﻿PRODUCTS 
  OF 
  DECOMPOSITION 
  OF 
  COMENIC 
  ACID. 
  233 
  

  

  The 
  crystals 
  contain 
  further 
  six 
  atoms 
  of 
  water, 
  according 
  to 
  one 
  experiment, 
  

  

  ("16-794 
  grains 
  air-dry 
  substance 
  lost 
  at 
  240° 
  Fahr. 
  

   ( 
  3-709 
  ... 
  water, 
  

  

  which 
  gives 
  for 
  100 
  parts, 
  22*08 
  ; 
  the 
  number 
  22-53 
  is 
  that 
  required 
  by 
  the 
  formula 
  

  

  MgO, 
  HO, 
  C 
  12 
  H 
  2 
  8 
  , 
  2 
  HO 
  + 
  6 
  aq. 
  

  

  Neutral 
  Comenate 
  of 
  Magnesia. 
  — 
  When 
  an 
  alkaline 
  ammoniacal 
  solution 
  of 
  

   comenic 
  acid 
  is 
  added 
  to 
  a 
  solution 
  of 
  sulphate 
  of 
  magnesia, 
  a 
  salt 
  is 
  precipi- 
  

   tated, 
  especially 
  on 
  stirring 
  the 
  fluid, 
  in 
  the 
  form 
  of 
  hard 
  crystalline 
  grains, 
  

   adhering 
  very 
  much 
  to 
  the 
  sides 
  and 
  bottom 
  of 
  the 
  vessel. 
  Under 
  the 
  microscope, 
  

   those 
  grains 
  are 
  found 
  to 
  be 
  made 
  up 
  of 
  groups 
  of 
  short 
  prismatic 
  needles. 
  They 
  

   are 
  insoluble 
  in 
  boiling 
  water. 
  They 
  lose 
  their 
  water 
  of 
  crystallization 
  at 
  212°, 
  

   but 
  only 
  after 
  long 
  exposure 
  to 
  that 
  heat 
  ; 
  thus 
  dried 
  they 
  give 
  the 
  following 
  

   results 
  on 
  analysis 
  : 
  — 
  

  

  {5*680 
  grains 
  dried 
  at 
  212° 
  gave 
  

   7'305 
  ... 
  carbonic 
  acid, 
  and 
  

   1-387 
  ... 
  water. 
  

   ( 
  5*422 
  grains 
  dried 
  at 
  212° 
  gave 
  

   \ 
  3 
  • 
  1 
  1 
  5 
  ... 
  sulphate 
  of 
  magnesia. 
  

  

  Experiment. 
  Calculation. 
  

  

  Carbon, 
  . 
  . 
  35-07 
  34-89 
  C 
  18 
  72 
  

  

  Hydrogen, 
  . 
  253 
  242 
  H 
  5 
  5 
  

  

  Oxygen 
  . 
  . 
  ... 
  42-66 
  O 
  n 
  88 
  

  

  Magnesia, 
  . 
  19-53 
  20-03 
  2 
  MgO 
  41-34 
  

  

  100-00 
  100-00 
  206-34 
  

  

  from 
  which 
  it 
  appears 
  that 
  the 
  formula 
  expressing 
  the 
  composition 
  of 
  the 
  salt, 
  

   dried 
  at 
  212°, 
  is 
  

  

  2 
  MgO, 
  C 
  12 
  H 
  2 
  8 
  + 
  3 
  HO. 
  

  

  I 
  endeavoured, 
  by 
  employing 
  a 
  higher 
  temperature, 
  to 
  obtain 
  a 
  salt 
  corre- 
  

   sponding 
  with 
  the 
  neutral 
  salts 
  of 
  lime 
  and 
  baryta, 
  in 
  the 
  amount 
  of 
  water 
  

   retained 
  at 
  the 
  same 
  heat; 
  but 
  in 
  the 
  experiment 
  I 
  made, 
  the 
  substance 
  lost 
  

   weight 
  at 
  250° 
  gradually 
  through 
  a 
  space 
  of 
  four 
  days, 
  and 
  then 
  the 
  loss 
  between 
  

   each 
  weighing 
  was 
  very 
  small. 
  It 
  yielded 
  21 
  3 
  per 
  cent, 
  of 
  magnesia, 
  which 
  is 
  

   more 
  by 
  a 
  half 
  per 
  cent, 
  than 
  is 
  required 
  by 
  a 
  salt 
  of 
  the 
  constitution 
  sought 
  for. 
  

   The 
  neutral 
  comenate 
  of 
  magnesia, 
  precipitated 
  as 
  above 
  mentioned, 
  has 
  the 
  com- 
  

   position 
  expressed 
  by 
  the 
  formula 
  

  

  2 
  MgO, 
  C 
  12 
  H 
  2 
  8 
  , 
  3 
  HO 
  + 
  8 
  aq. 
  

  

  the 
  eight 
  atoms 
  aq. 
  being 
  lost 
  at 
  212°. 
  

  

  ( 
  15-103 
  grains 
  air-dry 
  substance 
  lost 
  at 
  212° 
  

   \ 
  4-003 
  ... 
  water. 
  

  

  This 
  experimental 
  number, 
  calculated 
  for 
  100 
  parts, 
  gives 
  26-50 
  ; 
  the 
  number 
  

   calculated 
  from 
  the 
  above 
  formula 
  is 
  25-86. 
  

  

  VOL. 
  XX. 
  PART 
  II. 
  3 
  R 
  

  

  