Am' M?y  52irm"  \  Analytical  Characteristics  of  Talcum.  317 
Fineness  of  Subdivision. — This  characteristic  is  determined  by 
comparative  tests  under  the  microscope.  A  powdered  talcum  which 
is  coarser  under  the  microscope  will  be  harsher  to  the  touch  and 
unsatisfactory  in  the  "thumb  and  forefinger"  test.  No  definite 
standard  of  size  of  particle  can  be  laid  down ;  frequent  comparative 
microscopic  observations  in  conjunction  with  the  "thumb  and  fore- 
finger" test  being  required  to  demonstrate  the  value  of  the  micro- 
scopic method  of  testing  the  fineness  of  subdivision. 
Feel  Between  Thumb  and  Forefinger. — This  is  known  as  the 
"thumb  and.  forefinger"  test.  The  method  of  making  this  test  is1 
outlined  above  under  "Harsh  Associated  Substances."  The  phar- 
macist will  realize  the  importance  of  this  test  when  he  recalls  that 
the  prospective  customer  when  considering  the  purchase  of  a 
powdered  talcum  will  invariably  make  this  test  either  between  the 
thumb  and  forefinger  or  between  the  palms  of  the  hands  after  first 
ascertaining  the  odor  of  the  powder.  The  perfuming  of  toilet  tal- 
cums is  foreign  to  the  subject  of  this  article  but  must  be  considered 
of  even  more  importance  than  the  analytical  characteristics  of  the 
powder  used  in  making  the  product,  provided  the  powder  passably 
conforms  to  the  analytical  tests. 
Whiteness. — Whiteness,  to  a  certain  degree,  is  measured  by 
fineness  of  subdivision;  the  finer  the  subdivision  the  whiter  the 
powder.  This  is  only  true,  however,  of  talcum  from  the  same  natural 
source.  The  comparative  color  of  talcums  from  different  sources 
must  be  considered  a  separate  problem.  Whiteness  is  best  deter- 
mined comparatively  by  placing  a  small  mound  of  the  powder  under 
test  on  a  white  sheet  of  paper  and  comparing  its  color  with  that  of 
a  similar  mound  of  a  satisfactory  standard  powder  on  the  same 
sheet  of  paper.  Whiteness  of  product  is  a  very  important  matter, 
as  the  trade  prefers  a  snowy-white  product. 
Adherence  Test. — A  desirable  characteristic  of  toilet  talcum 
consists  of  its  ability  to  adhere  well  to  the  skin  when  rubbed 
thereon,  because  one  of  the  reasons  for  the  use  of  talcum  is  its 
covering  power.  Aside  from  this,  toilet  talcum  must  adhere  well 
from  the  standpoint  of  economy,  the  more  adherent  product  pos- 
sessing greater  covering  power  and  therefore  requiring  the  use  of 
less  material  for  a  given  amount  of  surface.  The  adherence  test 
can  be  applied  by  rubbing  the  talcum  upon  the  under  side  of  the 
