﻿58 
  Austin 
  — 
  Constitution 
  of 
  the 
  

  

  In 
  order 
  to 
  find 
  how 
  much 
  arsenic 
  is 
  dissolved 
  from 
  the 
  

   ammonium 
  magnesium 
  arseniate 
  once 
  precipitated 
  so 
  that 
  no 
  

   arsenic 
  is 
  left 
  in 
  solution, 
  experiments 
  were 
  made 
  in 
  which 
  the 
  

   arsenic 
  in 
  the 
  filtrate 
  was 
  weighed 
  after 
  precipitating 
  by 
  hydro- 
  

   gen 
  sulphide 
  in 
  hot 
  acid 
  solution, 
  filtering 
  off 
  on 
  asbestos 
  under 
  

   pressure, 
  washing 
  successively 
  with 
  water, 
  alcohol, 
  carbon 
  

   disulphide, 
  alcohol, 
  and 
  water, 
  and 
  drying 
  at 
  100° 
  C. 
  

  

  

  Table 
  

  

  II. 
  

  

  

  H 
  2 
  containing 
  l 
  cc 
  

  

  NH4OH 
  

  

  As 
  2 
  5 
  

  

  As 
  2 
  5 
  fom 
  

  

  NH4OE 
  in 
  200 
  cc 
  . 
  

  

  S. 
  G. 
  0-96. 
  

  

  digested. 
  

  

  as 
  As 
  2 
  S 
  3 
  

  

  grm. 
  

  

  cc. 
  

  

  grm. 
  

  

  grm. 
  

  

  _ 
  . 
  _ 
  

  

  100 
  

  

  0-5 
  

  

  0-0019 
  

  

  _ 
  _ 
  _ 
  

  

  100 
  

  

  0-5 
  

  

  0-0026 
  

  

  100 
  

  

  

  0-5 
  

  

  0-0003 
  

  

  100 
  

  

  

  0-5 
  

  

  0-0005 
  

  

  10 
  

  

  

  0-5 
  

  

  0-0002 
  

  

  10 
  

  

  

  0-5 
  

  

  0-0004 
  

  

  It 
  is 
  evident 
  from 
  these 
  qualitative 
  tests 
  that, 
  so 
  far 
  as 
  con- 
  

   cerns 
  the 
  amount 
  of 
  arsenic 
  dissolved 
  from 
  the 
  ammonium 
  

   magnesium 
  arseniate, 
  it 
  is 
  safe 
  to 
  use 
  a 
  faintly 
  ammoniacal 
  

   washwater 
  in 
  small 
  amounts 
  — 
  less 
  than 
  100 
  cc 
  — 
  to 
  remove 
  traces 
  

   of 
  reagents 
  from 
  the 
  residue 
  after 
  it 
  is 
  gathered 
  upon 
  the 
  

   asbestos 
  felt. 
  Usually 
  25-50 
  cc 
  of 
  washwater 
  were 
  used 
  in 
  rins- 
  

   ing 
  off 
  the 
  precipitate 
  in 
  the 
  experiments 
  about 
  to 
  be 
  given 
  

   below. 
  

  

  The 
  solution 
  of 
  arsenic 
  employed 
  in 
  this 
  work 
  was 
  prepared 
  

   by 
  dissolving 
  ten 
  grams 
  of 
  pure 
  arsenious 
  oxide, 
  carefully 
  

   resublimed, 
  in 
  a 
  platinum 
  dish 
  in 
  an 
  excess 
  of 
  pure 
  nitric 
  acid 
  

   and 
  evaporating 
  on 
  the 
  waterbath 
  to 
  dryness, 
  dissolving 
  the 
  

   arsenic 
  acid 
  produced 
  in 
  water 
  and 
  diluting 
  to 
  a 
  volume 
  of 
  one 
  

   liter 
  in 
  a 
  standard 
  flask. 
  

  

  Definite 
  portions 
  of 
  this 
  solution 
  were 
  drawn 
  from 
  a 
  burette 
  

   into 
  a 
  platinum 
  dish 
  and 
  precipitated 
  with 
  magnesia 
  mixture 
  

   prepared 
  as 
  described 
  in 
  the 
  proportion 
  shown 
  necessary 
  by 
  

   the 
  qualitative 
  tests 
  for 
  the 
  complete 
  removal 
  of 
  the 
  arsenic 
  

   from 
  solution, 
  and 
  the 
  solution 
  was 
  made 
  distinctly 
  ammoni- 
  

   acal. 
  The 
  precipitate, 
  dissolved 
  in 
  hydrochloric 
  acid 
  in 
  slight 
  

   excess, 
  was 
  brought 
  down 
  again 
  by 
  ammonia 
  in 
  distinct 
  excess. 
  

   After 
  standing 
  until 
  the 
  precipitate 
  had 
  completely 
  subsided, 
  

   the 
  precipitate 
  was 
  gathered 
  on 
  an 
  asbestos 
  felt 
  in 
  a 
  perforated 
  

   platinum 
  crucible, 
  making 
  use 
  of 
  the 
  filtrate 
  to 
  remove 
  the 
  

   last 
  portions 
  of 
  the 
  precipitate 
  to 
  the 
  felt, 
  before 
  washing 
  any 
  

   reagents 
  from 
  it 
  on 
  the 
  felt 
  with 
  faintly 
  ammoniacal 
  water. 
  

   After 
  carefully 
  drying, 
  the 
  residue 
  was 
  ignited 
  to 
  the 
  pyro- 
  

   arseniate. 
  The 
  results 
  shown 
  in 
  A 
  fall 
  so 
  far 
  below 
  the 
  theory 
  

   for 
  magnesium 
  arseniate 
  that 
  it 
  seems 
  evident 
  that 
  the 
  arseniate 
  

  

  