360 
ON  AFKICAN  SENNA. 
On  pouring,  however,  the  acid  on  the  phosphorus,  I  observed 
an  immediate  sense  of  warmth,  and  I  had  only  just  time  to  trans- 
fer the  mixture  to  a  large  jug,  and  carry  it  into  the  open  air, 
before  very  rapid  chemical  action  commenced,  with  evolution  of 
red  nitrous  fumes. 
When  the  reaction  had  almost  ceased,  the  mixture  was  trans- 
ferred to  a  basin,  and  a  gentle  heat  applied  until  'the  nitric  acid 
was  exhausted,  and  a  syrupy  acid  obtained. 
When  tested  with  nitrate  of  silver,  it  revealed  abundance  of 
phosphorous  acid  ;  which  was  oxydized  to  (P05)  by  the  addition 
of  nitric  acid  equal  to  about  one-third  of  the  quantity  originally 
taken. 
This  large  loss  may  be  in  part  prevented  by  using  the  nitric 
acid  diluted  by  three  instead  of  two  parts  of  water.  The  action 
then  proceeds  quietly,  and  no  red  vapors  are  eliminated.  The 
action  nearly  ceases  when  about  half  the  phosphorus  is  dissolved. 
(The  solution  then  contains,  besides  (P05)  and  P03),  what  I 
believe  to  be  (PO)  hypophosphorous  acid,  the  presence  of  which 
is  indicated  by  a  white  precipitate  with  nitrate  of  silver,  passing 
into  black  on  the  application  of  heat.)  It  is  finished  by  the 
application  of  heat,  and  the  addition  of  one-fourth  the  original 
quantity  of  nitric  acid,  or  sufficient  to  raise  all  the  oxides  to 
fP05).  I  think  this  extra  expense  of  nitric  acid  is  amply  com- 
pensated for  by  the  absence  of  personal  danger,  and  the  saving 
in  glass  retorts  and  condensers,  whose  occasional  fracture  cannot 
be  avoided  in  the  old  process. 
Hoping  these  remarks  may  prove  useful  to  my  brethren, 
I  am,  Sir,  your  obedient  servant, 
Thomas  B.  Gkoves,  F.C.S. 
Weymouth,  March  18th,  1858. 
AFKICAN  SENNA. 
Mr.  Bentley  exhibited  to  the  meeting  a  sample  of  senna  from 
Africa,  which  had  been  given  to  him  by  Dr.  Livingstone,  the 
celebrated  African  traveller.  He  thought  that  such  a  specimen 
was,  at  the  present  time,  of  much  interest,  as  an  expedition  was 
about  to  start  for  the  exploration  of  the  Zambesi  river,  with  a 
view  of  ascertaining  the  nature  of  the  vegetable  and  mineral 
