﻿Measuring 
  large 
  Molecular 
  Masses. 
  503 
  

  

  as 
  1, 
  2, 
  and 
  3. 
  To 
  each 
  value 
  of 
  B 
  corresponds 
  a 
  value 
  of 
  

   the 
  gram-molecular 
  mass 
  of 
  the 
  ion. 
  But 
  the 
  equivalent 
  

   mass 
  of 
  the 
  ion 
  is 
  generally 
  known 
  from 
  a 
  titration, 
  and 
  this 
  

   compared 
  with 
  the 
  values 
  of 
  M 
  shows 
  what 
  must 
  be 
  the 
  right 
  

   value 
  of 
  v, 
  and 
  so 
  the 
  right 
  value 
  of 
  M 
  is 
  obtained. 
  But 
  (10) 
  

   applies 
  strictly 
  only 
  to 
  the 
  pyridinecarboxylic 
  acids, 
  where 
  

   there 
  is 
  an 
  amphoteric 
  union 
  of 
  basic 
  and 
  acid 
  properties. 
  

   We 
  may 
  assume 
  (10) 
  and 
  (11) 
  to 
  apply 
  approximately 
  to 
  

   other 
  amphoteric 
  ions. 
  The 
  first 
  term 
  on 
  the 
  right 
  is 
  

   uncertain, 
  being 
  for 
  the 
  pyridinecarboxylic 
  acids 
  only 
  0*15 
  

   of 
  the 
  value 
  for 
  the 
  fatty 
  acids, 
  but 
  for 
  the 
  case 
  of 
  v 
  not 
  

   large 
  it 
  is 
  of 
  minor 
  importance. 
  Indeed, 
  in 
  these 
  equations 
  

   if 
  we 
  neglect 
  the 
  first 
  term 
  on 
  the 
  rio-ht 
  we 
  get 
  a 
  form 
  of 
  

   relation 
  corresponding 
  to 
  the 
  relation 
  v/B£A 
  = 
  X/280, 
  K 
  

   being 
  dielectric 
  capacity 
  of 
  ion, 
  which 
  I 
  used 
  when 
  first 
  

   proposing 
  to 
  find 
  the 
  mass 
  of 
  an 
  ion 
  from 
  its 
  conductivity. 
  

   For 
  the 
  large 
  organic 
  ions 
  K 
  — 
  2 
  nearly. 
  When 
  v 
  is 
  large 
  

   we 
  shall 
  have 
  to 
  proceed 
  in 
  a 
  similar 
  way 
  with 
  (11), 
  but 
  

   more 
  warily. 
  It 
  will 
  be 
  best 
  then 
  to 
  illustrate 
  the 
  method 
  

   by 
  applying 
  it 
  to 
  some 
  typical 
  cases. 
  

  

  The 
  most 
  interesting 
  group 
  is 
  that 
  of 
  the 
  peptones 
  shown 
  

   by 
  Siegfried 
  and 
  his 
  pupils 
  to 
  be 
  definite 
  chemical 
  substances 
  

   (Ber. 
  d. 
  Deutsch. 
  Chem. 
  Ges. 
  xxxiii. 
  ; 
  Zeitsch. 
  f. 
  phi/siolog. 
  

   Chem. 
  xxxv., 
  xxxviii., 
  xlv.). 
  The 
  following 
  are 
  filenames 
  

   of 
  these, 
  their 
  simplest 
  formulas 
  by 
  analysis, 
  and 
  the 
  corre- 
  

   sponding 
  provisional 
  molecular 
  weights 
  along 
  with 
  equivalents 
  

   discussed 
  below. 
  

  

  Equivalent 
  

  

  as 
  ac 
  

  

  Trypsinfibrinpeptone 
  a 
  ... 
  C 
  10 
  H 
  17 
  N 
  3 
  Os 
  

  

  13 
  ... 
  OuH^A 
  

  

  Pepsinfibrinpeptone 
  a 
  ... 
  C 
  il 
  H 
  34 
  X\ 
  ) 
  , 
  J 
  

  

  /3 
  ... 
  C 
  21 
  II 
  3r) 
  N 
  f) 
  O 
  10 
  

  

  Pepsinglntinpeptone 
  C 
  i3 
  H 
  39 
  ]S' 
  7 
  Oio 
  

  

  Trypsinglutinpeptcme 
  dgHgoNgOg 
  

  

  These 
  are 
  all 
  amphoteric, 
  but 
  their 
  acidic 
  character 
  is 
  more 
  

   pronounced 
  than 
  their 
  basic. 
  The 
  equivalent 
  weights 
  for 
  

   four 
  of 
  them 
  both 
  as 
  acids 
  and 
  bases 
  have 
  been 
  measured 
  by 
  

   Neumann 
  according 
  to 
  the 
  ingenious 
  method 
  of 
  electric 
  

   titration 
  devised 
  by 
  Sjoqvist 
  (Neumann, 
  Zeitsch. 
  f. 
  physiolog. 
  

   Chem. 
  xlv. 
  p. 
  216 
  ; 
  Sjoqvist, 
  Skand. 
  Archie 
  . 
  f. 
  Physiolog. 
  v. 
  

   1895). 
  This 
  method 
  depends 
  upon 
  the 
  exceptionally 
  large 
  

   electric 
  conductivities 
  of 
  the 
  H 
  ion 
  of 
  acids 
  and 
  of 
  the 
  OH 
  ion 
  

   of 
  alkalies. 
  Suppose 
  a 
  normal 
  solution 
  of 
  HC1 
  has 
  a 
  normal 
  

   solution 
  of 
  NaOH 
  added 
  to 
  it 
  in 
  instalments, 
  the 
  specific 
  

   electric 
  conductivity 
  of 
  the 
  mixture 
  being 
  measured 
  after 
  

  

  259 
  

  

  273 
  

  

  as 
  acid. 
  

   157 
  

  

  197 
  

  

  as 
  base 
  

   290 
  

   397 
  

  

  515 
  

  

  523 
  

  

  248 
  

  

  370 
  

  

  573 
  

   486 
  

  

  320 
  

  

  470 
  

  

  