﻿and 
  Chemical 
  Reactions 
  in 
  Heterogeneous 
  Systems. 
  571 
  

  

  Italy, 
  Alabaster 
  from 
  Leicester, 
  fibrous 
  Gypsum 
  from 
  

   Nottingham, 
  all 
  perfect 
  specimens, 
  perfectly 
  polished 
  and 
  

   Avashed 
  and 
  dried 
  up 
  well 
  and 
  quickly; 
  their 
  surface 
  is 
  almost 
  

   the 
  same, 
  about 
  4 
  sq. 
  in., 
  all 
  were 
  investigated 
  at 
  the 
  same 
  

   temperature 
  of 
  very 
  near 
  17°*5 
  C, 
  with 
  the 
  same 
  speed 
  of 
  

   stirrer 
  (130 
  to 
  132 
  revolutions 
  per 
  minute) 
  and 
  the 
  same 
  

   volume 
  (1500 
  cc.) 
  which 
  remained 
  constant 
  during 
  the 
  whole 
  

   time 
  of 
  the 
  reaction. 
  The 
  surface 
  of 
  the 
  selenite 
  exposed 
  

   to 
  solution 
  was 
  the 
  flat 
  large 
  side 
  of 
  the 
  twin-crystal, 
  the 
  

   surface 
  of 
  the 
  fibrous 
  gypsum 
  was 
  cut 
  along 
  the 
  fibre, 
  quite 
  

   parallel 
  to 
  the 
  same, 
  while 
  the 
  surface 
  of 
  alabaster 
  could 
  be 
  

   taken 
  in 
  any 
  direction. 
  Photos 
  11, 
  12, 
  13 
  (PL 
  XVII.) 
  show 
  

   Selenite, 
  Alabaster, 
  fibrous 
  Gypsum, 
  their 
  structure 
  and 
  their 
  

   surfaces 
  after 
  solution. 
  It 
  will 
  be 
  seen 
  from 
  the 
  same 
  that 
  

   their 
  surfaces 
  were 
  not 
  allowed 
  to 
  corrode. 
  The 
  selenite 
  is 
  

   transparent 
  like 
  glass, 
  and 
  what 
  we 
  see 
  on 
  the 
  photo 
  is 
  the 
  

   paraffin 
  below 
  the 
  bottom 
  surface. 
  On 
  the 
  contrary, 
  in 
  case 
  

   of 
  alabaster 
  and 
  fibrous 
  gypsum, 
  the 
  photos 
  show 
  their 
  

   structure, 
  not 
  corrosions, 
  which 
  are 
  extremely 
  small. 
  The 
  

   velocity 
  constant 
  of 
  Selenite 
  is 
  from 
  '48 
  to 
  about 
  '65, 
  of 
  the 
  

   fibrous 
  Gypsum 
  is 
  about 
  2*0, 
  of 
  the 
  Alabaster 
  from 
  3*1 
  to 
  

   about 
  4*0, 
  the 
  average 
  ratio 
  of 
  the 
  constants 
  of 
  Selenite 
  : 
  

   fibrous 
  Gypsum 
  : 
  Alabaster 
  at 
  the 
  same 
  surface 
  is 
  about 
  

   1 
  : 
  3*5 
  : 
  5'4. 
  Thus 
  Marienglass 
  and 
  Alabaster 
  give, 
  not 
  as 
  

   Bruner 
  and 
  Tolloczko 
  lead 
  us 
  to 
  think 
  almost 
  equal 
  constants, 
  

   but 
  very 
  different 
  constants 
  indeed, 
  and 
  all 
  the 
  three 
  above 
  

   specimens 
  of 
  the 
  same 
  Gypsum 
  give 
  undoubtedly 
  different 
  

   constants, 
  whether 
  we 
  take 
  extremely 
  dilute 
  solutions 
  given 
  

   by 
  the 
  first 
  three 
  dilutions 
  in 
  the 
  above 
  tables, 
  where 
  the 
  ratio 
  

   is 
  1:4:6, 
  or 
  the 
  more 
  concentrated 
  ones. 
  Therefore, 
  as 
  

   the 
  solubility 
  of 
  all 
  modifications 
  is 
  the 
  same, 
  it 
  is 
  sufficient 
  

   that 
  the 
  same 
  monoclinic 
  crystal 
  should 
  configurate 
  itself 
  

   once 
  into 
  a 
  twin-crystal, 
  another 
  time 
  into 
  a 
  fibrous 
  struc- 
  

   ture, 
  another 
  time 
  into 
  a 
  granular 
  crystalline 
  form 
  ; 
  and 
  

   this 
  physical 
  modification 
  in 
  the 
  configuration 
  of 
  the 
  very 
  

   same 
  components 
  is 
  already 
  alone 
  sufficient 
  to 
  cause 
  the 
  

   solid 
  to 
  acquire 
  some 
  new 
  physical 
  properties, 
  of 
  which 
  

   the 
  speed 
  of 
  solution 
  is 
  one. 
  All 
  the 
  above 
  three 
  spe- 
  

   cimens 
  are 
  as 
  we 
  find 
  them 
  in 
  nature, 
  their 
  velocity 
  con- 
  

   stants 
  undoubtedly 
  increase 
  as 
  the 
  reaction 
  goes 
  on, 
  and 
  

   this 
  may 
  be 
  due 
  either 
  to 
  corrosion 
  or 
  also 
  to 
  some 
  other 
  

   influences. 
  It 
  is 
  not 
  likely 
  to 
  be 
  due 
  to 
  the 
  presence 
  of 
  

   some 
  more 
  easily 
  soluble 
  substances 
  as 
  impurities, 
  because 
  the 
  

   velocity 
  constants 
  ought 
  in 
  such 
  a 
  case 
  to 
  decrease 
  with 
  time, 
  

   instead 
  of 
  increasing. 
  

  

  2Q2 
  

  

  