Am.  Jour.  Pharm.  1 
Aug.  1, 1872.  J 
Varieties. 
377 
at  each  end.  This  forms  the  main  peculiarity  of  the  arrangement.  When  air 
is  forced  into  the  bottle  by  the  blower  in  jerks,  it  finds  a  difficulty  in  escaping 
as  fast  as  it  comes  in,  on  account  of  the  six  fine  openings  in  the  glass  tubes 
that  it  has  to  pass  through  on  its  way  from  the  bottle  to  the  nozzle,  and  it  thus 
acquires  a  certain  pressure  in  the  bottle  and  flows  out  toward  the  nozzle  as  a 
regular  blast.  The  bottle  may  be  about  6  inches  high  by  3^  inches  wide,  with 
a  neck  1^  inch  diameter  ;  but  of  course  the  dimensions  are  of  no  great  impor- 
tance. On  the  whole,  a  somewhat  large  bottle  is  better  than  a  small  one.  The 
pieces  of  glass  tubing  we  use  are  2  inches  long  by  £  inch  in  diameter.  The 
apparatus  will  be  stronger  if,  instead  of  a  glass  bottle,  a  tin  cylinder  is  used, 
about  4  inches  high  by  2  inches  in  diameter,  with  two  tin  tubes  opening  into  its 
top.  Small  metal  cylinders,  with  a  fine  hole  at  each  end,  may  be  used 
instead  of  the  little  glass  tubes.  A  blowing  apparatus  constructed  in  this 
manner  will  deliver  a  perfectly  regular  blast,  and  will  be  of  practical  interest 
to  those  who  are  thinking  of  working  in  places  where  it  is  difficult  or  impos- 
sible to  repair  the  ordinary  instruments. — Scientific  American,  July  6,  1872. 
On  the  light  emitted  by  the  vapor  of  iodine. —  Salet  has  found  that  the  vapor 
of  iodine  may  be  heated  to  redness  like  a  solid  or  liquid.  It  then  emits  the 
less  refrangible  luminous  rays  which  furnish  a  continuous  spectrum.  The  ex- 
periment is  easily  made  by  heating  the  iodine  in  a  tube  of  Bohemian  glass.  A 
small  crystal  of  iodine  is  placed  in  a  tube  of  thick  glass,  which  is  then  heated 
strongly  at  some  distance  from  the  crystal.  When  the  glass  is  red  for  a  con- 
siderable part  of  its  length,  it  is  to  be  allowed  to  cool  until  it  is  no  longer  visi- 
ble in  the  dark  ;  the  iodine  is  then  to  be  rapidly  volatilized.  The  colored  vapor 
reaching  the  heated  part  of  the  tube  then  glows  with  a  distinct  red  light.  This 
experiment  shows  that  the  iodine  becomes  luminous  at  a  lower  temperature 
than  glass.  Another  method  of  exhibiting  the  incandescence  of  the  vapor  of 
iodine  is  the  following  :  A  spiral  of  fine  platinum  wire  is  sealed  in  the  interior 
of  a  tube  of  glass  eight  millimetres  in  diameter.  Pure  iodine  is  then  intro- 
duced into  the  tube,  which  after  expulsion  of  the  air  is  sealed.  If  the  iodine 
be  then  volatilized  and  the  wire  ignited  by  a  battery,  the  spiral  appears  sur- 
rounded by  a  flame  of  a  very  rich  red  color,  which  yields  the  well-known  inter- 
rupted spectrum. — Am.  Jour,  of  Science  and  Arts,  July,  1871,  from  Compter 
Rendus,  Tome  lxxiv,  p.  1249. 
Photo -engraving  on  Metals  —  Pi.  recent  process  for  producing  engraved  sur- 
faces in  metal  by  photography  is  described  as  follows  :  A  pure  silver  (or  alloy) 
surface  is  first  taken,  and  after  finely  polishing  or  frosting  it  is  exposed  to  the 
action  of  iodine,  and  a  film  of  iodide  of  silver  thus  obtained.  The  plate  is  then 
exposed  to  the  action  of  light,  in  the  camera  or  under  a  photographic  nega- 
tive, until  a  faint  image  is  obtained.  It  is  then  submitted  to  the  action  of  an 
electrotype  battery  (copper  solution)  when  a  well  defined  image  of  the  object 
is  obtained  in  copper  (the  copper  only  attaches  itself  to  those  portions  of  the 
plate  which  have  been  rendered  conductors  of  electricity  by  the  action  of  the 
light).    The  plate  is  next  dried  and  etching  solution  poured  over  it,  composed 
