HOW  TO  PRESCRIBE  AND  HOW  TO  WEIGH  IN  GRAINS.  361 
merals  would  be  to  get  into  a  calculation  for  no  other  purpose 
than  to  get  out  of  it  again. 
Suppose  a  man  has  to  perform  a  simple  chemical  determina- 
tion,— say,  the  solid  contents  of  a  decigallon  of  water  from  some 
water-works, — first  he  weighs  a  capsule,  which  equals,  say, 
413-98  grains;  (2)  after  evaporating  the  water  therein,  and 
drying  at  250°,  it  weighs  416-4  grains;  (3)  after  drying  still 
further,  416-35  grains.  This  number  is  adopted,  giving  a^  the 
total  solid  impurity,  viz.,  the  difference  between  the  first  and 
third  weighing,  multiplied  by  10,  as  per  gallon,  23-7  grains. 
These  results  are  seen  at  a  glance.  But  what  chemist,  except 
his  head  were  stuffed  with  straw,  would  write  down,  instead  of 
the  above  figures,  "  Weight  of  capsule,  3vj.,  Bij.,  gr.  xiij.,  et 
xcviij.  partes  grani  e  centum  ;  after  evaporation,  3vj.,  Bij.,  gr. 
xvj.,  et  xxxv.  partes  grani  e  centum  ;  weight  of  solid  residue 
per  gallon,  Bj.,  gr.  iij.,  et  septem  partes  grani  e  decern?" 
If  chemists  do  not  vex  their  souls  with  these  antique  intrica- 
cies, why  should  we  ?  But  if  the  manner  of  expressing  quantities 
in  grains  be  easy,  infinitely  more  so  is  the  actual  weighing,  if, 
instead  of  the  odious  Apothecaries'  weights,  we  have  a  set  of 
plain  grain-weights. 
With  the  Apothecaries' weights  they  give  3ij.,  Bij.,  Z  ss., 
Bj..,  Bss.,  besides  grain-weights  stamped  to  represent  6,  6,  4,  3, 
2,  and  1  grain. 
It  is  practically  difficult  to  distinguish  between  Bij.  and  3ss., 
and  it  takes  up  a  good  deal  of  calculation  to  make  up  odd  num- 
bers of  grains. 
A  box  of  good  chemical  grain- weights,  on  the  contrary,  has 
them  in  regular  sets  of  four,  out  of  which  any  combination  can 
be  made  immediately  by  the  simplest  process  of  addition.  The 
grain  weights  are  made  of  wire,  bent  in  such  a  way  that  each 
gives  its  value  at  a  glance. 
The  highest  set  of  weights,  for  hundreds  of  grains,  is — 600, 
300,  200,  100.  The  next,  for  tens— 60,  30,  20, 10.  The,third, 
for  grains  (of  platinum  wire) — 6,  3,  2,  1.  The  fourth,  for 
tenths  (of  platinum  wire) — »6,  -3,  «2,  •!.  Hundredths  may  be 
had  in  gold  wire,  but  are  not  necessary,  and  tenths  can  seldom 
be  wanted  in  dispensing. 
It  may  be  seen  at  a  glance,  first,  that  the  series  of  "  tens  of 
