﻿462 
  Mr. 
  J. 
  E. 
  Petavel 
  on 
  a 
  Recording 
  

  

  in 
  1743, 
  Hutton 
  in 
  1778, 
  and 
  Count 
  Bumford 
  in 
  1797. 
  

   Iiumford's 
  method 
  consisted 
  ill 
  determining 
  the 
  minimum 
  

   weight 
  required 
  to 
  prevent 
  a 
  valve 
  from 
  lifting 
  under 
  the 
  

   pressure 
  of: 
  the 
  explosion, 
  and 
  was 
  used, 
  with 
  slight 
  variations, 
  

   by 
  a 
  long 
  succession 
  o£ 
  investigators, 
  the 
  best 
  known 
  expe- 
  

   riments 
  being 
  those 
  carried 
  out 
  in 
  1867 
  by 
  Bunsen. 
  

  

  The 
  relative 
  strength 
  of 
  solid 
  explosives 
  was 
  in 
  these 
  early 
  

   days 
  estimated 
  by 
  the 
  two 
  following 
  methods 
  : 
  — 
  

  

  I. 
  Firing 
  them 
  in 
  a 
  closed 
  chamber 
  in 
  the 
  centre 
  of 
  a 
  

   block 
  of 
  lead, 
  the 
  permanent 
  increase 
  of 
  volume 
  of 
  the 
  

   chamber 
  being 
  taken 
  as 
  a 
  measure 
  of 
  the 
  explosive 
  force. 
  

  

  II. 
  By 
  measuring 
  the 
  angle 
  through 
  which 
  a 
  heavy 
  pen- 
  

   dulum 
  was 
  moved 
  when 
  acted 
  upon 
  by 
  the 
  explosion. 
  

  

  The 
  Bodman 
  gauge, 
  invented 
  in 
  1859, 
  was 
  improved 
  and 
  

   modified 
  some 
  ten 
  years 
  later 
  by 
  the 
  Committee 
  on 
  Explosives, 
  

   the 
  work 
  resulting 
  in 
  the 
  instrument 
  known 
  as 
  the 
  Orusher- 
  

   gauge 
  which 
  since 
  then 
  has 
  been 
  almost 
  exclusively 
  used. 
  A 
  

   piston 
  works 
  in 
  a 
  steel 
  cylinder 
  screwed 
  into 
  the 
  explosion- 
  

   chamber. 
  One 
  end 
  of 
  the 
  piston 
  is 
  exposed 
  to 
  the 
  pressure 
  of 
  

   the 
  explosion, 
  the 
  other 
  rests 
  on 
  a 
  short 
  copper 
  cylinder. 
  The 
  

   explosion 
  crushes 
  the 
  copper 
  by 
  an 
  amount 
  which 
  bears 
  a 
  

   known 
  relation 
  to 
  the 
  maximum 
  pressure 
  attained. 
  

  

  In 
  1875, 
  Noble 
  and 
  Abel 
  measured 
  the 
  explosive 
  pressure 
  

   of 
  gunpowder 
  by 
  determining 
  the 
  rate 
  of 
  acceleration 
  of 
  a 
  

   projectile. 
  

  

  In 
  recent 
  years 
  many 
  new 
  instruments 
  have 
  been 
  devised. 
  

   Le 
  Chatelier 
  and 
  Mallard 
  have 
  used 
  a 
  modification 
  of 
  the 
  

   Bourdon 
  gauge. 
  Vieille 
  has 
  used 
  a 
  piston 
  controlled 
  by 
  a 
  

   stiff 
  spring. 
  Noble 
  and 
  others 
  have 
  obtained 
  records 
  from 
  

   an 
  instrument 
  not 
  unlike 
  an 
  ordinary 
  steam-engine 
  indicator,. 
  

   the 
  initial 
  compression 
  of 
  the 
  spring 
  being, 
  however, 
  regulated 
  

   to 
  nearly 
  correspond 
  to 
  the 
  maximum 
  explosive 
  pressure. 
  

  

  Many 
  useful 
  results 
  have 
  been 
  obtained 
  by 
  causing 
  the 
  piston 
  

   of 
  the 
  ordinary 
  crusher-gauge 
  to 
  inscribe 
  its 
  rate 
  of 
  motion 
  on 
  

   a 
  revolving 
  cylinder. 
  

  

  Finally, 
  the 
  chemical 
  phenomena 
  which 
  occur 
  during 
  the 
  

   firing 
  of 
  the 
  charge, 
  and 
  the 
  rate 
  of 
  explosion 
  of 
  several 
  

   gaseous 
  mixtures, 
  have 
  been 
  most 
  carefully 
  studied 
  by 
  

   Berthelot 
  in 
  France 
  and 
  H. 
  B. 
  Dixon 
  in 
  this 
  country 
  .^^j^ 
  

  

  Theoretical 
  Consideration. 
  

  

  The 
  all 
  important 
  condition 
  for 
  a 
  gauge 
  destined 
  to 
  record 
  

   the 
  rise 
  and 
  fall 
  of 
  pressure 
  caused 
  by 
  an 
  explosion 
  is 
  that 
  its- 
  

   time-period 
  should 
  be 
  as 
  small 
  as 
  possible. 
  If 
  "A" 
  represent 
  

   the 
  force 
  required 
  to 
  produce 
  unit 
  deflexion 
  of 
  the 
  vibrating 
  

  

  