  a 
  little 
  

   excess 
  of 
  sulphuric 
  acid 
  and 
  a 
  trace 
  of 
  benzene. 
  The 
  benzene 
  

   was 
  removed 
  by 
  water, 
  the 
  excess 
  of 
  sulphuric 
  acid 
  as 
  barium 
  

   sulphate, 
  and 
  the 
  strongly 
  acid 
  aqueous 
  filtrate 
  was 
  then 
  con- 
  

   verted 
  to 
  the 
  potassium 
  salt 
  by 
  exact 
  neutralization 
  with 
  

   potassium 
  hydroxide 
  or 
  carbonate, 
  and 
  evaporation 
  to 
  crystal- 
  

   lization. 
  By 
  a 
  number 
  of 
  recrystallizations 
  the 
  pure 
  potassium 
  

   m-benzenedisulphonate 
  was 
  obtained 
  in 
  good 
  yield, 
  the 
  mono- 
  

   sulphonate 
  tending 
  always 
  to 
  remain 
  in 
  the 
  mother 
  liquor. 
  

   Potassium 
  ?7?-benzenedisulphonate 
  was 
  readily 
  converted 
  into 
  

   the 
  pure 
  acid 
  by 
  the 
  following 
  procedure. 
  The 
  potassium 
  

   salt 
  was 
  dried 
  at. 
  200°-220° 
  to 
  remove 
  the 
  molecule 
  of 
  water 
  

   of 
  crystallization 
  and 
  the 
  anhydrous 
  salt 
  was 
  then 
  mixed 
  with 
  

   the 
  theoretical 
  amount 
  of 
  powdered 
  phosphorus 
  pentachloride 
  

   and 
  warmed. 
  After 
  the 
  reaction 
  was 
  over 
  the 
  mixture 
  was 
  

   treated 
  with 
  cold 
  water 
  to 
  remove 
  the 
  sodium 
  chloride 
  formed 
  

   in 
  the 
  reaction, 
  the 
  insoluble 
  diacid 
  chloride 
  was 
  filtered 
  off, 
  

   dried 
  and 
  purified 
  by 
  recrystallization 
  from 
  ether. 
  The 
  diacid 
  

   chloride 
  was 
  obtained 
  in 
  quantitative 
  yield 
  and 
  was 
  converted 
  

   to 
  the 
  acid 
  by 
  heating 
  for 
  an 
  hour 
  with 
  distilled 
  water. 
  This 
  

   acid 
  solution 
  was 
  then 
  treated 
  with 
  a 
  little 
  more 
  than 
  the 
  

   theoretical 
  amount 
  of 
  pure 
  silver 
  oxide 
  necessary 
  to 
  remove 
  the 
  

   hydrochloric 
  acid 
  formed 
  in 
  the 
  hydrolysis. 
  Care 
  was 
  exercised 
  

  

  