﻿316 
  M. 
  C. 
  Lea 
  — 
  Allotropic 
  Silver. 
  

  

  dextrine 
  and 
  fixed 
  alkaline 
  hydroxide 
  ; 
  (3) 
  acting 
  on 
  silver 
  

   nitrate 
  or 
  carbonate 
  by 
  tannin 
  and 
  fixed 
  alkaline 
  carbonate. 
  

   Now, 
  if 
  in 
  either 
  of 
  these 
  three 
  cases 
  we 
  interrupt 
  the 
  action 
  

   before 
  it 
  is 
  complete 
  by 
  adding 
  an 
  excess 
  of 
  dilute 
  hydro- 
  

   chloric 
  acid 
  we 
  shall 
  obtain 
  a 
  dark 
  chestnut-brown 
  or 
  some- 
  

   times 
  purple-brown 
  substance 
  which 
  on 
  examination 
  proves 
  to 
  

   be 
  a 
  mixture 
  of 
  silver 
  subchloride 
  and 
  photochloride. 
  When, 
  

   after 
  complete 
  removal 
  of 
  the 
  excess 
  of 
  hydrochloric 
  acid 
  by 
  

   thorough 
  washing 
  or 
  better 
  by 
  boiling 
  with 
  distilled 
  water, 
  the 
  

   substance 
  is 
  treated 
  with 
  cold 
  dilute 
  nitric 
  acid 
  that 
  portion 
  of 
  

   the 
  sub-chloride 
  which 
  is 
  not 
  combined 
  with 
  the 
  normal 
  

   chloride 
  is 
  broken 
  up 
  and 
  there 
  remains 
  photochloride 
  of 
  a 
  

   very 
  rich 
  and 
  intense 
  rose-color.* 
  

  

  The 
  production 
  of 
  silver 
  sub-chloride 
  in 
  all 
  these 
  cases 
  

   would 
  seem 
  to 
  indicate 
  that 
  the 
  reduction 
  when 
  the 
  acid 
  was 
  

   added 
  was 
  incomplete, 
  and 
  that 
  in 
  case 
  (1) 
  a 
  sub-salt, 
  and 
  in 
  

   cases 
  (2) 
  and 
  (3) 
  a 
  sub-oxide 
  was 
  first 
  formed 
  as 
  an 
  intermediate 
  

   step 
  before 
  complete 
  reduction. 
  Either 
  of 
  these 
  substances 
  

   would 
  of 
  course 
  give 
  rise 
  to 
  the 
  formation 
  of 
  subchloride 
  

   when 
  treated 
  with 
  hydrochloric 
  acid. 
  It 
  is 
  important 
  to 
  ob- 
  

   serve 
  that 
  this 
  result 
  is 
  to 
  be 
  obtained 
  only 
  by 
  interrupting 
  the 
  

   reaction 
  before 
  it 
  is 
  complete. 
  When, 
  for 
  example, 
  allotropic 
  

   silver 
  in 
  solution 
  is 
  produced 
  by 
  the 
  action 
  of 
  sodic 
  hydroxide 
  

   and 
  dextrine 
  and 
  after 
  complete 
  reduction, 
  hydrochloric 
  acid 
  is 
  

   added, 
  the 
  liquid 
  becomes 
  filled 
  with 
  gray 
  normal 
  silver, 
  which 
  

   presently 
  collects 
  to 
  a 
  cake. 
  When 
  this 
  cake 
  is 
  well 
  washed 
  

   and 
  boiled 
  with 
  water, 
  and 
  then 
  treated 
  with 
  dilute 
  nitric 
  acid, 
  

   solution 
  takes 
  place 
  : 
  a 
  trace 
  of 
  photochloride 
  is 
  left 
  behind. 
  

   It 
  has 
  been 
  mentioned 
  elsewhere 
  that 
  hydrochloric 
  acid, 
  

   though 
  without 
  action 
  on 
  ordinary 
  silver, 
  is 
  capable 
  of 
  form- 
  

   ing 
  a 
  variable 
  quantity 
  of 
  protochloride 
  when 
  placed 
  in 
  contact 
  

   with 
  allotropic 
  silver. 
  

  

  I 
  have 
  not 
  met 
  with 
  any 
  exception 
  to 
  this 
  general 
  principle 
  

   that 
  when 
  a 
  reaction 
  leading 
  to 
  the 
  formation 
  of 
  allotropic 
  

   silver 
  is 
  interrupted 
  by 
  the 
  addition 
  of 
  hydrochloric 
  acid, 
  

   subchloride 
  is 
  abundantly 
  formed 
  as 
  one 
  of 
  the 
  products. 
  

  

  In 
  all 
  such 
  cases 
  the 
  reduction 
  is 
  evidently 
  indirect. 
  The 
  

   silver 
  does 
  not 
  lose 
  at 
  once 
  the 
  whole 
  of 
  its 
  oxygeu, 
  but 
  

   apparently 
  passes 
  through 
  an 
  intermediate 
  form, 
  probably 
  

   Ag 
  4 
  0, 
  the 
  reduction 
  of 
  which 
  tends 
  to 
  the 
  formation 
  of 
  allo- 
  

   tropic 
  silver. 
  

  

  These 
  facts 
  lead 
  directly 
  up 
  to 
  the 
  question 
  : 
  does 
  silver 
  

   exist 
  in 
  its 
  subsalts 
  in 
  the 
  allotropic 
  form 
  ? 
  There 
  are 
  some 
  

  

  * 
  This 
  is 
  a 
  very 
  beautiful 
  reaction 
  and 
  deserves 
  more 
  particular 
  mention 
  than 
  

   can 
  be 
  given 
  here. 
  It 
  is 
  perhaps 
  the 
  best 
  means 
  for 
  obtaining 
  silver 
  photochlo- 
  

   ride, 
  for 
  which 
  purpose 
  I 
  have 
  often 
  employed 
  it, 
  both 
  on 
  account 
  of 
  its 
  facility 
  

   and 
  certainty, 
  and 
  the 
  very 
  beautiful 
  color 
  of 
  the 
  product. 
  

  

  