32 
Aluminium  Weights. 
f  Am.  Jour.  Pharm 
X     Jan.  2,  1871. 
precipitated  in  the  free  state  as  a  blackish  colored  precipitate ;  the 
iodine  thus  deposited  is  next  freed  from  adhering  fluid  by  placing  it  in 
an  earthenware  vessel,  at  the  bottom  of  which  are  placed  several  lay- 
ers of  clean  sand,  so  arranged  that  the  size  of  its  grains  decrease 
from  the  bottom  upwards.  On  the  top  of  this  sand  the  wet  iodine  is 
put,  the  sand  acting  as  a  sponge  to  absorb  the  fluid.  When  the  iodine 
has  become  dry,  it  is  carefully  removed  from  the  vessel,  but  a  thin 
layer  of  it  is  left  on  the  sand ;  the  crude  iodine  is  refined  by  sublima- 
tion. The  inventor  of  this  process,  a  Frenchman  named  Thiercelin, 
has  recently  found  that,  instead  of  using  sulphurous  acid,  it  is  more 
advantageous  to  employ  nitrous  acid,  obtained  in  the  shape  of  nitrite 
of  potassa  by  the  ignition  of  a  mixture  of  1  part  of  charcoal  and  5 
of  nitrate  of  potassa  ;  the  nitrite  obtained  yields,  when  mixed  with 
the  mother-liquor,  a  precipitate  containing  some  80  per  cent,  of 
iodine. — Chem.  JSFews,  London,  Nov.  4,  1870 
ON  ALUMINIUM  WEIGHTS. 
By  Dr.  T.  L.  Phipson,  F.O.S. 
For  the  last  ten  years — that  is,  since  May,  1860 — I  have  made  use 
of  a  set  of  aluminium  (division  of  the  gramme)  weights.  On  the 
average  these  weights  have  been  used  at  least  twice  or  three  times  a 
day  for  a  period  of  somewhat  more  than  ten  years.  They  were  sup- 
plied by  MM.  Collet,  Freres,  of  Paris.  Latterly,  I  have  tested  them 
and  found  them  as  accurate  as  the  day  on  which  they  were  first  used. 
They  are  almost  as  brilliant  as  when  new.  The  larger  weights  0.5, 
0.2,  and  0.1  gramme  show  slight  traces  of  tarnish,  but  their  weights 
are  still  quite  accurate. 
During  this  period  of  ten  years  these  weights  have  never  been 
touched  except  by  a  pair  of  soft  brass  nippers,  and  they  have  never 
been  left  exposed  to  the  air  for  more  than  a  few  minutes  at  a  time. 
However,  they  have,  of  course,  been  exposed  for  a  minute  or  two  at 
intervals  to  an  atmosphere  more  or  less  impregnated  with  acid  or  al- 
kaline vapors,  and  if  we  add  these  odd  minutes  together,  it  will  be 
found  that  these  gramme  divisions  in  aluminium  have  had  to  undergo 
a  considerable  amount  of  "  atmospheric  influence"  during  the  period 
of  which  I  speak. 
I  need  scarcely  say  what  a  luxury  it  is  to  use  such  large  weights  as^ 
