ON  WEIGHING  VERY  SMALL  PORTIONS  MATTER.  151 
skimmed  carefully,  and  the  alloy  cast  in  a  mould  of  damp  sand 
or  metal.  The  oreide  melts  at  a  temperature  low  enough  to 
allow  its  application  to  all  kinds  of  ornamentation  ;  it  has  a  fine 
grain,  is  malleable,  and  capable  of  taking  the  most  brilliant 
polish  ;  when,  after  a  time,  it  becomes  tarnished  from  oxidation, 
its  brilliancy  may  be  restored  by  a  little  acidulated  water.  If  the 
zinc  is  replaced  by  tin,  the  metal  will  be  still  more  brilliant." 
Cosmos. 
An  ingot  of  this  new  Similor  has  been  exhibited  in  the  Frank- 
lin Institute,  and  it  appears  really  to  have  the  qualities  which 
are  here  claimed  for  it,  and  to  be  well  worthy  of  the  attention  of 
those  who  are  engaged  in  ornamentation  in  metal  Ed.  F. 
Inst.  Journ. 
THE  ESTIMATION  OF  THE  WEIGHTS  OP  VERY  SMALL  PORTIONS 
OF  MATTER. 
By  Alfred  McMayer, 
Professor  of  Physics  and  Chemistry  in  the  University  of  Maryland. 
The  chemist,  in  the  course  of  his  analytical  investigations, 
often  meets  with  what  are  called  traces  of  substances  ;  by  which 
is  .generally  understood,  quantities  of  matter  too  minute  to  have 
any  appreciable  weight  in  the  analytical  balance.  Now  it  some- 
times happens  that  these  traces  are  of  as  much  importance  con- 
sidered scientifically  and  commercially  as  the  ingredients  present 
in  appreciable  quantities  ;  and  in  order  to  estimate  these  small 
portions  of  matter,  he  is  often  obliged  to  go  over  his  work,  using 
very  considerable  weights  of  substances,  whereby  his  time  and 
care  are  nearly  doubled.  It  was  this  inconvenience  that  first  in- 
duced me  to  try  to  determine  in  one  operation  the  components 
present  in  large  and  in  very  minute  quantities ;  and  although  I 
have  succeeded  beyond  my  expectations,  I  am  confident  that  the 
process  is  susceptible  of  improvement,  both  as  regards  sensibility 
and  accuracy. 
After  making  many  investigations  on  the  sensibility  of  the 
most  delicate  levers  as  to  small  weights,  this  method  was  found 
far  too  rough.  It  then  occurred  to  me  that  if,  instead  of  using 
the  opposing  force  of  gravity  through  the  intervention  of  a  lever, 
we  could  oppose  to  the  gravitating  effect  of  the  matter  the  force 
of  perfect  elasticity  as  manifested  in  filaments  of  glass,  we  might 
