﻿AND 
  FORCING 
  AIR 
  PUMP. 
  387 
  

  

  with 
  valve 
  cocks 
  as 
  at 
  K 
  L, 
  in 
  order 
  to 
  allow 
  various 
  experiments 
  to 
  

   be 
  performed 
  by 
  means 
  of 
  the 
  tube 
  in 
  the 
  axis, 
  surmounted 
  by 
  a 
  cup 
  

   of 
  copper. 
  The 
  tube 
  being 
  open 
  at 
  the 
  lower 
  end, 
  the 
  cup 
  is 
  accessible 
  

   to 
  an 
  incandescent 
  iron. 
  The 
  contrivance 
  facilitates 
  the 
  exposure 
  of 
  

   substances 
  to 
  heat, 
  either 
  in 
  vacuo, 
  or 
  in 
  any 
  gas. 
  When 
  boric 
  acid 
  

   and 
  potassium 
  are 
  thus 
  heated, 
  boron 
  is 
  evolved. 
  By 
  means 
  of 
  a 
  simi- 
  

   lar 
  arrangement, 
  heating 
  chloride 
  of 
  calcium 
  with 
  potassium, 
  I 
  ob- 
  

   tained 
  a 
  potassuret 
  of 
  calcium, 
  which 
  decomposed 
  water 
  and 
  yielded 
  

   a 
  solution 
  which 
  was 
  rendered 
  milky 
  by 
  carbonic 
  acid. 
  

  

  When 
  a 
  glass 
  globe 
  of 
  fifteen 
  gallons 
  is 
  exhausted 
  over 
  this 
  plate, 
  

   and 
  filled 
  with 
  oxygen 
  gas, 
  phosphorus 
  having 
  been 
  previously 
  placed 
  

   in 
  the 
  copper 
  cup, 
  on 
  heating 
  the 
  phosphorus, 
  a 
  combustion 
  ensues 
  of 
  

   transcendent 
  splendour. 
  

  

  For 
  this 
  and 
  other 
  experiments, 
  the 
  hollow 
  cylinder, 
  which 
  supports 
  

   the 
  air 
  pump 
  plate, 
  may 
  be 
  screwed 
  into 
  a 
  hole 
  in 
  a 
  table 
  and 
  placed 
  

   at 
  any 
  convenient 
  distance 
  from 
  the 
  air 
  pump. 
  With 
  this 
  view, 
  there 
  

   is 
  a 
  conical 
  screw 
  cut 
  upon 
  the 
  lower 
  end 
  of 
  the 
  cylinder. 
  

  

  The 
  mechanism 
  by 
  which 
  the 
  piston 
  is 
  moved, 
  is 
  too 
  obvious 
  to 
  need 
  

   description. 
  There 
  is, 
  however, 
  a 
  peculiarity 
  in 
  the 
  construction 
  of 
  

   the 
  piston 
  rod, 
  which 
  is 
  of 
  great 
  utility. 
  The 
  rod 
  is 
  hollow, 
  having 
  

   been 
  sufficiently 
  reduced 
  in 
  diameter 
  from 
  a 
  piece 
  of 
  gun 
  barrel 
  by 
  

   the 
  wire 
  drawing 
  process. 
  The 
  bore 
  of 
  this 
  hollow 
  rod 
  is 
  occupied 
  

   by 
  a 
  solid 
  rod, 
  which 
  extends 
  from 
  the 
  metallic 
  disk, 
  at 
  the 
  farther 
  

   end 
  of 
  the 
  piston, 
  to 
  the 
  rack. 
  To 
  the 
  other 
  disk, 
  the 
  hollow 
  rod 
  is 
  

   fastened. 
  The 
  leather 
  packing 
  between 
  the 
  disks, 
  being 
  turned 
  in 
  the 
  

   lathe 
  so 
  as 
  to 
  fit 
  the 
  calibre 
  of 
  the 
  chamber 
  accurately, 
  is 
  made 
  more 
  

   or 
  less 
  tight 
  by 
  the 
  action 
  of 
  a 
  screw 
  just 
  above 
  the 
  rack. 
  Hence 
  the 
  

   pressure 
  may 
  be 
  regulated 
  without 
  taking 
  the 
  pump 
  apart, 
  which 
  is 
  

   always 
  troublesome, 
  and, 
  at 
  some 
  periods 
  impracticable 
  within 
  the 
  

   time 
  at 
  command. 
  

  

  With 
  respect 
  to 
  the 
  efficacy 
  of 
  this 
  pump, 
  satisfactory 
  proof 
  was 
  

   given 
  some 
  time 
  since, 
  at 
  the 
  Franklin 
  Institute, 
  when 
  it 
  raised 
  the 
  

   mercury 
  very 
  near 
  to 
  the 
  height 
  of 
  that 
  in 
  the 
  Torricellian 
  tube. 
  

  

  Having 
  been 
  in 
  possession 
  for 
  many 
  } 
  7 
  ears 
  of 
  an 
  elegant 
  air 
  pump 
  

   with 
  glass 
  chambers 
  furnished 
  by 
  Pixii, 
  we 
  have 
  been 
  induced 
  (o 
  give 
  

   vol. 
  v. 
  — 
  4 
  Y 
  

  

  