78 
Colloids  and  Crystals. 
j  Am.  jour,  Pharth. 
\   February,  1914. 
for  the  potter  by  an  empirical  process  which  involves  the  action  of 
protective  colloids  derived  from  decaying  vegetable  matter.  The 
addition  of  gelatin  in  making  ice  cream  depends  upon  its  protective 
action  in  preventing  the  growth  of  ice  crystals,  which  would  make 
the  product  "  gritty."  Without  doubt  protective  action  plays  an 
important  role  in  the  cleansing  action  of  soap.  This  has  been 
made  clear  by  some  recent  experiments  of  Spring.8  Lampblack, 
freed  from  oil  by  long  washing  with  alcohol,  ether,  and  benzene, 
forms  a  rather  stable  suspension  in  water,  but  the  lampblack  is  de- 
tained by  a  paper  filter.  If  the  filter  is  now  reversed,  so  that  the 
blackened  surface  is  outward,  and  water  poured  through  it,  the  lamp- 
black is  not  removed,  but  a  dilute  soap  solution  removes  the  coating 
and  cleanses  the  filter  at  once.  Finally,  lampblack  suspended — or  col- 
loidally  dissolved — in  soap  solution,  passes  through  a  filter  unchanged. 
It  is  of  much  practical  interest  that  there  is  a  well-marked  optimum 
in  the  concentration  of  the  soap  required  to  protect  the  lampblack. 
A  one  per  cent,  soap  solution  is  the  most  efficient.  In  two  per  cent, 
soap  solution  lampblack  sinks  about  as  rapidly  as  in  pure  water. 
VI. 
We  have  already  considered  the  probable  actual  condition  of  the 
particles  in  a  colloidal  solution  and  have  concluded  that,  for  the 
present,  no  very  definite  information  is  obtainable  about  the  matter. 
We  must  now  return,  for  a  moment,  to  the  subject  in  order  to  allude 
to  the  thesis  so  brilliantly  advocated  by  van  Weimarn,  the  Russian 
investigator,  who  holds  that  the  particles  are  of  necessity  minute 
crystals  and  that  there  is,  in  fact,  no  such  thing  as  amorphous  matter. 
He  even  goes  so  far  as  to  state  that  substances  like  air  and  water 
are  in  a  "  dynamic  crypto-crystalline  condition,"  though  I  have  been 
unable  to  understand  what  he  means  by  this  statement. 
Briefly,  the  evidence  that  van  Weimarn  adduces  to  the  support 
of  his  hypothesis  is : 
(1)  That  colloid  particles  will  grow  to  crystals  if  provided  with 
the  proper  nourishment,  namely,  a  dilute  solution  of  the  same 
substance. 
(2)  That  colloid  particles  are  capable,  when  introduced  into 
8  Kolloid  Zeitschrift,  vol.  4,  p.  161  (1909);  Kolloid  Zeitschrift,  vol.  6, 
pp.  11,  109,  164  (1910). 
