386 
RESEARCHES  ON  BLACK  PHOSPHORUS. 
sists.  I  also  found  that  to  insure  success  in  bleaching  phospho- 
rus by  repeated  distillations,  it  is  necessary  between  each  opera- 
tion to  submit  it  to  insolation  in  glass  tubes,  so  as  to  convert  the 
yellow  part  which  is  volatile  into  red  phosphorus,  which  is  fixed. 
When  bleached  in  this  way  phosphorus  has  a  strong  tendency  to 
turn  suddenly  black.  Rapid  cooling  may  produce  this  effect,  as 
Thenard  has  shown  ;  he  obtained  this  result  by  melting  his  phos- 
phorus in  fine  tubes,  which  he  then  plunged  into  cold  water. 
Melted  again,  the  black  phosphorus  thus  produced  lost  its  color, 
and  did  not  regain  it  till  it  had  been  rapidly  cooled.  Hence  it 
has  been  inferred  that  black  phosphorus  is  the  result  of  a  kind  of 
tempering.  This  is  an  error,  for  I  have  obtained  it  more  easily 
in  quite  a  contrary  way — that  is  to  say,  by  very  gradual  cooling. 
In  this  way  I  habitually  procure  black  phosphorus.  For  this 
purpose  I  distil  phosphorus,  previously  insolated,  until  the  pro- 
duct collected  in  the  balloon  very  slowly  cooled  in  the  water-bath 
suddenly  turns  black.  This  curious  change  generally  takes  place 
in  the  following  manner : — When  the  temperature  has  fallen  to 
about  44°,  the  phosphorus  solidifies  in  the  usual  way  into  a  white 
mass;  then,  when  after  several  hours  the  water  is  only  at  5°  or 
6°,  the  phosphorus  suddenly — in  the  space  of  a  second — turns  to 
a  beautiful  black.  Black  phosphorus,  when  once  obtained,  may 
be  re-melted  and  re-distilled  without  fear.  When  liquid  it  is 
colorless,  but  returns  to  black  by  very  slow  cooling.  It  presents, 
moreover,  all  the  characteristic  properties  of  ordinary  phosphorus, 
except  that  it  is  softer. 
It  follows  from  the  above  researches  that  as  yellow  phosphorus 
is  recognized  as  impure,  and  as  the  white  is  but  a  transitory  state 
before  arriving  at  the  black,  the  latter,  much  more  stable,  should 
be  considered  not  as  an  anomaly,  but,  on  the  contrary,  as  the 
true  type.  A  support  for  this  opinion  is  to  be  found  in  the  fact 
that  phosphorus  which  has  been  long  exposed  to  diffused  light, 
and  has  become  covered  with  a  layer  of  red,  is  found  to  be  black 
inside,  as  though,  in  becoming  spontaneously  purified,  it  had  un- 
dergone a  molecular  change  somewhat  analogous  to  crystallisa- 
tion.— London  Chem.  Neivs^  June  16,  1865,  from  Oomptes  Ren- 
du*, lx.  830. 
