340 
ON  BORON. 
forms.  Boron  alone,  placed  between  carbon  and  silicium,  both 
of  which  crystallize  most  perfectly,  formed  an  exception  to  this 
rule.  Investigations  upon  this  substance,  commenced  by  the 
authors  separately  but  completed  in  common,  have  put  an  end 
to  this  exception,  by  showing  that  boron  exists  in  three  distinct 
states,  thus  presenting  the  same  analogies  as  silicium  to  carbon, 
but  in  a  still  more  marked  degree.* 
1.  Crystallized  Boron,  or  Diamond  of  Boron  This  substance 
was  obtained  in  the  form  of  transparent  crystals,  sometimes  of  a 
garnet-red  and  sometimes  of  a  honey-yellow  color,  although  the 
color  could  not  be  regarded  as  specific,  for,  like  that  of  precious 
stones,  it  might  be  due  to  exceedingly  small  and  variable  quan- 
tities of  foreign  matters,  especially  silicium,  carbon,  or  even 
amorphous  boron.  It  is  therefore  to  be  hoped  that  crystallized 
boron  may  be  obtained  colorless. 
The  crystals  possess  such  brilliancy  and  refractive  power  as 
to  be  only  comparable  to  the  diamond.  This  extreme  refractive 
power  is  the  cause  of  the  metallic  aspect  of  crystals  of  too  large 
a  size  to  be  traversed  by  light.  Probably,  if  boron  should  be 
obtained  in  large  colorless  crystals,  it  would  present  exactly  the 
aspect  of  the  diamond. 
Another  very  important  analogy  is  its  hardness.  Boron 
scratches  corundum  with  the  greatest  ease,  so  that  a  cut  sapphire, 
submitted  to  the  action  of  the  powder  of  boron,  very  rapidly  lost 
its  angles.  A  cut  diamond,  with  which  the  crystals  of  boron 
were  crushed  upon  a  surface  of  polished  quartz,  was  slightly 
attacked  at  all  the  points  of  contact.  Boron  must  therefore  be 
regarded  as  the  hardest  of  all  known  bodies,  or  at  all  events  next 
to  the  diamond. 
The  crystalline  form  of  boron  has  still  to  be  ascertained,  The 
authors  have  frequently  obtained  pretty  large  crystals  of  boron  ; 
but  on  closely  examining  these,  they  proved  to  be  very  compli- 
cated macles,  produced  by  the  regular  aggregation  of  a  great 
number  of  very  small  elementary  crystals.  From  their  behaviour 
towards  polarized  light,  the  crystals  do  not  appear  to  belong  to 
the  regular  system. 
*  The  boron  analogous  to  ordinary  carbon  was  discovered  by  Gay-Lussac 
and  Thenard,  by  the  reaction  of  potassium  upon  boracic  acid. 
