﻿and 
  Chemical 
  Reactions 
  in 
  Heterogeneous 
  Systems. 
  543 
  

  

  thousand 
  atmospheres. 
  The 
  substance 
  is 
  brought 
  into 
  a 
  steel 
  

   ring 
  of 
  an 
  internal 
  diameter 
  = 
  51 
  mm., 
  external 
  diameter 
  

   = 
  127 
  mm., 
  placed 
  in 
  the 
  steel 
  base 
  (PI. 
  XYIII.), 
  and 
  is 
  com- 
  

   pressed 
  here 
  under 
  several 
  thousand 
  atmospheres 
  with 
  the 
  

   piston, 
  which 
  is 
  51 
  mm. 
  diameter 
  and 
  12 
  cm. 
  long. 
  The 
  dia- 
  

   meter 
  o£ 
  the 
  piston 
  is 
  51 
  mm., 
  or 
  very 
  nearly 
  2 
  inches. 
  The 
  

   diameter 
  of 
  the 
  ram 
  of 
  the 
  hydraulic 
  press 
  is 
  10 
  inches, 
  the 
  

   ram 
  is 
  compressed 
  to 
  75 
  or 
  100 
  atmospheres 
  on 
  the 
  gauge, 
  

   thus 
  producing 
  a 
  pressure 
  on 
  the 
  piston 
  and 
  the 
  substance 
  of 
  

   75x25 
  = 
  1875, 
  or 
  100x25 
  = 
  2500 
  atmospheres 
  per 
  square 
  

   inch. 
  The 
  maximum 
  compression 
  of 
  the 
  solid 
  usually 
  takes 
  

   place 
  much 
  below 
  these 
  pressures, 
  already 
  at 
  about 
  1000 
  to 
  

   1400 
  atmospheres, 
  and 
  often 
  below 
  this. 
  The 
  substances 
  are 
  

   left 
  under 
  the 
  above 
  pressure 
  usually 
  for 
  16 
  to 
  24 
  hours, 
  

   when 
  the 
  pressure 
  is 
  generally 
  released 
  ; 
  the 
  base 
  is 
  then 
  

   removed 
  from 
  the 
  ring 
  containing 
  the 
  compressed 
  block 
  of 
  

   the 
  substance, 
  and 
  the 
  latter 
  is 
  pushed 
  out 
  from 
  the 
  ring 
  

   (the 
  pressure 
  usually 
  required 
  is 
  70 
  to 
  350 
  atmospheres 
  per 
  

   square 
  inch), 
  with 
  the 
  piston, 
  into 
  a 
  steel 
  ring 
  of 
  a 
  larger 
  

   diameter 
  placed 
  below 
  the 
  ring, 
  it 
  being 
  arranged 
  that 
  the 
  

   disk 
  should 
  fall 
  on 
  a 
  piece 
  of 
  soft 
  felt 
  below. 
  The 
  ring, 
  

   base, 
  and 
  piston 
  must 
  be 
  perfectly 
  polished 
  so 
  as 
  to 
  get 
  a 
  

   perfect 
  uninjured 
  block. 
  The 
  ring 
  itself 
  was 
  a 
  little 
  modified, 
  

   made 
  internally 
  a 
  little 
  conical 
  (a 
  fraction 
  of 
  a 
  mm. 
  suffices) 
  

   from 
  top 
  to 
  bottom, 
  in 
  order 
  that 
  the 
  block 
  of 
  substance 
  

   shall 
  leave 
  the 
  ring 
  at 
  once, 
  as 
  soon 
  as 
  it 
  is 
  moved 
  by 
  the 
  

   piston, 
  instead 
  of 
  its 
  requiring 
  to 
  be 
  pressed 
  through 
  the 
  

   ring 
  through 
  its 
  whole 
  thickness. 
  In 
  such 
  a 
  way 
  we 
  get 
  

   beautiful 
  disks, 
  with 
  perfect 
  surfaces, 
  free 
  from 
  any 
  

   air-holes, 
  cracks, 
  &c., 
  requiring 
  no 
  admixtures 
  in 
  order 
  

   to 
  make 
  the 
  substance 
  stick 
  well 
  together, 
  with 
  perfect 
  

   uniformity 
  through 
  their 
  whole 
  thickness 
  ; 
  whether 
  the 
  sub- 
  

   stance 
  is 
  crystalline 
  or 
  amorphous, 
  an 
  organic 
  or 
  inorganic 
  

   solid, 
  a 
  compound 
  or 
  an 
  element 
  (S, 
  C, 
  metal 
  powders, 
  &c.), 
  

   it 
  is 
  crushed 
  to 
  a 
  uniform 
  body 
  ; 
  one 
  disk 
  1*5 
  to 
  2 
  cm. 
  

   thick 
  is 
  quite 
  enough 
  for 
  carrying 
  out 
  a 
  long 
  series 
  of 
  com- 
  

   parative 
  experiments, 
  and 
  we 
  are 
  able 
  to 
  i^olish 
  and 
  to 
  rectify 
  

   over 
  and 
  over 
  again 
  the 
  surface 
  of 
  the 
  same 
  block 
  for 
  the 
  same 
  

   experiment, 
  because 
  it 
  must 
  be 
  a 
  strict 
  rule 
  to 
  allow 
  the 
  

   solid 
  to 
  corrode 
  during 
  solution 
  only 
  as 
  little 
  as 
  possible 
  and 
  

   to 
  repolish 
  the 
  same 
  as 
  often 
  as 
  is 
  practicable. 
  We 
  can 
  

   keep 
  the 
  dissolving 
  surface 
  of 
  the 
  solid 
  always 
  at 
  nearly 
  

   the 
  same 
  height 
  in 
  the 
  liquid, 
  by 
  fixing 
  the 
  blocks 
  to 
  

   ebonite 
  disks 
  of 
  different 
  thicknesses. 
  Photo 
  10 
  (PL 
  XVII.) 
  

   shows 
  a 
  disk 
  of 
  benzoic 
  acid 
  before 
  treatment 
  ; 
  photo 
  10 
  A 
  

   shows 
  the 
  block 
  of 
  benzoic 
  acid 
  after 
  solution 
  in 
  water 
  

  

  