240 
Liquid  Carbonic  Acid  Gas. 
Am..  Jour.  Pharmu 
May,  1901.. 
opening,  at  the  bottom  this  bore  terminates  in  a  small  piece  of  pipe 
closed  at  the  bottom  and  having  numerous  very  minute  perfora- 
tions. The  valve  by  which  the  tube  is  opened  or  closed  is  a  long 
piece  of  metal,  terminating  in  a  needle-like  point,  which,  when 
screwed  down  on  the  valve  seat,  closes  the  opening  just  below 
where  the  side  bore  issues  out.  In  this  arrangement  lies  the  whole 
secret  of  the  liquefaction  of  the  gas.  The  gas  is  let  into  the  tank 
through  the  side  opening  at  a  pressure  of  540  pounds,  it  escapes 
inside  through  the  minute  openings  at  the  bottom  of  the  bore  in 
the  form  of  a  fine  spray,  and  by  this  sudden  expansion  lowers  the 
temperature  so  greatly  and  rapidly  that  the  incoming  gas  is  at  once 
liquefied  and  trickles  down  the  sides  of  the  tank.  The  process  is  a 
continuous  one,  the  compressed  gas  being  supplied  until  the  tube 
is  full,  shown  by  the  reading  of  the  pressure  gauge  outside  being 
the  same  as  at  the  last  compressor,  540  pounds,  for  as  fast  as  the 
gas  is  permitted  to  flow  into  the  tube  and  escape  through  the  per- 
forated  bit  of  pipe  it  liquefies  itself,  the  compression  being  of  course 
kept  up  at  the  initial  degree.  During  this  process  the  tubes  are 
surrounded  by  a  freezing  mixture  to  aid  in  the  condensation  of  the 
gas  by  absorbing  any  heat  from  compression  in  the  supply  pipes. 
In  some  factories,  the  tanks,  tubes  or  cylinders,  all  names  for  the 
container  of  the  liquid  gas,  are  partially  exhausted  of  air  before  fill- 
ing; in  others  the  air  is  left  in,  of  course  making  a  slight  difference 
in  the  amount  of  liquid  gas  the  tube  can  hold.  Another  important 
point  to  the  druggist  is  the  dryness  of  his  liquid  gas ;  very  often, 
especially  where  the  liquid  gas  is  sold  at  a  low  figure,  the  gas  is 
not  dried  before  compression,  and  there  is  often  a  quart  or  more  of 
water  found  in  every  tube  filled  with  wet  gas.  This  freezes  as  soon 
as  the  gas  begins  to  be  drawn  off  and  sometimes  creates  a  great 
deal  of  trouble  by  collecting  in  the  exhaust  pipe  in  the  form  of 
solid  ice,  or  fine  crystals,  and  blocking  up  the  outlet;  hence  the 
druggist  should  insist  upon  receiving  only  liquid  gas  that  has  been 
well  dried  before  it  is  liquefied,  to  save  annoyance  and  loss  in  pay- 
ing for  a  pound  or  two  of  water  and  ice  at  the  price  of  liquid  gas. 
The  ordinary  size  of  tanks  contains  from  twenty  to  twenty-two 
pounds  of  liquid  C02,  but  there  are  other  sizes  that  contain  almost 
double  the  amount.  The  old  style  tank  was  made  of  cast  steel  and 
could  susta  11  a  pressure  of  3700  pounds  to  the  square  inch;  the 
newer  tanks  are  made  of  a  mild  steel  that  can  stand  a  pressure  of 
