﻿Ammonium 
  Magnesium 
  Arseniate 
  of 
  Analysis. 
  59 
  

  

  shows 
  a 
  tendency 
  here 
  to 
  form 
  a 
  salt 
  richer 
  in 
  ammonia 
  than 
  

   the 
  ideal 
  MgNH 
  4 
  As0 
  4 
  , 
  and 
  yielding 
  on 
  ignition 
  some 
  meta- 
  

   arseniate 
  instead 
  of 
  the 
  normal 
  pyroarseniate. 
  In 
  section 
  B 
  

   the 
  magnesium 
  ammonium 
  arseniate 
  was 
  precipitated 
  by 
  add- 
  

   ing 
  to 
  the 
  solution 
  of 
  arsenic 
  acid 
  magnesia 
  mixture 
  containing 
  

   no 
  free 
  ammonia 
  in 
  the 
  proportion 
  necessary 
  (50 
  em3 
  ) 
  to 
  remove 
  

   the 
  arsenic 
  from 
  solution, 
  and 
  then 
  making 
  the 
  solution 
  dis- 
  

   tinctly 
  ammoniacal. 
  After 
  the 
  precipitate 
  had 
  subsided, 
  it 
  was 
  

   filtered 
  off 
  on 
  asbestos 
  under 
  pressure 
  in 
  a 
  perforated 
  platinum 
  

   crucible, 
  washed 
  on 
  the 
  felt 
  with 
  ammoniacal 
  water, 
  dried 
  and 
  

   ignited. 
  These 
  results 
  are 
  also 
  below 
  the 
  theory 
  for 
  the 
  pyro- 
  

   arseniate. 
  Evidently 
  the 
  conditions 
  here 
  are 
  even 
  better 
  for 
  

   the 
  formation 
  of 
  the 
  salt 
  too 
  rich 
  in 
  ammonia 
  than 
  they 
  were 
  in 
  

   the 
  first 
  case. 
  ~No 
  arsenic 
  was 
  found 
  by 
  hydrogen 
  sulphide 
  in 
  

   any 
  case 
  either 
  in 
  the 
  filtrate 
  or 
  in 
  the 
  wash 
  water 
  after 
  acidify- 
  

  

  ing 
  and 
  heating. 
  

  

  

  TA3LE 
  III. 
  

  

  

  

  Mg 
  2 
  As 
  2 
  7 
  

  

  correspond] 
  

  

  ing 
  to 
  As 
  2 
  5 
  . 
  

  

  

  As 
  2 
  5 
  

  

  , 
  

  

  A 
  

  

  » 
  

  

  A 
  

  

  found 
  by 
  

  

  Taken. 
  

  

  Found. 
  

  

  Error. 
  

  

  

  H 
  2 
  Sin 
  

  

  grm. 
  

  

  grm. 
  

  

  grm. 
  

  

  

  the 
  filtrate. 
  

  

  0-7843 
  

  

  0-7800 
  

  

  0-0043 
  — 
  

  

  

  none 
  

  

  0-7843 
  

  

  0-7794 
  

  

  0-0049- 
  

  

  B 
  

  

  none 
  

  

  07843 
  

  

  0-7772 
  

  

  0-0071 
  — 
  

  

  none 
  

  

  0-7843 
  

  

  0-7769 
  

  

  0-0074 
  — 
  

  

  

  none 
  

  

  In 
  section 
  A 
  of 
  Table 
  IV 
  the 
  results 
  recorded 
  were 
  obtained 
  

   by 
  precipitating 
  definite 
  portions 
  of 
  arsenic 
  acid 
  drawn 
  from 
  

   a 
  burette 
  into 
  a 
  platinum 
  dish 
  with 
  the 
  distinctly 
  ammoniacal 
  

   magnesia 
  mixture 
  in 
  proper 
  proportion, 
  and 
  afterward 
  adding 
  

   a 
  little 
  more 
  ammonia, 
  filtering 
  oil 
  on 
  asbestos 
  under 
  pressure 
  

   in 
  a 
  perforated 
  platinum 
  crucible 
  as 
  soon 
  as 
  the 
  precipitate 
  

   subsided, 
  washing 
  off 
  on 
  the 
  felt 
  with 
  ammoniacal 
  water 
  any 
  

   of 
  the 
  reagents 
  left 
  on 
  the 
  precipitate 
  in 
  transferring 
  it 
  to 
  the 
  

   felt 
  by 
  using 
  the 
  filtrate, 
  drying 
  and 
  igniting. 
  No 
  arsenic 
  was 
  

   found 
  in 
  any 
  case 
  in 
  the 
  filtrate 
  or 
  in 
  the 
  washwater 
  by 
  hydro- 
  

   gen 
  sulphide. 
  The 
  conditions 
  of 
  precipitation 
  here 
  prove 
  to 
  

   be 
  such, 
  as 
  the 
  results 
  show, 
  that 
  the 
  salt 
  of 
  ideal 
  constitution 
  

   is 
  formed. 
  Comparing 
  these 
  results 
  with 
  those 
  of 
  Table 
  III, 
  it 
  

   seems 
  that 
  the 
  conditions 
  under 
  which 
  the 
  salt 
  of 
  ideal 
  compo- 
  

   sition 
  is 
  formed 
  are 
  such 
  that 
  at 
  the 
  moment 
  and 
  in 
  the 
  locality 
  

   of 
  precipitation 
  the 
  amount 
  of 
  magnesium 
  chloride 
  in 
  a 
  certain 
  

   volume 
  of 
  solution 
  must 
  be 
  large 
  in 
  proportion 
  to 
  the 
  amount 
  

   of 
  ammonia 
  present 
  as 
  the 
  chloride 
  and 
  the 
  hydroxide 
  ; 
  other- 
  

   wise 
  the 
  ammonium 
  of 
  the 
  ammonium 
  arseniate, 
  naturally 
  

   formed 
  first, 
  does 
  not 
  suffer 
  sufficient 
  displacement 
  by 
  mag- 
  

   nesium 
  to 
  produce 
  the 
  normal 
  ammonium 
  magnesium 
  arseniate. 
  

  

  