﻿426 
  Scientific 
  Intelligence. 
  

  

  and 
  pyrogallol 
  a 
  fine 
  violet 
  color. 
  Since 
  these 
  reactions 
  are 
  not 
  

   given 
  by 
  succinic, 
  malic, 
  citric 
  or 
  benzoic 
  acids, 
  tartaric 
  acid 
  may 
  

   readily 
  be 
  detected 
  when 
  mixed 
  with 
  any 
  of 
  these 
  acids. 
  To 
  de- 
  

   tect 
  0*01 
  milligram, 
  the 
  author 
  evaporates 
  the 
  solution 
  to 
  be 
  

   tested 
  to 
  dryness, 
  one 
  c.c. 
  of 
  the 
  resorcinal 
  solution 
  is 
  added, 
  and 
  

   the 
  whole 
  is 
  gradually 
  heated 
  to 
  about 
  125°. 
  At 
  first 
  reddish 
  

   streaks 
  appear 
  and 
  then 
  the 
  sulphuric 
  acid 
  becomes 
  colored 
  

   throughout. 
  If 
  organic 
  substances 
  which 
  char 
  with 
  sulphuric 
  

   acid 
  are 
  present, 
  the 
  tartaric 
  acid 
  is 
  removed 
  by 
  precipitation 
  as 
  

   lead 
  tartrate 
  and 
  then 
  tested, 
  nitrates 
  and 
  nitrites 
  should 
  not 
  be 
  

   present.— 
  Bull. 
  Soc. 
  Ohem., 
  Ill, 
  iv, 
  728 
  ; 
  J. 
  Chem. 
  Soc, 
  lx, 
  867, 
  

   July, 
  1891. 
  G. 
  r. 
  b. 
  

  

  6. 
  Photography 
  of 
  the 
  Spectrum 
  in 
  natural 
  color. 
  — 
  H. 
  W. 
  

   Vogel 
  gives 
  a 
  historical 
  account 
  of 
  the 
  photography 
  of 
  color 
  

   and 
  an 
  explanation 
  of 
  the 
  failures 
  to 
  accomplish 
  it. 
  It 
  appears 
  

   that 
  Zenker, 
  in 
  1868, 
  indicated 
  the 
  method 
  of 
  depositing 
  layers 
  

   of 
  silver 
  of 
  suitable 
  thickness 
  to 
  produce 
  by 
  interference 
  of 
  light 
  

   colored 
  photographs, 
  a 
  method 
  which 
  Lippman 
  has 
  lately 
  devel- 
  

   oped. 
  Lord 
  Rayleigh's 
  (1886) 
  explanation 
  of 
  the 
  colors 
  in 
  pho- 
  

   tographs 
  produced 
  by 
  adjusting 
  the 
  layers 
  of 
  silver 
  to 
  wave 
  

   lengths 
  in 
  order 
  to 
  produce 
  colors 
  by 
  interference 
  is 
  a 
  repetition 
  

   of 
  the 
  explanation 
  of 
  Zenker. 
  In 
  the 
  earlier 
  processes 
  Ag 
  2 
  Cl 
  was 
  

   used 
  in 
  the 
  sensitive 
  film 
  and 
  the 
  fixing 
  of 
  the 
  image 
  produced 
  in 
  

   this 
  film, 
  by 
  hyposulphite 
  of 
  soda, 
  destroyed 
  by 
  separation 
  of 
  fine 
  

   silver 
  particles 
  the 
  regular 
  layers 
  which 
  were 
  necessary 
  to 
  pro- 
  

   duce 
  interference 
  colors. 
  Lippman 
  uses 
  pure 
  bromide 
  of 
  silver 
  

   which, 
  under 
  the 
  operation 
  of 
  fixing, 
  leaves 
  the 
  film 
  in 
  homoge- 
  

   neous, 
  regular 
  layers 
  suitable 
  for 
  producing 
  interference 
  colors. 
  — 
  

  

  Verhandl. 
  d. 
  Physik. 
  Ges. 
  Berlin, 
  10, 
  p. 
  33, 
  1891 
  ; 
  Photogr. 
  

   Mittheil, 
  28, 
  p. 
  7. 
  j. 
  t. 
  

  

  7. 
  Discharge 
  of 
  Electricity 
  through 
  exhausted 
  Tubes 
  without 
  

   Electrodes. 
  — 
  J. 
  J. 
  Thomson 
  points 
  out 
  that 
  the 
  oscillations 
  of 
  

   the 
  discharge 
  from 
  a 
  Leyden 
  jar 
  produce 
  during 
  the 
  short 
  time 
  

   of 
  their 
  duration 
  enormous 
  currents 
  in 
  the 
  wire 
  connecting 
  the 
  

   coatings 
  of 
  the 
  jar, 
  and 
  therefore 
  produce 
  by 
  induction 
  very 
  

   great 
  electromotive 
  force 
  in 
  the 
  neighborhood 
  of 
  the 
  wire. 
  He 
  

   therefore 
  investigates 
  the 
  discharge 
  by 
  induction 
  in 
  rarefied 
  ves- 
  

   sels 
  by 
  wrapping 
  these 
  vessels 
  with 
  the 
  wire 
  connecting 
  the 
  coat- 
  

   ings 
  of 
  a 
  Leyden 
  jar 
  ; 
  thus 
  producing 
  luminous 
  discharges 
  in 
  

   these 
  vessels 
  without 
  the 
  direct 
  passage 
  of 
  electricity 
  from 
  metal- 
  

   lic 
  terminals 
  in 
  the 
  gas. 
  Professor 
  Thomson 
  points 
  out 
  that 
  the 
  

   phenomena 
  bear 
  upon 
  his 
  theory 
  of 
  tubes 
  of 
  electrostatic 
  induction. 
  

   He 
  regards 
  the 
  distinction 
  between 
  electrostatic 
  and 
  electromag- 
  

   netic 
  electromotive 
  forces 
  as 
  one 
  introduced 
  for 
  convenience 
  of 
  

   analysis 
  rather 
  than 
  as 
  having 
  any 
  physical 
  reality. 
  "The 
  only 
  

   difference 
  which 
  -could 
  be 
  made, 
  from 
  a 
  physical 
  point 
  of 
  view, 
  

   would 
  be 
  to 
  define 
  those 
  effects 
  as 
  electrostatic 
  which 
  are 
  due 
  to 
  

   tubes 
  of 
  electrostatic 
  induction 
  having 
  free 
  ends, 
  and 
  to 
  confine 
  

   the 
  term 
  electromagnetic 
  to 
  the 
  effects 
  produced 
  by 
  closed 
  endless 
  

   tubes. 
  It 
  is 
  only 
  when 
  the 
  electromotive 
  forces 
  are 
  produced 
  ex- 
  

  

  