﻿220 
  JOURNAI. 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  9 
  

  

  circumstance 
  that 
  the 
  magmatic 
  liquid 
  is 
  at 
  a 
  temperature 
  far 
  above 
  the 
  

   critical 
  temperature 
  of 
  the 
  volatile 
  ingredients 
  is 
  without 
  significance 
  

   as 
  long 
  as 
  any 
  of 
  the 
  liquid 
  phase 
  remains 
  in 
  the 
  system. 
  The 
  system 
  

   H2O-KNO3 
  has 
  accordingly 
  been 
  chosen 
  to 
  illustrate 
  the 
  relations 
  be- 
  

   tween 
  the 
  variables, 
  pressure, 
  temperature 
  and 
  composition 
  in 
  a 
  sys- 
  

   tem 
  containing 
  both 
  volatile 
  and 
  non-volatile 
  components. 
  

  

  In 
  a 
  system 
  such 
  as 
  H2O-KNO3 
  it 
  is 
  well 
  known 
  that 
  the 
  solubility 
  

   or 
  fusion 
  curve 
  is 
  continuous 
  from 
  the 
  eutectic 
  or 
  cryohydrate 
  to 
  the 
  

   melting 
  point 
  of 
  each 
  component. 
  This 
  is 
  illustrated 
  in 
  figure 
  1, 
  C,- 
  

   in 
  which 
  E 
  is 
  the 
  eutectic, 
  or 
  cryohydrate, 
  AmE 
  the 
  freezing-point 
  

   curve 
  of 
  water 
  in 
  equilibrium 
  with 
  solutions 
  of 
  increasing 
  KNO3 
  con- 
  

   tent, 
  B^jE 
  the 
  freezing-point 
  curve 
  of 
  KNO3 
  in 
  equilibrium 
  with 
  solu- 
  

   tions 
  of 
  increasing 
  H2O 
  content. 
  While 
  with 
  mixtures 
  rich 
  in 
  KNO3 
  

   it 
  is 
  necessary 
  to 
  carry 
  out 
  solubility 
  experiments 
  inclosed 
  vessels 
  to 
  

   prevent 
  the 
  escape 
  of 
  the 
  water, 
  KNO3 
  and 
  water 
  are 
  both 
  compon- 
  

   ents 
  of 
  all 
  liquids 
  in 
  the 
  binary 
  system. 
  This 
  still 
  holds 
  true 
  when 
  

   component 
  B 
  has 
  a 
  melting 
  point 
  above 
  the 
  critical 
  temperature 
  of 
  

   water, 
  as 
  is 
  the 
  case 
  in 
  magmatic 
  solutions. 
  The 
  curves 
  showing 
  the 
  

   vapor 
  pressure 
  of 
  the 
  saturated 
  solutions 
  given 
  in 
  figure 
  1 
  , 
  C 
  are 
  like- 
  

   wise 
  continuous 
  from 
  the 
  eutectic 
  to 
  the 
  melting 
  point 
  of 
  components 
  

   A 
  and 
  B, 
  respectively, 
  and 
  in 
  the 
  case 
  of 
  the 
  solutions 
  in 
  equilibrium 
  

   with 
  the 
  component 
  of 
  higher 
  melting 
  point, 
  KNO3, 
  the 
  curve 
  must 
  

   rise 
  to 
  a 
  maximum 
  pressure 
  with 
  increase 
  in 
  temperature, 
  then 
  on 
  

   further 
  increase 
  in 
  temperature 
  the 
  pressure 
  must 
  fall 
  to 
  the 
  vapor 
  pres- 
  

   sure 
  of 
  the 
  higher 
  melting 
  component 
  at 
  its 
  melting 
  point, 
  or, 
  more 
  

   exactly, 
  its 
  triple 
  point. 
  This 
  is 
  shown 
  in 
  figure 
  1, 
  B, 
  in 
  which 
  the 
  curve 
  

   EBn, 
  is 
  the 
  vapor-pressure 
  curve 
  of 
  the 
  solutions 
  saturated 
  with 
  com- 
  

   ponent 
  B. 
  As 
  the 
  temperature 
  is 
  increased, 
  the 
  vapor 
  pressure 
  of 
  the 
  

   saturated 
  solution 
  is 
  determined 
  by 
  the 
  balance 
  between 
  two 
  opposing 
  

   tendencies. 
  One 
  of 
  these 
  is 
  the 
  increase 
  in 
  vapor 
  pressure 
  of 
  the 
  water 
  

   with 
  increasing 
  temperature; 
  this 
  is 
  opposed 
  by 
  the 
  decreasing 
  water 
  

   content 
  of 
  the 
  solutions, 
  and 
  at 
  the 
  point 
  of 
  maximum 
  pressure 
  the 
  

   two 
  effects 
  become 
  equal. 
  At 
  higher 
  temperatures, 
  the 
  second 
  effect 
  

   preponderates, 
  and 
  the 
  pressure 
  of 
  the 
  saturated 
  solution 
  decreases 
  with 
  

   increasing 
  temperature. 
  The 
  actual 
  ratio 
  of 
  the 
  non-volatile 
  to 
  the 
  

   volatile 
  component 
  at 
  the 
  point 
  of 
  maximum 
  pressure 
  is 
  equal 
  to 
  the 
  

  

  - 
  Fig. 
  1 
  is 
  drawn 
  to 
  scale 
  for 
  the 
  system 
  H2O-KNO3, 
  but 
  the 
  components 
  H2O 
  and 
  KNO3 
  

   are 
  represented 
  by 
  A 
  and 
  B, 
  respectively, 
  for 
  the 
  purpose 
  of 
  clearer 
  discussion 
  of 
  similar 
  

   relations 
  in 
  systems 
  containing 
  other 
  components. 
  Experimental 
  details 
  of 
  the 
  study 
  of 
  

   this 
  system 
  will 
  be 
  published 
  soon. 
  

  

  