﻿498 
  C. 
  Barm 
  — 
  The 
  Contraction 
  of 
  Molten 
  Rock. 
  

  

  always 
  very 
  small, 
  and 
  occasionally 
  scarcely 
  appreciable. 
  The 
  

   isomorphism 
  of 
  ammonium 
  sulphate, 
  mascagnite, 
  with 
  barite 
  

   is 
  worthy 
  of 
  notice. 
  

  

  When 
  the 
  powdered 
  white 
  or 
  yellow 
  material 
  is 
  heated 
  in 
  a 
  

   closed 
  tube 
  an 
  appreciable 
  sublimate 
  of 
  ammonium 
  salts 
  is 
  

   obtained 
  and 
  at 
  the 
  same 
  time 
  an 
  empyreumatic 
  odor 
  is 
  notice- 
  

   able. 
  It 
  was 
  thought 
  that 
  perhaps 
  the 
  sublimate 
  might 
  be 
  due 
  

   to 
  the 
  decomposition 
  of 
  nitrogenous 
  organic 
  matter 
  by 
  the 
  

   heat 
  employed. 
  That 
  this 
  was 
  not 
  the 
  case 
  was 
  proved 
  by 
  the 
  

   fact 
  that 
  it 
  was 
  possible 
  by 
  cold 
  extraction 
  with 
  water 
  to 
  obtain 
  

   very 
  decided 
  Nessler 
  reactions 
  for 
  ammonia. 
  It 
  is 
  therefore 
  

   assumed 
  by 
  the 
  writers 
  that 
  the 
  ammonium 
  occurs 
  as 
  mascag- 
  

   nite 
  in 
  association 
  with 
  the 
  other 
  sulphates. 
  

  

  Specimens 
  of 
  these 
  Pettis 
  Co. 
  barites 
  were 
  sent 
  to 
  Mr. 
  F. 
  

   W. 
  Clarke, 
  of 
  the 
  chemical 
  department 
  of 
  the 
  U. 
  S. 
  Geological 
  

   Survey, 
  and 
  were 
  kindly 
  examined 
  by 
  Dr. 
  W. 
  F. 
  Rillebrand, 
  

   who 
  confirms 
  the 
  presence 
  of 
  ammonia. 
  Mr. 
  J. 
  S. 
  Diller, 
  of 
  

   the 
  U. 
  S. 
  Geological 
  Survey, 
  also 
  examined 
  them 
  microscopi- 
  

   cally 
  and 
  finds 
  that 
  the 
  opacity 
  is 
  probably 
  due 
  to 
  the 
  presence 
  

   of 
  myriads 
  of 
  cavities 
  which 
  seem 
  to 
  be 
  tilled 
  with 
  air. 
  

  

  We 
  wish 
  to 
  herewith 
  express 
  our 
  thanks 
  to 
  these 
  gentlemen, 
  

   as 
  well 
  as 
  also 
  to 
  Dr. 
  Hambach 
  of 
  St. 
  Louis 
  and 
  Mr. 
  Sampson 
  

   of 
  Sedalia 
  for 
  samples 
  furnished. 
  

  

  Art. 
  LV. 
  — 
  The 
  Contraction 
  of 
  Molten 
  Rock; 
  by 
  C. 
  Barus. 
  

  

  At 
  the 
  request 
  of 
  Mr. 
  Clarence 
  King 
  I 
  made 
  the 
  following 
  

   volume 
  measurements 
  on 
  a 
  sample 
  of 
  diabase 
  which 
  he 
  fur- 
  

   nished. 
  In 
  the 
  method 
  employed, 
  both 
  the 
  contraction 
  of 
  the 
  

   rock 
  and 
  of 
  the 
  vessel 
  containing 
  it, 
  were 
  measured 
  simulta- 
  

   neously, 
  and 
  cooling 
  was 
  conducted 
  so 
  slowly 
  that 
  the 
  viscosity 
  

   of 
  the 
  latter 
  remained 
  indefinitely 
  high 
  relatively 
  to 
  the 
  

   former, 
  throughout. 
  Four 
  series 
  of 
  data 
  are 
  in 
  hand, 
  the 
  

   last 
  two 
  of 
  which 
  are 
  full 
  and 
  satisfactory. 
  Thus 
  if 
  3a 
  be 
  the 
  

   mean 
  coefficient 
  of 
  actual 
  volume 
  expansion 
  (or 
  contraction), 
  

   and 
  3/3 
  be 
  the 
  actual 
  volume 
  decrement 
  on 
  solidifying, 
  where 
  

   both 
  3a 
  and 
  3/3 
  are 
  referred 
  to 
  the 
  unit 
  of 
  volume 
  of 
  solid 
  rock 
  

   at 
  zero 
  centigrade, 
  I 
  found 
  in 
  the 
  third 
  series 
  between 
  0° 
  and 
  

   1000°, 
  3a 
  = 
  250/10 
  7 
  ; 
  between 
  1100° 
  and 
  1500°, 
  3a 
  = 
  470/10 
  7 
  ; 
  

   at 
  1095°, 
  3/3= 
  +39/10 
  3 
  ; 
  and 
  in 
  the 
  fourth 
  series, 
  similarly, 
  

   3a 
  = 
  250/10 
  7 
  , 
  3a 
  = 
  468/10 
  7 
  , 
  3/3 
  = 
  + 
  U/W, 
  respectively. 
  Fu- 
  

   sion 
  of 
  igneous 
  rock 
  (diabase) 
  is 
  therefore 
  not 
  only 
  quite 
  normal 
  

   in 
  type, 
  but 
  sharp 
  at 
  a 
  definite 
  melting 
  point. 
  Thus 
  the 
  volume 
  

   increments 
  (v 
  t 
  — 
  v 
  )/v 
  , 
  at 
  consecutive 
  temperatures, 
  t, 
  during 
  

  

  