318  Analytical  Characteristics  of  Talcum.   I  Am\J°aUy '  i£?rm' 
forearm  or  other  smooth,  non-hairy  surface,  in  comparison  with  a 
satisfactory  standard  product.  Considerable  experience  gained 
through  numerous  comparative  tests  is  necessary  in  order  to  develop 
a  standard  and  demonstrate  the  value  of  this  test. 
"Pearliness." — "Pearliness"  is  one  of  the  desirable  qualities  of 
a  toilet  talcum.  It  consists  of  the  ability  of  the  product  to  pro- 
duce a  pearly  or  wax-like  "bloom"  on  the  skin.  Powdered  talcum 
produces  this  effect  by  breaking  up  the  reflection  of  the  light  which 
approaches  total  reflection  from  a  shiny  skin.  This  it  does  by  super- 
imposing innumerable  minute  reflecting  surfaces  over  the  single, 
almost  continuous,  reflecting  surface  represented  by  a  "shiny"  skin. 
The  test  for  "pearliness"  is  made  at  the  same  time  as  the  adherence 
test,  and  like  the  adherence  test,  considerable  experience  with  it  is 
required  to  demonstrate  its  value  and  to  develop  a  standard. 
Density. — "Flufnness,"  or  low  density  is  desired  by  an  average 
user  of  toilet  talcum.  Powdered  talcums  vary  considerably  in  this 
respect.  These  variations  are  due  to  differences  in  chemical  and 
physical  characteristics  of  the  rock  and  the  fineness  of  subdivision, 
adhering  ability  and  moisture  content  of  the  powder.  Maximum 
flufnness  is  desirable,  therefore,  a  standard  method  of  testing  for 
density  and  an  arbitrary  standard,  based  upon  examination  of 
satisfactory  materials,  must  be  established.  The  method  of  testing 
for  density  which  has  given  excellent  results  in  the  laboratory  with 
which  I  am  connected,  consists  of  determining  the  weight  of  the 
powder  which  is  held  by  a  standard  size  cup  when  the  cup  is  filled 
with  powder  under  specified  conditions.  For  this  purpose  a  small, 
cylindrical,  metal  crucible  is  used ;  metal  being  preferred  to  glass 
or  porcelain  for  the  reason  that  breakage  would  necessitate  the 
extra  trouble  of  determining  a  new  standard.  This  metal  crucible 
or  cup  is  used  as  follows :  The  cup  is  weighed,  the  powder  is  poured 
in  until  it  is  piled  up  over  the  top ;  the  excess  is  scraped  off  with  a 
spatula  and  the  crucible,  so  filled,  is  weighed  again.  As  an  ar- 
bitrary standard  we  have  adopted  a  powdered  talcum  of  which  our 
cup  holds  9  grams,  having  determined  that  such  a  talcum  will 
possess  a  desirable  "flufnness."  In  making  the  determination  of 
density  care  must  be  taken  not  to  shake  or  tamp  down  the  powder 
since  the  object  of  the  test  is  to  determine  the  density  or  flufnness 
of  the  powder  in  a  loose  condition  such  as  exists  during  its  practical 
