﻿422 
  Scientific 
  Intelligence. 
  

  

  was 
  observed 
  before 
  crystallisation 
  took 
  place. 
  When 
  the 
  crys- 
  

   tallisation 
  of 
  this 
  solution 
  is 
  finished, 
  the 
  sum 
  of 
  the 
  volumes 
  of 
  

   the 
  crystals 
  and 
  the 
  mother-liquor 
  is 
  less 
  than 
  that 
  of 
  the 
  original 
  

   supersaturated 
  solution. 
  The 
  state 
  of 
  unrest 
  which 
  precedes 
  the 
  

   actual 
  appearance 
  of 
  the 
  first 
  crystal 
  consists 
  in 
  a 
  rhythmic 
  series 
  

   of 
  isothermal 
  expansions 
  and 
  contractions, 
  which 
  cease 
  the 
  

   moment 
  the 
  first 
  crystal 
  appears 
  and 
  heat 
  is 
  liberated. 
  The 
  

   supersaturated 
  solution 
  exhibits 
  veritable 
  symptoms 
  of 
  labour 
  

   before 
  giving 
  birth 
  to 
  the 
  crystals 
  and 
  becoming 
  itself 
  a 
  mother- 
  

   liquor." 
  h. 
  s. 
  u. 
  

  

  9. 
  Die 
  elektrischen 
  Eigenschaften 
  und 
  die 
  JBedeutung 
  des 
  

   Selensfilr 
  die 
  Elektrotechnik 
  • 
  by 
  Dr. 
  Chr. 
  Ries. 
  Second 
  edi- 
  

   tion. 
  Pp. 
  189, 
  with 
  90 
  figures. 
  Berlin-Nikolassee, 
  1913 
  (Admin- 
  

   istration 
  der 
  Fachzeitschrift 
  " 
  Der 
  Mechaniker 
  "). 
  — 
  The 
  present 
  

   edition 
  of 
  this 
  book 
  was 
  made 
  necessary 
  by 
  the 
  numerous 
  investi- 
  

   gations 
  of 
  the 
  properties 
  of 
  selenium, 
  and 
  by 
  the 
  great 
  improve- 
  

   ments 
  in 
  the 
  practical 
  applications 
  which 
  have 
  been 
  made 
  in 
  the 
  

   last 
  four 
  years. 
  Most 
  of 
  the 
  sections 
  have 
  been 
  rewritten 
  and 
  

   amplified 
  so 
  that 
  the 
  volume 
  has 
  grown 
  to 
  nearly 
  double 
  its 
  origi- 
  

   nal 
  size. 
  Chapters 
  I 
  to 
  XVII 
  inclusive 
  (pp. 
  1-130) 
  are 
  devoted 
  

   to 
  the 
  purely 
  physical 
  properties 
  of 
  selenium, 
  while 
  chapter 
  

   XVIII 
  (pp. 
  130-160) 
  deals 
  with 
  the 
  practical 
  applications 
  of 
  

   these 
  properties. 
  The 
  next 
  chapter 
  gives 
  the 
  complete 
  bibliogra- 
  

   phy 
  of 
  the 
  subject, 
  and 
  comprises 
  388 
  references 
  which 
  are 
  

   grouped 
  under 
  the 
  year 
  of 
  publication 
  and 
  then 
  arranged 
  alpha- 
  

   betically 
  according 
  to 
  the 
  names 
  of 
  the 
  authors. 
  The 
  material 
  is 
  

   presented 
  in 
  such 
  a 
  clear, 
  thorough 
  and 
  systematic 
  manner 
  that 
  

   the 
  book 
  constitutes 
  a 
  very 
  useful 
  and 
  interesting 
  contribution 
  to 
  

   the 
  subject. 
  h. 
  s. 
  u. 
  

  

  10. 
  Photochemische 
  Versuchstechnik 
  ; 
  by 
  Johannes 
  Plotni- 
  

   kow. 
  Pp. 
  xv, 
  371, 
  with 
  189 
  figures, 
  50 
  tables, 
  3 
  plates. 
  Leipzig, 
  

   1912 
  (Akademische 
  Verlagsgesellschaft). 
  — 
  Prior 
  to 
  the 
  appear- 
  

   ance 
  of 
  this 
  book 
  there 
  existed 
  no 
  single 
  volume 
  which 
  contained 
  

   a 
  description 
  of 
  the 
  methods 
  of 
  experimentation 
  and 
  of 
  the 
  appara- 
  

   tus 
  used 
  in 
  photochemical 
  investigations. 
  The 
  present 
  incom- 
  

   plete 
  development 
  of 
  the 
  subject 
  caused 
  the 
  author 
  to 
  state 
  clearly 
  

   in 
  his 
  preface 
  that 
  the 
  text 
  is 
  not 
  a 
  laboratory 
  manual 
  or 
  practical 
  

   guide 
  but 
  that, 
  in 
  the 
  nature 
  of 
  the 
  case, 
  it 
  deals 
  only 
  with 
  the 
  

   technique 
  of 
  experimentation. 
  The 
  value 
  of 
  the 
  book 
  is 
  greatly 
  

   enhanced 
  by 
  the 
  fact 
  that, 
  under 
  the 
  direct 
  supervision 
  of 
  Plotni- 
  

   kow, 
  the 
  firm 
  of 
  Fritz 
  Kohler 
  in 
  Leipzig 
  has 
  established 
  a 
  new 
  

   department 
  of 
  photochemical 
  apparatus. 
  Some 
  pieces 
  of 
  appara- 
  

   tus 
  are 
  new 
  and 
  are 
  described 
  for 
  the 
  first 
  time. 
  

  

  As 
  regards 
  details, 
  the 
  material 
  is 
  presented 
  in 
  a 
  very 
  thorough 
  

   and 
  admirable 
  manner. 
  The 
  first 
  four 
  Parts 
  of 
  the 
  text 
  deal 
  

   respectively 
  with 
  sources 
  of 
  light, 
  optical 
  thermostats, 
  optical 
  

   measuring 
  instruments, 
  and 
  photochemical 
  demonstration 
  experi- 
  

   ments. 
  The 
  fifth 
  Part 
  comprises 
  a 
  very 
  complete 
  set 
  of 
  numerical 
  

   tables. 
  Of 
  these, 
  the 
  tables 
  of 
  reciprocal 
  wave-lengths 
  and 
  of 
  

   e_x 
  deserve 
  special 
  mention. 
  The 
  bibliographical 
  references 
  are 
  

  

  