MaJch!^9^2o:}      De-Arsenication  of  Sulphuric  Acid.  179 
But  there  are  one  or  two  features  in  the  biblical  description  of  manna 
that  call  for  comment.  One  is  the  reason  why  it  kept  over  the  Sab- 
bath without  becoming  filled  with  worms  and  stinking.  The  di- 
rections given  to  bake  or  seethe  it  would  naturally  kill  all  insect  life 
in  it;  and  the  manna,  that  was  to  be  preserved  for  generations  as 
evidence  of  the  Israelites  being  miraculously  fed,  was  probably 
baked,  and  may  have  become  hard  or  horny  in  the  process.  It  is  not 
easy  to  explain  otherwise  why  they  "ground  it  in  mills  or  beat  it  in 
mortars,"  especially  as  in  the  fresh  state  it  was  soft  enough  to  melt 
in  the  sun's  heat.  The  text  is  difficult  to  follow,  but  in  Numbers 
xi,  8,  it  seems  to  imply  that,  after  grinding  it,  it  was  seethed  and  made 
into  cakes. 
The  fact  that  the  manna  was  abundant  enough  to  feed  a  multi- 
tude of  people  for  forty  years  indicates  that  by  some  unrecognized 
means  the  plant  miraculously  increased,  and  the  conditions  were 
those  of  uncultivated  land,  since  it  ceased  when  they  "came  to  land 
inhabitated, "  "in  the  borders  of  the  land  of  Canaan." 
Another  point  is  the  continuous  production  of  the  plant  for  forty 
years  and  all  the  year  around.  But  we  have  the  evidence  at  home 
that  the  mushroom,  which  in  the  wild  state  is  usually  confined  to 
August  and  September,  can  be  produced  all  the  year  round  if  the 
natural  conditions  of  heat,  moisture  and  food  are  artificially  provided. 
There  may  have  been  conditions  connected  with  the  manner  of  life 
of  the  people  which  produced  artificially  the  requirements  of  the 
plant.  At  all  events,  the  study  of  the  life-history  of  the  manna  plant 
in  the  future  offers  many  interesting  problems  to  the  research  work- 
ers at  Khartoum,  or  elsewhere,  if  the  plant  can  be  obtained  and 
cultivated. 
NOTE  ON  THE  DE-ARSENICATION  OF  SULPHURIC  ACID 
BY  HYDROGEN  SULPHIDE.* 
By  T.  S.  Moorb. 
According  to  the  published  information,  the  strength  of  sulphuric 
acid  submitted  to  de-arsenication  by  hydrogen  sulphide  must  not 
exceed  110°  Tw.  (64.26  per  cent.  H2SO4),  and  in  many  works  much 
less  than  this,  down  to  100°  Tw.  (59.7  per  cent.  H2SO4).    The  ex~ 
*  From  Jour.  Soc.  Chem.  Ind.,  December  15,  1919. 
