﻿226 
  MR 
  HENRY 
  HOW 
  ON 
  CERTAIN 
  SALTS 
  AND 
  

  

  fully 
  into 
  the 
  relations 
  between 
  it, 
  which 
  was 
  now 
  named 
  Comenic 
  Acid, 
  Meconic 
  

   Acid, 
  and 
  Pyromeconic 
  Acid, 
  the 
  product 
  of 
  dry 
  distillation 
  common 
  to 
  both 
  the 
  

   former 
  bodies. 
  The 
  subject 
  was 
  further 
  discussed 
  by 
  Dr 
  Stenhouse,* 
  in 
  a 
  paper, 
  

   to 
  some 
  of 
  the 
  details 
  of 
  which 
  I 
  shall 
  have 
  occasion 
  to 
  refer. 
  

  

  I 
  employed 
  for 
  the 
  preparation 
  of 
  comenic 
  acid 
  the 
  process 
  of 
  Robiquet 
  as 
  

   modified 
  by 
  Gregory, 
  which 
  consists 
  in 
  boiling 
  crude 
  meconate 
  of 
  lime 
  (or, 
  still 
  

   better, 
  the 
  acid 
  salt 
  obtained 
  by 
  once 
  treating 
  this 
  substance 
  with 
  boiling 
  water 
  and 
  

   hydrochloric 
  acid) 
  with 
  a 
  quantity 
  of 
  pretty 
  concentrated 
  hydrochloric 
  acid 
  suffi- 
  

   cient 
  to 
  dissolve 
  it. 
  For 
  the 
  purification 
  of 
  the 
  acid 
  which 
  is 
  deposited 
  in 
  the 
  

   form 
  of 
  very 
  dark-coloured 
  hard 
  crystalline 
  grains, 
  Stenhouse 
  recommends 
  solu- 
  

   tion 
  in 
  a 
  slight 
  excess 
  of 
  caustic 
  potass 
  or 
  soda, 
  and 
  recrystallization 
  of 
  the 
  salt 
  

   deposited 
  from 
  the 
  boiling 
  fluid. 
  I 
  preferred, 
  however, 
  to 
  use 
  ammonia, 
  since, 
  if 
  

   certain 
  precautions 
  are 
  adopted, 
  a 
  salt 
  is 
  obtained 
  as 
  readily 
  deprived 
  of 
  colour 
  as 
  

   the 
  potass 
  salt, 
  and 
  much 
  more 
  insoluble 
  in 
  cold 
  water 
  than 
  the 
  corresponding 
  

   salt 
  of 
  soda 
  ; 
  while 
  the 
  mother 
  liquors 
  afforded 
  a 
  convenient 
  means 
  of 
  trying 
  the 
  

   action 
  of 
  various 
  chemical 
  agents 
  upon 
  the 
  acid. 
  The 
  process 
  I 
  employed 
  consists 
  

   in 
  boiling 
  the 
  dark-coloured 
  grains 
  in 
  water, 
  with 
  gradual 
  addition 
  of 
  caustic 
  

   ammonia, 
  till 
  the 
  whole 
  is 
  in 
  solution. 
  The 
  fluid 
  is 
  then 
  immediately 
  filtered. 
  

   The 
  addition 
  of 
  an 
  excess 
  of 
  ammonia, 
  and 
  the 
  continuance 
  of 
  a 
  boiling 
  heat 
  are 
  

   to 
  be 
  avoided, 
  as 
  there 
  ensues, 
  if 
  this 
  be 
  not 
  attended 
  to, 
  a 
  curious 
  decomposition, 
  

   attended 
  with 
  the 
  production 
  of 
  much 
  colouring 
  matter, 
  the 
  explanation 
  of 
  which 
  

   will 
  be 
  entered 
  into 
  subsequently. 
  

  

  The 
  ammonia 
  salt 
  obtained 
  as 
  above, 
  deposits 
  from 
  the 
  black 
  fluid 
  in 
  yellow 
  

   hard 
  crystals 
  if 
  the 
  solution 
  is 
  left 
  at 
  rest, 
  but 
  in 
  soft 
  silky 
  prisms 
  when 
  it 
  is 
  agi- 
  

   tated 
  ; 
  in 
  the 
  latter 
  state 
  the 
  salt 
  is 
  not 
  so 
  readily 
  washed 
  free 
  of 
  the 
  coloured 
  

   mother 
  liquor. 
  By 
  two 
  or 
  three 
  crystallizations 
  from 
  boiling 
  water, 
  a 
  salt 
  of 
  

   dazzling 
  whiteness, 
  in 
  fine 
  radiated 
  four-sided 
  prisms, 
  is 
  obtained. 
  

  

  From 
  solutions 
  of 
  this 
  salt, 
  which, 
  when 
  even 
  quite 
  pure, 
  have 
  a 
  faint 
  shade 
  

   of 
  straw-colour, 
  the 
  addition 
  of 
  concentrated 
  hydrochloric 
  acid 
  throws 
  down 
  co- 
  

   menic 
  acid 
  in 
  the 
  form 
  of 
  a 
  white 
  heavy 
  crystalline 
  powder 
  adhering 
  to 
  the 
  sides 
  

   of 
  the 
  vessel, 
  which, 
  when 
  dissolved 
  in 
  boiling 
  water, 
  in 
  which 
  it 
  is 
  not 
  very 
  so- 
  

   luble, 
  is 
  deposited 
  from 
  a 
  saturated 
  solution 
  in 
  grains 
  and 
  crusts, 
  almost 
  colour- 
  

   less 
  ; 
  but 
  as 
  the 
  solution 
  cools, 
  groups 
  of 
  short 
  prismatic, 
  or 
  sometimes 
  leaf-like, 
  

   crystals 
  appear, 
  always 
  possessing 
  a 
  characteristic 
  yellowish-red 
  tinge 
  of 
  colour. 
  

  

  The 
  general 
  chemical 
  and 
  physical 
  properties 
  of 
  comenic 
  acid 
  have 
  been 
  already 
  

   too 
  well 
  described 
  to 
  require 
  any 
  special 
  remarks 
  on 
  my 
  part 
  ; 
  I 
  shall 
  therefore 
  

   proceed 
  at 
  once 
  to 
  the 
  details 
  of 
  the 
  salts 
  I 
  have 
  examined. 
  

  

  Bicomenate 
  of 
  Ammonia. 
  

   This 
  salt 
  was 
  obtained 
  and 
  analysed 
  by 
  Stenhouse, 
  who 
  formed 
  it 
  by 
  solution 
  

  

  * 
  Mem. 
  and 
  Proc. 
  Chem. 
  Soc, 
  vol. 
  i. 
  

  

  