﻿CRYSTALLINE 
  STRUCTURE 
  BY 
  COMPRESSION 
  AND 
  TRACTION. 
  

  

  557 
  

  

  Strychnine, 
  sulphate 
  of. 
  

  

  acetate 
  of. 
  

   Soda, 
  native 
  nitrate 
  of. 
  

   Berberine. 
  

   Mucic 
  acid. 
  

   Solanine. 
  

   Asparagine. 
  

  

  Mercury, 
  oxymuriate 
  of. 
  

  

  Isatine. 
  

  

  Alizarine. 
  

  

  Manganese, 
  sesquioxide 
  of. 
  

  

  Lead, 
  protoxide 
  of. 
  

  

  Tungstic 
  acid. 
  

  

  Chromo-oxalate 
  of 
  potash. 
  

  

  In 
  submitting 
  other 
  crystals 
  to 
  the 
  influence 
  of 
  compression 
  and 
  traction, 
  I 
  

   have 
  found 
  great 
  numbers 
  which 
  do 
  not 
  exhibit 
  the 
  least 
  trace 
  of 
  transparent 
  

   streaks 
  and 
  lines, 
  the 
  separate 
  particles 
  being 
  merely 
  dragged 
  into 
  lines, 
  and 
  ex- 
  

   hibiting 
  only 
  a 
  quaquaversus 
  polarisation. 
  On 
  the 
  other 
  hand, 
  there 
  is 
  another 
  

   class 
  of 
  crystals, 
  whose 
  powders 
  or 
  particles 
  are 
  forced 
  into 
  distinct 
  and 
  transpa- 
  

   rent 
  streaks 
  and 
  lines 
  in 
  which 
  the 
  individual 
  particles 
  have 
  a 
  quaquaversus 
  

   polarisation, 
  and 
  no 
  trace 
  of 
  a 
  prismatic 
  arrangement. 
  As 
  these 
  crystals 
  have 
  a 
  

   peculiar 
  relation 
  to 
  those 
  in 
  the 
  preceding 
  list, 
  I 
  shall 
  enumerate 
  the 
  most 
  im- 
  

   portant 
  of 
  them 
  in 
  the 
  following 
  table 
  ; 
  that 
  is, 
  those 
  in 
  which 
  the 
  powder 
  has 
  

   been 
  dragged 
  into 
  transparent 
  and 
  continuous 
  streaks 
  and 
  lines, 
  resembling 
  exter- 
  

   nally 
  portions 
  of 
  a 
  solid 
  body 
  ; 
  for 
  it 
  is 
  only 
  by 
  a 
  comparison 
  of 
  the 
  physical, 
  or 
  

   perhaps 
  the 
  chemical 
  qualities 
  of 
  the 
  two 
  classes 
  of 
  bodies, 
  that 
  we 
  can 
  expect 
  to 
  

   explain 
  the 
  new 
  property 
  which 
  is 
  possessed 
  only 
  by 
  one 
  of 
  them. 
  

  

  Hydrate 
  of 
  potash, 
  pure. 
  

  

  Indigotic 
  acid. 
  

  

  Urea. 
  

  

  Citric 
  acid. 
  

  

  Silver, 
  nitrate 
  of. 
  

  

  Meconine. 
  

  

  Napthaline. 
  

  

  Soda, 
  nitrate 
  of. 
  

  

  Potash 
  and 
  copper, 
  sulphate 
  of. 
  

  

  Soda, 
  phosphate 
  of. 
  

  

  Soda, 
  acetate 
  of. 
  

   Mercury, 
  prussiate 
  of. 
  

  

  muriate 
  of. 
  

  

  sulphuret 
  of. 
  

   Barytes, 
  acetate 
  of. 
  

   Zinc, 
  chromate 
  of. 
  

   ... 
  sulphate 
  of. 
  

   Cobalt, 
  sulphate 
  of. 
  

   Magnesia 
  and 
  soda, 
  sulphate 
  of. 
  

   Borax. 
  

  

  As 
  both 
  compression 
  and 
  traction 
  are 
  necessary 
  in 
  producing 
  the 
  transparent 
  

   streaks 
  and 
  lines 
  in 
  both 
  classes 
  of 
  the 
  substances 
  I 
  have 
  enumerated, 
  it 
  became 
  

   interesting 
  to 
  ascertain 
  what 
  effect 
  was 
  produced 
  by 
  each 
  of 
  these 
  forces 
  acting 
  

   separately, 
  and 
  which 
  of 
  them 
  was 
  chiefly 
  influential 
  in 
  developing 
  the 
  doubly 
  

   refracting 
  arrangement 
  exhibited 
  by 
  the 
  substances 
  that 
  possessed 
  it. 
  

  

  The 
  force 
  of 
  compression 
  was 
  undoubtedly 
  the 
  agent 
  in 
  forcing 
  the 
  separate 
  

   particles 
  into 
  optical 
  contact, 
  while 
  that 
  of 
  traction 
  drew 
  them 
  into 
  a 
  line, 
  and 
  

   tended 
  to 
  dilate 
  the 
  film 
  in 
  the 
  direction 
  of 
  that 
  line, 
  and 
  to 
  draw 
  its 
  particles 
  

   from 
  each 
  other 
  ; 
  or 
  overcome 
  their 
  attraction 
  of 
  aggregation 
  in 
  that 
  direction. 
  It 
  

   is 
  quite 
  possible, 
  too, 
  that 
  these 
  forces 
  may 
  have 
  exercised 
  some 
  influence 
  in 
  

   modifying 
  the 
  doubly 
  refracting 
  structure 
  of 
  the 
  substance 
  under 
  examination 
  ; 
  

   but 
  as 
  such 
  a 
  question 
  has 
  no 
  bearing 
  upon 
  our 
  present 
  subject, 
  I 
  have 
  not 
  at- 
  

   tempted 
  its 
  solution. 
  

  

  