238  Liquid  Carbonic  Acid  Gas.  {^'^;wFm' 
In  this  country  the  collection  of  gas  formed  by  fermentation  in 
the  process  of  brewing  has,  as  yet,  assumed  little  importance,  but 
when  the  use  of  liquid  carbon  dioxide  becomes  more  general  as  the 
motive  power  of  machinery  there  is  little  doubt  that  the  valuable 
by-product  now  being  wasted  will  be  carefully  collected  by  the 
brewers.1  The  same  wilful  waste  of  valuable  source  of  power  is 
also  notable  in  the  vast  coking  industry  of  this  State,  thousands  of 
tons  of  gas  going  to  absolute  waste  every  day  in  the  coke  fields, 
just  as  in  former  days  tar  was  considered  as  not  being  worth  collect- 
ing. But  when  the  use  of  liquid  gases  as  a  source  of  power  is  made 
practically  possible  by  improvements  in  liquid-gas  engines  we  may 
look  to  see  this  "  by-product  "  as  carefully  and  jealously  saved  as  is 
now  the  tar  from  gas  works.  Another  fact  to  be  borne  in  mind  is 
that  when  we  make  use  of  the  gas  from  combustion,  collected  and 
liquefied  from  the  stacks  of  our  factories'  countless  chimneys,  we 
add  to  the  amount  of  power  possible  from  coal  an  economy  of 
material  and  energy  of  incalculable  amount. 
At  the  present  time,  the  uses  of  liquid  carbon  dioxide  are  chiefly 
for  refrigerating  purposes  and  for  charging  soda  water,  so  there  is 
not  sufficient  demand  for  special  inventive  genius  as  yet;  indeed,  so 
limited  are  these  uses  and  so  keen  the  competition  that  were  it  not 
for  the  "by-products"  of  manufacture  it  is  possible  that  the  drug- 
gist would  not  yet  have  this  convenient  means  for  making  his  soda 
water.  The  value  of  these  by-products  is  what  makes  the  cost  of 
liquid  gas  so  small,  if  it  were  made  and  sold  simply  by  itself  the  cost 
would  be  many  times  greater  than  it  now  is.  As  chemistry  makes 
further  strides,  we  may  look  for  even  cheaper  gas,  as  more  and  more 
by-products  are  made  use  of,  the  most  likely  sources  being  the  gas 
from  the  burning  of  limestone  to  make  lime  and  the  collection  of  the 
gases  of  fermentation.  The  subject  of  these  by-products  is  too  large 
to  be  taken  up  in  this  short  paper,  being  almost  a  review  of  a  dozen 
different  industries  in  itself. 
By  whatever  process  it  be  made,  the  liquid  C02  intended  for 
charging  soda  water  must  be  purified  before  it  is  fit  for  use,  there 
usually  being  more  or  less  impurities  in  it  that  render  it  unsafe  in 
its  crude  state.    This  purification  is  also  of  importance  in  reducing 
1  Large  quantities  of  liquid  C02  are  now  imported  chiefly  from  Germany,  in 
tubes  holding  200  or  300  pounds.  This  is  collected  from  breweries  there  and 
liquefied  for  commercial  uses  and  exports. 
