﻿512 
  Method 
  of 
  Measuring 
  large 
  Molecular 
  Masses. 
  

  

  N 
  15-64, 
  22-60, 
  S 
  0*76, 
  and 
  P 
  0*80, 
  and 
  with 
  16 
  for 
  

   the 
  atomic 
  B 
  o£ 
  P 
  we 
  can 
  write 
  down 
  the 
  corresponding 
  

   formula 
  for 
  the 
  casein 
  ion, 
  but 
  it 
  is 
  better 
  to 
  derive 
  this 
  

   from 
  the 
  experimental 
  equivalent 
  of 
  casein, 
  as 
  is 
  done 
  

   below. 
  

  

  If 
  v=2, 
  as 
  in 
  the 
  case 
  of 
  globulin, 
  the 
  equivalent 
  of 
  casein 
  

   is 
  1302. 
  Now 
  Laqueur 
  and 
  Sackur 
  found 
  1135 
  for 
  the 
  

   equivalent 
  of 
  casein 
  in 
  its 
  NaOH 
  compound 
  using 
  phenol- 
  

   phthalein 
  as 
  indicator. 
  The 
  calculated 
  result, 
  as 
  regards 
  order 
  

   of 
  magnitude, 
  is 
  in 
  satisfactory 
  agreement 
  with 
  this. 
  Hence 
  

   the 
  casein 
  ion 
  appears 
  to 
  be 
  divalent, 
  and 
  its 
  molecular 
  mass 
  

   by 
  titration 
  is 
  1135 
  x 
  2 
  or 
  2270. 
  According 
  to 
  the 
  per- 
  

   centage 
  composition 
  of 
  casein 
  and 
  2270 
  for 
  the 
  mass 
  of 
  its 
  

   ion 
  the 
  formula 
  of 
  its 
  ion 
  is 
  half 
  of 
  CsooH^NgoO^SP, 
  and 
  as 
  

   we 
  have 
  seen 
  by 
  analogy 
  with 
  globulin 
  the 
  casein 
  ions 
  must 
  

   be 
  derived 
  in 
  pairs 
  from 
  the 
  casein 
  molecule, 
  the 
  formula 
  

   just 
  given 
  is 
  the 
  simplest 
  possible 
  according 
  to 
  physical 
  

   considerations. 
  It 
  is 
  also 
  the 
  simplest 
  according 
  to 
  purely 
  

   chemical 
  considerations, 
  as 
  the 
  S 
  atom 
  or 
  the 
  P 
  atom 
  cannot 
  

   be 
  divided. 
  When 
  we 
  speak 
  of 
  the 
  casein 
  ion 
  being 
  half 
  of 
  

   this 
  formula 
  we 
  mean 
  the 
  average 
  casein 
  ion, 
  the 
  S 
  may 
  go 
  

   with 
  one 
  of 
  the 
  ions 
  and 
  P 
  with 
  the 
  other, 
  or 
  both 
  S 
  and 
  P 
  

   may 
  be 
  in 
  one 
  ion 
  and 
  neither 
  of 
  them 
  in 
  the 
  other, 
  the 
  mean 
  

   ion 
  always 
  containing 
  JS 
  and 
  ^P. 
  In 
  the 
  same 
  way 
  ihe 
  

   formula 
  of 
  the 
  globulin 
  ion 
  is 
  half 
  of 
  C 
  ]024 
  H 
  16 
  3 
  4 
  N 
  264 
  O 
  340 
  S 
  8 
  ,, 
  

   which 
  we 
  take 
  to 
  be 
  the 
  formula 
  for 
  the 
  globulin 
  molecule. 
  

   My 
  previous 
  estimate 
  was 
  dearly 
  double 
  this 
  (loo. 
  cit,). 
  

   According 
  to 
  the 
  theory 
  of 
  the 
  colloidal 
  state 
  proposed 
  by 
  

   me 
  in 
  ' 
  The 
  Chemistry 
  of 
  Globulin 
  ' 
  (loc. 
  cit.) 
  colloidal 
  glo- 
  

   bulin 
  and 
  casein 
  will 
  have 
  the 
  molecules 
  which 
  are 
  given 
  by 
  

   their 
  formulas 
  not 
  present 
  as 
  free 
  molecules, 
  but 
  as 
  those 
  

   three-dimensional 
  patterns 
  proposed 
  to 
  be 
  called 
  semplars^ 
  

   which 
  are 
  joined 
  symmetrically 
  to 
  one 
  another 
  by 
  some 
  of 
  

   the 
  latent 
  valencies 
  of 
  N 
  and 
  O 
  being 
  called 
  into 
  action. 
  

   For 
  a 
  full 
  account 
  of 
  many 
  previous 
  methods 
  of 
  estimating 
  

   the 
  mass 
  of 
  large 
  protein 
  molecules 
  the 
  reader 
  is 
  referred 
  to 
  

   Die 
  Grosse 
  des 
  Eiweissmolekuls 
  by 
  F. 
  N. 
  Schulz 
  (Jena. 
  

   G. 
  Fischer, 
  1903). 
  

  

  Melbourne, 
  May 
  1908. 
  

  

  