﻿MAY 
  4, 
  1922 
  MOREY: 
  CRYSTALLIZATION 
  PRESSURE 
  IN 
  MAGMAS 
  229 
  

  

  tween 
  will 
  be 
  a 
  surface 
  at 
  which 
  the 
  water 
  is 
  boiling. 
  The 
  location 
  

   of 
  this 
  zone 
  of 
  boiling 
  will 
  be 
  determined 
  by 
  the 
  hydrostatic 
  head 
  of 
  

   the 
  water; 
  if 
  the 
  head 
  is 
  about 
  3000 
  feet, 
  the 
  hydrostatic 
  head 
  will 
  be 
  

   about 
  100 
  atmospheres, 
  and 
  the 
  zone 
  of 
  boiling 
  will 
  be 
  removed 
  to 
  

   a 
  region 
  in 
  which 
  the 
  temperature 
  is 
  about 
  310°. 
  

  

  When 
  the 
  magma 
  crystallizes, 
  the 
  water 
  dissolved 
  in 
  it 
  at 
  a 
  pressure 
  of 
  

  

  100 
  atmospheres 
  will 
  be 
  concentrated, 
  and 
  the 
  pressure 
  may 
  increase 
  

  

  to 
  a 
  high 
  value, 
  as 
  previously 
  explained. 
  If 
  eruption, 
  with 
  release 
  of 
  

  

  pressure, 
  takes 
  place, 
  we 
  have 
  the 
  water, 
  absorbed 
  under 
  a 
  pressure 
  of 
  

  

  100 
  atmospheres, 
  being 
  released 
  under 
  a 
  pressure 
  many 
  times 
  100 
  

  

  atmospheres. 
  The 
  crystallization 
  may 
  take 
  place 
  at 
  some 
  distance 
  

  

  from 
  the 
  point 
  of 
  entry 
  of 
  the 
  water, 
  under 
  conditions 
  such 
  that 
  the 
  

  

  back 
  pressure 
  developed 
  by 
  the 
  crystallizing 
  liquid 
  does 
  not 
  reach 
  the 
  

  

  porous 
  strata 
  which 
  were 
  the 
  source 
  of 
  the 
  water, 
  or 
  the 
  suddenness 
  

  

  with 
  which 
  the 
  pressure 
  is 
  developed 
  may 
  be 
  such 
  that 
  the 
  tortuous 
  

  

  channels 
  in 
  the 
  porous 
  strata 
  offer 
  a 
  greater 
  resistance 
  to 
  its 
  release 
  

  

  than 
  does 
  the 
  overlying 
  crust 
  or 
  lava 
  column. 
  It 
  is 
  highly 
  probable 
  

  

  that 
  if 
  such 
  lava 
  were 
  to 
  be 
  forced 
  into 
  the 
  water-saturated 
  porous 
  

  

  •strata 
  it 
  would 
  effectually 
  seal 
  itself 
  by 
  rapid 
  cooling 
  in 
  the 
  pore 
  spaces. 
  

  

  The 
  solubility 
  of 
  water 
  in 
  a 
  silicate 
  melt 
  at 
  a 
  given 
  pressure 
  of 
  water 
  

   vapor 
  will 
  depend 
  largely 
  on 
  the 
  temperature, 
  and 
  it 
  is 
  to 
  be 
  ex- 
  

   pected 
  that 
  the 
  solubility 
  will 
  increase 
  with 
  decreasing 
  temperature, 
  

   for 
  the 
  same 
  reasons 
  that 
  gases 
  are 
  more 
  soluble 
  in 
  cold 
  water 
  than 
  

   in 
  hot 
  water. 
  If 
  an 
  undercooled 
  silicate 
  mixture, 
  that 
  is, 
  a 
  mixture 
  

   which 
  had 
  remained 
  liquid 
  altho 
  it 
  had 
  cooled 
  below 
  the 
  temperature 
  

   at 
  which 
  crystallization 
  should 
  have 
  taken 
  place, 
  were 
  to 
  come 
  into 
  

   contact 
  with 
  water 
  vapor, 
  say 
  at 
  a 
  pressure 
  of 
  water 
  vapor 
  of 
  100 
  

   atmospheres 
  as 
  before, 
  it 
  would 
  probably 
  take 
  up 
  a 
  much 
  larger 
  

   quantity 
  of 
  water 
  than 
  at 
  a 
  high 
  temperature. 
  Reference 
  to 
  the 
  curve 
  

   ■ay 
  in 
  figure 
  1, 
  C 
  will 
  illustrate 
  this 
  point. 
  

  

  When 
  the 
  mixture 
  of 
  composition 
  y 
  is 
  cooled, 
  at 
  Ty 
  its 
  vapor 
  pres- 
  

   sure 
  is 
  5.1 
  atmospheres; 
  if 
  it 
  be 
  undercooled 
  to 
  Ty', 
  its 
  vapor 
  pressure 
  

   will 
  fall 
  to 
  4 
  atmospheres. 
  If 
  a 
  mixture 
  richer 
  in 
  water 
  is 
  under- 
  

   cooled, 
  its 
  pressure 
  will 
  fall 
  to 
  4 
  atmospheres 
  at 
  a 
  lower 
  temperature, 
  

   Ty". 
  vSimilarly, 
  the 
  pressure 
  of 
  4 
  atmospheres 
  will 
  correspond 
  to 
  

   progressively 
  lower 
  temperature 
  for 
  mixtures 
  of 
  increasingly 
  greater 
  

   water 
  content. 
  If, 
  now, 
  liquid 
  KNO3 
  be 
  undercooled 
  to 
  Ty", 
  under 
  

   a 
  water- 
  vapor 
  pressure 
  of 
  4 
  atmospheres 
  it 
  will 
  dissolve 
  not 
  the 
  amount 
  

   of 
  water 
  it 
  would 
  have 
  dissolved 
  at 
  its 
  saturation 
  temperature 
  Ty, 
  but 
  

   the 
  larger 
  amount 
  corresponding 
  to 
  the 
  mixture 
  whose 
  melting 
  point 
  

  

  