222  Apparatus  for  Estimating  Urea.  {^™iviay'i87^^'"'' 
nombro  yo,  atendiendo  al  Canon  243,  de  su  Filosofia  Botanica  en  que 
dice,  Nomen  genericum  dignum  alio^  licet  aptiore^  permutare  non  licet. '''^^ 
"  Though  the  Canons  of  Linnaeus  may  no  longer  command  the  im- 
plicit obedience  that  they  were  once  thought  to  deserve,  it  cannot  be 
denied  that  there  is  a  general  reluctance  among  botanists  to  alter  the 
Linnean  names,  and  this  is  particularly  the  case  in  the  present  instance, 
where  the  alteration  advocated  would  require  to  be  followed  in  innum- 
erable writings  on  pharmacy  and  chemistry.  '  In  our  science,'  wrote 
Dr.  J.  E.  Smith,  in  1807  ('  Introduction  to  Botany'),  'the  names  estab- 
lished throughout  the  works  of  Linnaeus  are  become  current  coin,  nor 
can  they  be  altered  without  great  inconvenience.  Perhaps,  if  he  had 
foreseen  the  future  authority  and  popularity  of  his  writings,  he  might 
himself  have  improved  upon  many  which  he  adopted  out  of  deference 
to  his  predecessors,  and  it  is  in  some  cases  to  be  regretted  that  he  has 
not  sufficiently  done  so." 
ON  A  SIMPLE  APPARATUS  FOR  ESTIMATING  UREA. 
BY  RICHARD  APJOHN,  F.  C.  S. 
Proelector  of  Chemistry  in  Gonville  and  Caius  College,  Cambridge. 
A  rapid  and  accurate  process  for  estimating  urea  is  of  so  much  im- 
portance in  a  medical  point  of  view,  that  the  recent  memoir  of  Russell 
and  West  on  the  subject  (see  ''Journal  of  the  Chemical  Society,"  Au- 
gust, 1874)  has  necessarily  attracted  much  attention.  The  principle  of 
the  method  they  have  employed  is  the  same  with  that  suggested  many 
years  ago  by  Davy,  viz.,  that  urea,  when  brought  into  contact  with 
hypochlorite  of  calcium,  is  resolved  into  nitrogen,  carbonic  anhydride, 
and  water  in  virtue  of  the  following  reaction  : 
2(CON,H,)  +  3(CaCl,0,)=3(CaCy+  2(CO,)  +  N, 
For  the  hypochlorite  of  calcium  Russell  and  West  have  substituted 
a  mixed  solution  of  hypobromite  of  sodium  and  caustic  soda,  which,, 
by  a  like  reaction,  yields  similar  products,  the  carbonic  anhydride,  how- 
ever, being  absorbed  by  the  caustic  alkali.  Working  with  the  latter 
solution,  I  have  recently  made  many  experiments  which  have  conducted 
to  the  conclusion,  that  at  a  given  temperature  and  pressure  a  given 
quantity  of  urea  always  yields  the  same  volume  of  nitrogen.  Operating 
"  It  seems  that  Linnaeus  ought  to  have  indicated  the  title  of  the  Counts  of  Chin- 
chon,  by  giving  to  his  genus  the  name  Chinchona,  and  not  Cinchona,  which  latter, 
however,  I  adopt,  in  accordance  with  Canon  243  of  the  *  Philosophia  Botanica/ 
which  says:  Nomen  genericum^  etc." 
