﻿1875.] 
  

  

  supposed 
  Changes 
  in 
  Basaltic 
  Veins, 
  

  

  551 
  

  

  seems 
  not 
  impossible 
  but 
  that 
  some 
  of 
  the 
  constituents 
  of 
  these 
  strata, 
  

   common 
  to 
  all, 
  may 
  owe 
  their 
  origin 
  to 
  the 
  basalt 
  itself, 
  from 
  which 
  they 
  

   may 
  have 
  been 
  emitted 
  iu 
  the 
  form 
  of 
  vapour. 
  

  

  Although 
  silica, 
  alumina, 
  and 
  lime 
  are 
  regarded, 
  and 
  justly 
  so, 
  as 
  being 
  

   little 
  affected 
  by 
  exposure 
  even 
  to 
  a 
  very 
  intense 
  heat, 
  I 
  am 
  neverthe- 
  

   less 
  disposed 
  to 
  believe 
  that 
  all 
  three 
  are 
  susceptible 
  of 
  being 
  evaporated 
  

   at 
  temperatures 
  not 
  unfrequently 
  used 
  in 
  the 
  arts. 
  From 
  iron 
  blast- 
  

   furnaces, 
  and 
  particularly 
  from 
  those 
  in 
  the 
  North 
  of 
  England, 
  a 
  vast 
  

   quantity 
  of 
  white 
  fume 
  or 
  smoke 
  is 
  emitted, 
  which 
  readily 
  condenses 
  

   on 
  a 
  cold 
  surface. 
  To 
  one 
  of 
  these 
  furnaces 
  in 
  the 
  county 
  of 
  Durham 
  

   I 
  attached 
  an 
  air-pump 
  worked 
  by 
  steam, 
  and 
  by 
  its 
  means 
  the 
  whole 
  of 
  

   this 
  fume 
  from 
  a 
  given 
  volume 
  of 
  gas, 
  as 
  it 
  escaped 
  from 
  the 
  furnace, 
  

  

  was 
  condensed 
  in 
  water. 
  

  

  On 
  analysis 
  it 
  was 
  found 
  to 
  be 
  composed 
  of 
  — 
  

  

  Silica 
  14-06 
  

  

  Alumina 
  and 
  some 
  peroxide 
  of 
  iron 
  25*70 
  

  

  Lime 
  . 
  2-30 
  

  

  Magnesia 
  trace 
  

  

  Chlorine 
  *61 
  

  

  Sulphuric 
  acid 
  *64 
  

  

  Oxide 
  of 
  zinc 
  19-99 
  

  

  Carbonates 
  of 
  potash 
  and 
  soda 
  .... 
  29-05 
  

  

  Carbonic 
  acid 
  7-83 
  

  

  100-18 
  

  

  Not 
  being 
  prepared 
  to 
  find 
  certain 
  of 
  these 
  bodies 
  carried 
  away 
  in 
  the 
  

   vaporous 
  form, 
  the 
  idea 
  suggested 
  itself 
  that 
  they 
  might, 
  in 
  the 
  first 
  in- 
  

   stance, 
  be 
  deoxidized 
  in 
  the 
  powerfully 
  reducing 
  atmosphere 
  of 
  the 
  

   hearth 
  of 
  the 
  furnace, 
  and 
  subsequently 
  reoxidized 
  in 
  its 
  upper 
  regions. 
  

   To 
  satisfy 
  myself 
  on 
  this 
  point, 
  I 
  drew 
  a 
  considerable 
  volume 
  of 
  the 
  gases 
  

   as 
  they 
  exist 
  in 
  the 
  hottest 
  portion 
  of 
  the 
  reducing 
  zone 
  and 
  passed 
  it 
  

   through 
  cold 
  mercury. 
  Had 
  any 
  such 
  action 
  as 
  that 
  indicated 
  been 
  

   effected, 
  I 
  would 
  expect 
  to 
  find 
  potassium 
  or 
  sodium 
  in 
  the 
  mercury. 
  

   No 
  trace, 
  however, 
  of 
  these 
  metals 
  was 
  detected, 
  and 
  I 
  therefore 
  con- 
  

   cluded 
  that 
  the 
  furnace-vapours 
  in 
  question 
  must 
  be 
  regarded 
  as 
  true 
  

   sublimates. 
  If 
  so, 
  and 
  if 
  the 
  estimate 
  of 
  the 
  quantity 
  be 
  correct, 
  many 
  

   thousands 
  of 
  tons 
  of 
  alumina 
  &c. 
  are 
  annually 
  evaporated 
  on 
  the 
  banks 
  

   of 
  the 
  Tees 
  duriug 
  the 
  process 
  of 
  smeltiug 
  iron. 
  

  

  If 
  similar 
  vapours 
  were 
  emitted 
  by 
  basalt 
  when 
  intensely 
  heated, 
  it 
  

   is 
  almost 
  certain 
  that, 
  under 
  the 
  great 
  pressure- 
  then 
  prevailing 
  at 
  the 
  

   depth 
  of 
  this 
  particular 
  bed, 
  some 
  portion 
  would 
  find 
  its 
  way 
  into 
  the 
  

   adjoining 
  strata. 
  Lying 
  above 
  the 
  basalt 
  is 
  some 
  8 
  or 
  9 
  feet 
  of 
  a 
  rock 
  

   spoken 
  of 
  as 
  " 
  white 
  post." 
  On 
  referring 
  to 
  the 
  analysis 
  formerly 
  quoted, 
  

   it 
  will 
  be 
  seen 
  that 
  this 
  bed 
  contains 
  88*25 
  per 
  cent, 
  of 
  silica 
  (it 
  is 
  there- 
  

  

  