﻿384 
  Scientific 
  Intelligence. 
  

  

  are 
  not 
  obtainable 
  even 
  transitorily 
  with 
  liquids 
  alone, 
  namely, 
  

   shrinkage 
  or 
  imbibition, 
  and 
  consequent 
  modifications 
  of 
  the 
  

   smooth 
  surfaces 
  of 
  revolution 
  presented 
  by 
  the 
  primary 
  vortex. 
  

  

  The 
  gelatin 
  sol 
  was 
  allowed 
  to 
  drop 
  into 
  the 
  coagulating 
  solu- 
  

   tion 
  through 
  the 
  air, 
  the 
  distance 
  from 
  the 
  orifice 
  of 
  the 
  dropper 
  

   to 
  the 
  free 
  surface 
  of 
  the 
  solution 
  having 
  various 
  values 
  up 
  to 
  

   about 
  15 
  mm. 
  In 
  the 
  first 
  series 
  of 
  experiments 
  the 
  gelatin 
  sols 
  

   were 
  usually 
  made 
  by 
  dissolving 
  14 
  grams 
  of 
  gelatin 
  in 
  100 
  cc. 
  of 
  

   water. 
  The 
  best 
  results 
  were 
  obtained 
  with 
  aqueous 
  solutions 
  of 
  

   aluminium 
  sulphate. 
  The 
  density 
  and 
  temperature 
  of 
  the 
  fixing 
  

   bath 
  had 
  to 
  be 
  regulated 
  and 
  controlled 
  with 
  the 
  greatest 
  care. 
  

   The 
  density 
  range 
  was 
  from 
  1026 
  to 
  1-035 
  grams 
  per 
  cc. 
  for 
  

   gelatin 
  sols 
  varying 
  from 
  10 
  to 
  14 
  per 
  cent. 
  The 
  temperature 
  

   influenced 
  the 
  results 
  more 
  through 
  the 
  viscosity 
  and 
  setting 
  

   velocity 
  than 
  through 
  the 
  density. 
  The 
  second 
  best 
  salt 
  was 
  

   found 
  to 
  be 
  ferrous 
  sulphate. 
  

  

  When 
  the 
  density 
  and 
  temperature 
  of 
  the 
  solution 
  were 
  practi- 
  

   cally 
  the 
  same 
  as 
  those 
  of 
  the 
  gelatin 
  sol, 
  and 
  when 
  the 
  orifice 
  

   (of 
  diameter 
  4 
  mm.) 
  was 
  close 
  to 
  the 
  free 
  surface 
  of 
  the 
  bath, 
  

   the 
  familiar 
  forms 
  of 
  the 
  ' 
  ' 
  hanging 
  drop 
  ' 
  ' 
  were 
  obtained 
  in 
  great 
  

   perfection. 
  These 
  configurations, 
  however, 
  differ 
  from 
  the 
  analo- 
  

   gous 
  forms 
  assumed 
  by 
  liquid 
  drops 
  in 
  one 
  significant 
  particu- 
  

   lar. 
  That 
  is, 
  the 
  outline 
  of 
  the 
  top 
  surface, 
  which 
  rests 
  in 
  the 
  

   free 
  surface 
  of 
  the 
  solution, 
  is 
  not 
  circular, 
  but 
  crenate 
  or 
  stellate, 
  

   owing 
  to 
  shrinkage, 
  and 
  the 
  crenated 
  cross-section 
  extends 
  down 
  

   the 
  neck 
  of 
  the 
  drop, 
  so 
  that 
  a 
  number 
  of 
  meridional 
  corrugations 
  

   or 
  ribs 
  are 
  formed. 
  

  

  This 
  feature 
  can 
  be 
  greatly 
  accentuated 
  either 
  by 
  slightly 
  

   reducing 
  the 
  density 
  of 
  the 
  solution 
  or 
  by 
  running 
  in 
  the 
  sol 
  more 
  

   rapidly, 
  so 
  that 
  the 
  weight 
  of 
  the 
  drop 
  increases 
  quickly 
  before 
  

   the 
  sol 
  has 
  had 
  time 
  to 
  set 
  completely. 
  In 
  this 
  way, 
  the 
  length 
  

   of 
  the 
  neck 
  can 
  be 
  increased 
  very 
  considerably, 
  while 
  at 
  the 
  

   same 
  time 
  shrinkage 
  becomes 
  more 
  pronounced 
  ; 
  the 
  cross-section 
  

   is 
  star- 
  or 
  cross-shaped, 
  while, 
  in 
  extreme 
  cases, 
  the 
  drop 
  may 
  

   hang 
  at 
  the 
  end 
  of 
  a 
  long 
  and 
  delicate 
  flat 
  band. 
  Shrinkage 
  at 
  

   different 
  distances 
  from 
  the 
  center 
  is 
  likewise 
  not 
  uniform, 
  so 
  

   that 
  the 
  ribs 
  of 
  a 
  single 
  band 
  become 
  crinkled, 
  showing 
  in 
  some 
  

   instances 
  a 
  very 
  striking 
  resemblance 
  to 
  the 
  "undulating 
  mem- 
  

   brane" 
  found 
  on 
  many 
  organisms. 
  

  

  If 
  single 
  drops 
  of 
  the 
  same 
  gelatin 
  sol, 
  at 
  temperatures 
  between 
  

   25° 
  and 
  30°, 
  are 
  allowed 
  to 
  fall 
  into 
  a 
  solution 
  of 
  aluminium 
  

   sulphate 
  having 
  a 
  density 
  of 
  1030 
  to 
  1032 
  at 
  18° 
  to 
  18-5°, 
  a 
  

   small 
  portion 
  of 
  the 
  drop 
  adheres 
  to 
  the 
  surface 
  of 
  the 
  bath 
  and 
  

   the 
  rest 
  develops 
  a 
  vortex 
  which 
  attains 
  its 
  final 
  shape 
  and 
  comes 
  

   to 
  rest 
  at 
  5 
  to 
  12 
  mm. 
  below 
  the 
  surface. 
  The 
  general 
  contour 
  is 
  

   now 
  that 
  of 
  the 
  vortex 
  "mushroom." 
  

  

  To 
  show 
  conclusively 
  that 
  the 
  formation 
  of 
  ribs 
  was 
  due 
  to 
  

   shrinkage, 
  the 
  author 
  tried 
  gum 
  arabic 
  sol, 
  thus 
  avoiding 
  the 
  

  

  