260 
Methods  of  Gas  Warfare. 
Am.  Jour.  Pharm. 
April,  19 18. 
Presumably  they  intended  to  win  the  war,  and  they  might  conceiva- 
bly have  won  it  then  and  there  if  they  had  foreseen  the  tremendous 
effect  of  the  attack.  It  is  certain  that  they  expected  no  immediate 
retaliation,  as  they  had  provided  no  protection  for  their  own  men. 
They  made  a  clear  and  unobstructed  gap  in  the  lines,  which  was  only 
closed  by  the  Canadians,  who  rallied  on  the  left  and  advanced,  in 
part  through  the  gas  cloud  itself. 
The  method  first  used  by  the  Germans,  and  retained  ever  since, 
is  fairly  simple,  but  requires  great  preparation  beforehand.  A  hole 
is  dug  in  the  bottom  of  the  trench  close  underneath  the  parapet, 
and  a  gas  cylinder  is  buried  in  the  hole.  It  is  an  ordinary  cylinder, 
like  that  used  for  oxygen  or  hydrogen.  It  is  then  covered  first  with 
a  quilt  of  moss,  containing  potassium  carbonate  solution,  and  then 
with  sand  bags.  When  the  attack  is  to  be  made  the  sand  bags  and 
protecting  cover  are  taken  off  the  cylinder,  and  each  cylinder  is  con- 
nected with  a  lead  pipe  which  is  bent  over  the  top  of  the  parapet. 
A  sand  bag  is  laid  on  the  nozzle  to  prevent  the  back  "  kick  "  of  the 
outrushing  gas  from  throwing  the  pipe  back  into  the  trench.  Our 
own  methods  are  practically  identical  with  those  first  used  by  the 
Germans. 
The  success  of  a  cloud  gas  attack  depends  on  thorough  prepara- 
tion beforehand.  The  attackers  must  know  the  country,  the  layout 
of  the  trenches,  and  the  direction  and  velocity  of  the  wind  with  cer- 
tainty. Favorable  conditions  are  limited  practically  to  wind  veloci- 
ties between  twelve  and  four  miles  an  hour.  A  wind  of  more  than 
twelve  miles  an  hour  disperses  the  gas  cloud  very  rapidly.  An  up- 
ward current  of  air  is  the  worst  foe  of  gas.  The  weight  of  the  gas 
is  not  an  important  factor  in  carrying  it  along,  for  it  mixes  rapidly 
with  air  to  form  the  moving  "  cloud."  The  time  occupied  by  a  gas 
attack  is  too  short  to  permit  of  much  diffusion  of  the  gas  out  of  the 
original  mixture. 
The  gas  attack  must  be  planned  very  carefully.  If  the  trench 
line  is  very  irregular  it  is  likely  that  gas  will  flow  into  a  portion  of 
one's  own  trenches.  The  limits  of  safety  in  wind  direction  are 
thus  determined  by  the  direction  of  the  lines  of  the  trenches.  The 
Germans  use  a  400  angle  of  safety ;  that  mean's  that  on  a  given 
straight  portion  of  the  front  the  wind  direction  must  lie  between 
the  two  directions  which  make  angles  of  400  with  the  neighboring 
sections  of  the  front.  The  most  suitable  type  of  country  is  where 
the  ground  slopes  gently  away  from  where  the  gas  is  being  dis- 
