ME.  G.  GOEE  ON  THE  PEOPEETIES  OF  ELECTEO-DEPOSITED  ANTIMONY.  193 
40.  The  peculiar  change  is  attended  by  alterations  in  the  colour  and  fracture  of  the 
metal ; from  a bright  steel  colour  and  glassy  fracture,  it  passes  to  a dull  grey  colour  and 
granular  fracture,  as  if  it  progressed  a stage  towards  the  crystalline  modification : this  is 
particularly  manifest  in  thick  pieces  gradually  heated  in  the  air  until  the  change  occurs. 
It  is  also  attended  by  a change  in  the  form  of  the  metal ; bars  which  were  nearly  straight 
before  the  action,  were  considerably  curved  afterwards,  and  the  direction  of  the  curva- 
ture was  such,  that  the  outer  side,  or  that  last  deposited,  invariably  became  more  con- 
cave. Upon  applying  heat  to  a thin  layer  of  dark  antimony,  formed  upon  a thin  sheet 
of  silver,  it  immediately  underwent  the  change,  and  became  exceedingly  curved  in  a 
similar  direction.  This  direction  of  curvature  appears  to  be  due  to  a cause  already 
mentioned  (see  16.  17),  the  unequal  cohesion  of  the  inner  and  outer  surfaces  of  the 
metal. 
41.  By  appljlng  heat  to  the  ends  of  deposits  formed  upon  heliacal  copper  wires, 
the  action  was  gradually  propagated  to  the  opposite  ends  at  a speed  varying  from  12  to 
30  feet  per  minute ; and  its  rapidity  of  progress  appeared  to  be  dependent  upon  the  tem- 
perature of  the  metal  and  the  cooling  influence  of  the  enclosed  wire,  also  upon  the 
absence  of  grey  nodules ; the  warmer  the  antimony,  the  greater  its  thickness,  and  the 
more  free  it  was  from  grey  metal,  the  more  rapid  was  the  action ; and  in  cases  Avhere  the 
deposit  was  thin  in  places,  or  had  occasional  grey  nodules,  the  action  was  impeded  at 
those  parts,  and  sometimes  totally  arrested.  Grey  nodules  invariably  impeded  the 
action,  and  caused  it  to  progress  by  sudden  starts.  The  progress  of  the  change  was 
rendered  more  or  less  visible  by  the  evolution  of  a cloud  of  vapour  at  its  advancing 
point ; also  in  the  case  of  fine  copper  wires,  by  a peculiar  snake-like  movement  in  the 
coils  at  that  part,  apparently  produced  by  the  cohesive  alteration  already  mentioned 
(see  16.  17.  40.).  After  the  change,  the  layer  of  antimony  contained  numerous  trans- 
verse and  longitudinal  fissures,  as  if  it  had  contracted  in  those  directions. 
42.  In  a number  of  instances,  by  connecting  the  ends  of  the  copper  wires  with  a gal- 
vanometer, and  inducing  the  change  in  the  coating  by  a heated  wire,  a feeble  electric 
cuiTent  occurred  in  the  enclosed  wire  whenever,  from  thinness  of  the  coating,  its  termi- 
nation, or  other  causes,  the  action  ceased ; and  in  every  case  passed  in  a direction  oppo- 
site to  that  of  the  peculiar  action.  By  touching  the  deposit  with  a heated  wire  some 
time  afterwards  at  the  point  where  the  action  ceased,  a current  of  ordinary  thermo- 
electricity was  in  each  case  generated,  and  passed  in  a similar  direction. 
43.  By  exciting  the  peculiar  change  in  two  pieces,  weighing  upwards  of  600  grains 
each,  placed  in  the  Ucinity  of  the  poles  of  delicately  suspended  magnetic  needles,  no 
deflection  of  the  latter  in  either  case  occurred. 
44.  By  taking  two  bars,  each  about  3 inches  long,  one  of  amorphous  antimony  and 
one  of  the  crystalline  variety,  connecting  their  extremities  with  a galvanometer,  and 
cautiously  bringing  a small  flame  of  a spirit-lamp  within  half  an  inch  of  their  remote  and 
touching  ends,  the  dark  bar  was  found  to  be  feebly  thermo-electro-positive  to  the  grey 
one.  A thin  rod  of  changed  antimony  was  found,  in  a second  experiment,  to  be  weakly 
MDCCCLVIII.  2 D 
