6i6 
Amorphous  Boron. 
Am.  Jour.  Pharm. 
Dec,  1892. 
AMORPHOUS  BORON.1 
By  H.  Moissan. 
A  summary  of  the  properties  of  pure  amorphous  boron.  Boric 
acid  is  twice  treated  with  less  than  the  theoretical  quantity  of  mag- 
nesium powder,  and  the  product,  on  treatment  with  an  acid,  leaves 
amorphous  boron. 
Amorphous  boron  is  a  bright,  maroon-colored  powder  which 
stains  the  ringers  and  can  be  compressed  into  a  cake.  Its  sp.  gr.  is 
2-45.  It  does  not  fuse  at  the  temperature  of  the  electric  arc,  but 
shrinks  slightly  and  increases  in  density  when  heated  to  1,500°  in  an 
atmosphere  of  hydrogen.  Its  electrical  conductivity  is  very  low,  the 
specific  resistance  being  801  megohms. 
Boron  takes  fire  in  the  air  at  7000,  and  burns  in  oxygen  with  a 
brilliant  green  flame  having  little  actinic  power  ;  in  either  case  the 
combustion  is  soon  stopped  by  the  formation  of  a  layer  of  boric 
anhydride  on  the  surface  of  the  boron.  It  combines  energetically 
with  sulphur  at  6io°  to  form  a  sulphide  which  is  decomposed  by 
water  with  evolution  of  hydrogen  sulphide;  it  behaves  in  the  same 
way  with  selenium,  but  does  not  combine*  with  tellurium. 
Boron  burns  in  dry  chlorine  at  4100,  and  in  bromine  vapor  at 
7000,  with  the  formation  of  boron  chloride  and  bromide.  It  is 
dissolved  by  bromine  water,  and  more  readily  by  a  solution  of  bromine 
in  potassium  bromide  solution,  but  it  does  not  combine  with  iodine. 
It  combines  with  nitrogen  at  1,230°,  but  not  directly  with  phos- 
phorus, arsenic  or  antimony.  Neither  does  it  combine  directly  with 
carbon  or  silicon,  although  a  boron  carbide  is  formed  when  boron  is 
heated  in  the  electric  arc  in  an  atmosphere  of  hydrogen. 
The  alkali  metals  have  no  action  on  boron,  but  magnesium  com- 
bines with  it  at  a  red  heat.  Iron  and  aluminium  form  borides  only 
at  high  temperatures,  whilst  silver  and  platinum  combine  with  it 
quite  readily. 
Acids  react  energetically  with  boron  ;  sulphuric  acid  is  reduced  at 
250°  ;  the  action  of  nitric  acid  is  so  vigorous  as  to  raise  the  tempera- 
ture to  incandescence;  phosphoric  anhydride  is  reduced  to  phosphorus 
at  8oo°  ;  arsenious  and  arsenic  acids  are  reduced  to  arsenic  at  a  dull 
red  heat ;  iodic  acid  in  solution  is  reduced  to  iodine  in  the  cold,  and 
1  Compt.rend.,  114,  617-622;  Jour.  Chem.  Soc,  Octbr.,  1892,  p.  1153. 
