82  Whiting  and  Its  Manufacture.  {^T™/im?xm' 
Upon  examination  of  this  table,  it  will  be  seen,  from  the  very  mode 
of  preparation,  i.  e.,  deposition  by  gravity  on  suspension  in  water, 
that  the  density  of  each  product  decreases,  as  the  product  becomes 
finer.  Creta  Pra?parata  (U.  S.  P.)  appears  to  be  made  from  Cliffstone 
Paris  White,  and,  in  density,  Calcii  Carbonas  Prsecipitatus  (U.  S.  P.) 
resembles  American  Paris  White.  A  decrement  of  the  amount  of 
silica  present  as  each  sample  becomes  finer,  will  also  be  noticed,  and 
the  extreme  difficulty  of  the  total  separation  of  silica,  by  the  present 
method  of  manufacture,  may  be  readily  seen,  when  a  comparison  is 
made  between  the  specific  gravities  of  that  substance  in  its  natural 
amorphous  condition  with  whiting  densities.  Unfortunately,  in  the 
present  instance,  the  two  main  authorities  depended  upon  differ  to 
some  extent  with  each  other.  Fownes,4  indefinitely,  gives  its  density 
as  somewhat  above  2,  while  Frankiand  and  Japp5  state  it  to  be  2.3. 
It  is  more  than  probable  that  the  latter  figure  is  nearer  the  correct  one, 
though  it  may  be  still  higher  since  Fownes1  also  gives  2*66  as  the 
specific  gravity  of  artificial  amorphous  silica,  while  Frankiand  and 
Japp2  claim  the  same  to  have  a  specific  gravity  of  2*2.  There  is  then, 
clearly,  an  error  in  density  on  the  part  of  one  or  both.  Of  moisture 
there  was  none  in  the  samples  examined,  as  obtained  by  the  writer 
from  the  manufacturer's  hands.  Whether  all  makes  will  bear  out 
this  record  is  not  known,  as  only  the  one  make  was  examined. 
The  point  suggests  itself,  that  if  a  form  of  calcium  carbonate  is 
desired  for  medicinal  uses  and  is  employed  under  the  term  "  Creta 
Prseparata,"  which  at  present  is  made  from  Cliffstone  Paris  White, 
containing  4  per  cent,  of  silica,  why  not  make  a  purer  preparation  by 
using  American  Paris  White,  containing  only  one-half  that  quantity 
of  silica,  which  certainly  must  be  preferable  for  such  uses.  A  sample 
of  Creta  Prseparata,  made  from  American  Paris  White,  in  the  familiar 
nodular  form  is  here  presented  as  C  No.  3.  The  impossibility  of 
making  these  cones  to  keep  permanently  hard,  when  prepared  from 
precipitated  calcium  carbonate,  may  here  be  mentioned,  and  arises 
from  the  fact  that  under  the  microscope,  diffused  through  water,  the 
powder  of  precipitated  carbonate  appears  in  minute  crystals,  all  of 
equal  size,  while  in  the  form  of  whiting,  under  the  same  conditions,  the 
appearance  is  that  of  minute  crystals  widely  different  in  sizes,  and  it 
seems  to  be  a  physical  law  that  when  small  crystals  of  equal  size  are 
4  Fownes  Elementary  Chemistry  ( Watts)  p.  224. 
6  Frankiand  and  Japp's  Inorganic  Chemistry,  p.  317. 
