﻿MAY 
  4, 
  1922 
  morEy: 
  crystallization 
  pressure 
  in 
  magmas 
  223 
  

  

  of 
  the 
  KNO3 
  about 
  3° 
  C. 
  With 
  the 
  liquid 
  saturated 
  at 
  this 
  tempera- 
  

   ture, 
  suppose 
  the 
  apparatus 
  to 
  be 
  closed 
  in 
  such 
  a 
  manner 
  that 
  the 
  

   vapor 
  space 
  is 
  very 
  small, 
  and 
  the 
  cooling 
  to 
  be 
  continued, 
  then 
  

   crystallization 
  of 
  KNO3 
  will 
  begin 
  at 
  about 
  3 
  ° 
  below 
  its 
  own 
  freezing 
  

   point. 
  As 
  the 
  mixture 
  cools, 
  crystallization 
  proceeds, 
  the 
  water 
  con- 
  

   tent 
  of 
  the 
  mixture 
  increases, 
  and 
  its 
  vapor 
  pressure 
  rises. 
  Reference 
  

   to 
  figure 
  1, 
  A 
  or 
  B, 
  shows 
  that 
  at 
  the 
  time 
  crystallization 
  begins, 
  the 
  

   liquid 
  composition 
  is 
  99 
  per 
  cent 
  KNO3, 
  1 
  per 
  cent 
  H2O. 
  When 
  the 
  

   water 
  content 
  has 
  doubled, 
  the 
  pressure 
  has 
  increased 
  from 
  1 
  atmos- 
  

   phere 
  to 
  over 
  6 
  atmospheres, 
  a 
  six-fold 
  increase. 
  When 
  the 
  water 
  

   content 
  has 
  again 
  doubled, 
  reaching 
  4 
  per 
  cent, 
  the 
  pressure 
  has 
  risen 
  

   to 
  almost 
  11 
  atmospheres. 
  If 
  the 
  mixture 
  be 
  contained 
  in 
  a 
  flask 
  

   which 
  can 
  withstand 
  a 
  pressure 
  of 
  only 
  10 
  atmospheres, 
  the 
  flask 
  will 
  

   burst, 
  as 
  the 
  result 
  of 
  the 
  pressure 
  developed 
  by 
  cooling 
  the 
  mixture. 
  

  

  Similar 
  relations 
  hold 
  in 
  silicate 
  systems. 
  It 
  is 
  now 
  a 
  demonstrated 
  

   fact 
  that 
  water 
  vapor 
  under 
  a 
  pressure 
  of 
  one 
  atmosphere 
  is 
  appreciably 
  

   soluble 
  in 
  liquid 
  silicates 
  at 
  their 
  melting 
  points, 
  and 
  that 
  the 
  amount 
  

   of 
  water 
  dissolved 
  at 
  this 
  pressure 
  will 
  produce 
  an 
  appreciable 
  lowering 
  

   of 
  the 
  melting 
  point. 
  In 
  other 
  words, 
  the 
  melting 
  point 
  as 
  determined 
  

   in 
  steam 
  at 
  one 
  atmosphere 
  pressure 
  is 
  appreciably 
  lower 
  than 
  that 
  

   determined 
  in 
  air 
  in 
  the 
  usual 
  manner, 
  just 
  as 
  was 
  the 
  case 
  with 
  KNO3. 
  

   In 
  the 
  case 
  of 
  anorthite, 
  about 
  0.1 
  per 
  cent 
  of 
  H2O 
  is 
  dissolved, 
  and 
  the 
  

   freezing 
  point 
  is 
  lowered 
  about 
  5°. 
  If 
  the 
  initial 
  pressure 
  of 
  water 
  

   vapor 
  is 
  increased, 
  more 
  water 
  will 
  be 
  dissolved 
  and 
  freezing 
  will 
  begin 
  

   at 
  a 
  correspondingly 
  lower 
  temperature. 
  In 
  the 
  case 
  of 
  KNO3, 
  

   increase 
  in 
  the 
  water 
  content 
  from 
  1 
  to 
  4 
  per 
  cent 
  corresponded 
  to 
  an 
  

   increase 
  of 
  pressure 
  from 
  about 
  1 
  to 
  over 
  11 
  atmospheres. 
  In 
  the 
  

   case 
  of 
  a 
  system 
  such 
  as 
  H20-Si02 
  the 
  maximum 
  pressure 
  would 
  prob- 
  

   ably 
  be 
  reached 
  at 
  a 
  smaller 
  H2O 
  content, 
  and 
  its 
  magnitude 
  would 
  

   probably 
  be 
  enormous. 
  Likewise, 
  the 
  pressure 
  which 
  would 
  be 
  de- 
  

   veloped 
  by 
  a 
  magma 
  containing 
  but 
  a 
  small 
  amount 
  of 
  H2O, 
  cooled 
  in 
  

   such 
  a 
  manner 
  that 
  this 
  water 
  could 
  not 
  escape, 
  as 
  is 
  doubtless 
  often- 
  

   times 
  the 
  case, 
  would 
  be 
  very 
  great 
  indeed. 
  

  

  Before 
  considering 
  this 
  phase 
  of 
  the 
  subject 
  further, 
  some 
  known 
  

   examples 
  showing 
  the 
  reality 
  of 
  the 
  phenomenon 
  will 
  be 
  given. 
  When 
  

   liquid 
  KNO3 
  is 
  saturated 
  with 
  water 
  at 
  one 
  atmosphere 
  pressure, 
  and 
  

   the 
  mixture 
  cooled, 
  at 
  a 
  certain 
  temperature 
  solid 
  KNO3 
  will 
  begin 
  to 
  

   separate 
  from 
  the 
  liquid. 
  If 
  the 
  vessel 
  be 
  open 
  to 
  the 
  air, 
  the 
  pres- 
  

   sure 
  cannot 
  rise 
  above 
  one 
  atmosphere, 
  so 
  the 
  water 
  will 
  pass 
  off 
  as 
  

   steam 
  ; 
  the 
  liquid 
  will 
  evaporate 
  to 
  dryness, 
  giving 
  rise 
  to 
  solid 
  and 
  

  

  