266  Methods  of  Gas  Warfare.         {AmAprii/  I£s.m' 
and  are  still  in  course  of  development.  The  enemy  started  using 
them  soon  after  the  first  cloud  attack.  He  began  with  the  cele- 
brated "tear"  shells.  A  concentration  of  one  part  in  a  million  of 
some  of.  these  lachrymators  makes  the  eyes  water  severely.  The 
original  tear  shells  contained  almost  pure  xylyl  bromide  or  benzyl 
bromide,  made  by  brominating  the  higher  fractions  of  coal-tar  dis- 
tillates. 
The  German  did  his  bromination  rather  badly.  As  you  know, 
it  should  be  done  very  carefully  or  much  dibromide  is  produced, 
which  is  solid  and  inactive.  Some  of  the  shells  contained  as  much 
as  twenty  per  cent,  dibromide,  enough  to  make  the  liquid  pasty  and 
inactive.  The  shells  used  contain  a  lead  lining,  and  have  a  parti- 
tion across  the  shoulder,  above  which  comes  the  T.  N.  T.  and  the 
fuse.  These  shells  had  little  effect  on  the  British,  but  one  attack 
on  the  French,  accompanied  by  a  very  heavy  bombardment  with 
tear  shells,  put  them  out  badly.  The  eyes  of  the  men  were  affected, 
and  many  of  the  men  were  even  anesthetized  by  the  gas,  and  were 
taken  prisoner. 
Our  first  big  experience  was  an  attack  at  Vermelles.  The  Ger- 
mans put  down  a  heavy  barrage  of  these  shells  and  made  an  infantry 
attack.  The  concentration  was  great,  the  gas  went  through  the 
helmets,  and  the  men  even  vomited  inside  their  helmets.  But  it  is 
dimcult  to  put  down  a  gas  barrage,  and  there  is  danger  that  it  will 
not  be  a  technical  success.  In  the  instance  cited  certain  roads  were 
not  cut  off  sufficiently,  so  that  reinforcements  got  up.  This  attack, 
however,  opened  our  eyes  to  the  fact  that,  as  in  the  case  of  gas 
clouds,  concentration  would  be  developed  so  as  to  make  it  high 
enough  to  produce  the  required  effect  under  any  circumstances. 
When  the  Germans  started  using  highly  poisonous  shells,  which 
was  at  the  Somme  in  191 6,  they  did  not  attend  to  this  sufficiently, 
although  enormous  numbers  of  shell  were  used.  The  substance 
used  was  trichloromethyl-chloroformate,  but  not  in  great  strength. 
It  had  no  decided  reaction  on  the  eyes,  hence  the  men  were  often 
caught. 
The  quantity  of  gas  that  can  be  sent  over  in  shells  is  small. 
The  average  weight  in  a  shell  is  not  more  than  six  pounds,  whereas 
the  German  gas  cylinders  contain  forty  pounds  of  gas.  To  put  over 
the  same  amount  of  gas  as  with  gas  clouds,  say  in  five  minutes  per 
thousand  yards  of  front,  would  require  a  prohibitive  number  of 
guns  and  shells.    It  becomes  necessary  to  put  the  shells  on  definite 
