420 
Varieties. 
f  Am.  Jour.  Pharm. 
t    Sept.  1, 1871. 
A  New  Experiment. — The  action  of  dilute  sulphuric  acid  oa  starch  is  very 
neatly  illustrated  in  a  new  experiment  suggested  by  A.  Yogel.  It  is  well 
known  that  writing  paper  is  so  largely  sized  with  starch  that  an  iodine  solution 
applied  upon  its  surface  will  produce  a  blue  color.  Vogel  traces  first  upon 
the  paper  some  writing  or  figures  with  dilute  sulphuric  acid.  The  paper  is 
then  gently  heated,  but  not  sufficiently  to  char  it.  If  now  the  iodine  solution 
is  applied,  portions  of  the  paper  treated  with  the  acid  remain  white,  while  the 
rest  is  blued.  The  same  paper  will  serve  repeatedly  for  the  experiment,  for 
the  blue  color  gradually  disappears. — Journ.  Frankl.  Inst.,  August,  1871. 
Decoration  of  Metals. — Dr.  Puscher  recommends  a  solution  composed  of  a 
mixture  of  3  parts  of  hyposulphite  of  soda  and  1  of  acetate  of  lead,  for  the  pur- 
pose of  decorating  metallic  surfaces.  When  heated  to  about  100^  0.,  this 
solution  deposits  a  layer  of  sulphide  of  lead  upon  any  metallic  surface  in  con- 
tact with  it — the  effect  of  the  peculiar  color  of  the  metal  beneath  being  to  pro- 
duce a  great  variety  of  tint. — Journ.  Frankl,  Inst.,  August,  1871. 
Gun-Cotton  \&  now  manufactured  in  England  to  an  amount  exceeding  100 
tons  per  annum.  The  cotton  fibre  is  reduced  to  a  pulp,  as  in  paper  making 
in  which  condition  the  excess  of  acids  is  readily  removed.  The  pulp  is  com- 
pressed into  disks,  under  a  pressure  of  18  tons  to  the  inch,  and  then  dried. 
These  disks  are  |  inch  to  7  inches  in  diameter,  and  ^  inch  to  2  inches  thick.  In 
the  open  air  this  compressed  cotton  burns  intensely,  but  without  explosion  ;  but 
when  properly  exploded  under  close  confinement,  its  strength  is  from  2  to  5 
times  that  of  the  same  weight  of  gunpowder.  If  accidentally  wetted,  this  form 
of  gun-cotton  can  be  re-dried  by  exposure  to  the  sun,  or  even  by  a  gentle  heat, 
without  risk  of  explosion  or  deterioration. — Journ.  Frankl.  Inst.,  August,  1871. 
Origin  of  Hail. — Prof.  Reinsch*  announces  that  it  is  impossible,  in  the  pres- 
ent state  of  onr  knowledge,  to  proclaim  a  theory  which  shall  satisfactorily  ex- 
plain the  origin  of  this  meteorological  phenomenon. 
Though  it  maybe  safely  asserted  that  the  conditions  originating  it  are  differ- 
ent from  those  producing  the  deposition  of  rain  or  snow,  or  that  these  condi- 
tions are  more  intense  in  character,  yet  a  microscopic  examination  of  hail  proves 
that  the  conditions  originating  it  are  by  no  means  always  the  same  ;  for  the 
structure  of  the  product  is  rarely  the  same.  He  mentions  the  curious  fact  that 
in  some  hail  which  he  examined  beneath  the  microscope,  there  was  found  at  the 
centre  of  the  stones  a  spherical  globule,  which  proved  to  be  air.  When  these 
globules  were  nearly  freed  by  the  melting  of  their  icy  confinements,  they  burst 
the  last  portions  of  the  shell  with  energy,  and,  expanding,  occupied  in  a  bubble 
form  a  space  more  than  fifty  times  greater  than  when  confined  ;  showing  that 
they  had  been  subject  to  a  pressure  equivalent  to  more  than  fifty  atmospheres. 
*Pogg.  Ann.,  CCXVIII,  623. 
