Am.  Jour.  Pharm.  ) 
July,  1920.  ) 
Book  Reviews. 
515 
For  many  years,  physicists  and  chemists  were  wont  to  speak  of  the 
two  types  as  representing  different  classes  of  substances,  but  we 
now  know  that  the  differences  are  those  of  condition  and  that  any 
substance  may  assume  either  state.  Colloidal  conditions  of  even 
the  very  active  elements,  such  as  sodium,  can  be  obtained.  It 
appears,  indeed,  that  some  of  the  phenomena  that  have  been  desig- 
nated as  liquid  crystals,  may  be  really  due  to  colloid  suspension. 
The  author  of  this  book  is  so  well  known  in  the  field  to  which  it  is 
devoted  that  we  may  feel  sure  that  it  will  be  of  high  merit.  It  is 
especially  so  because  it  deals  with  a  phase  of  the  subject  that  has 
not  received  as  much  attention  as  needed,  namely,  the  actual  work 
in  preparing  and  studying  colloids.  A  good  deal  of  the  literature 
has  been  taken  up  with  the  theory  and  applications,  and  a  book, 
such  as  is  here  presented,  which  gives  practical  details  of  many  experi- 
ments will  be  especially  welcome  to  the  older  chemist  whose  studies 
date  from  time  when  phenomena  were  merely  given  passing  notice 
in  the  instruction.  In  fact,  as  one  writer  lately  said,  sorre  of  the 
most  important  facts  in  physical  chemistry  were  presented  in  a 
highly  indirect  way.  AUotropism  was  discussed  always  under 
ozone,  dimorphism  under  sulphur,  colloid  state  under  silicic  acid, 
and  catalysis  in  connection  with  the  production  of  oxygen  from 
potassium  chlorate. 
The  work  has  nineteen  chapters,  each  devoted  to  a  special  phase 
of  colloid  phenomena.  The  first  chapter  takes  up  the  general  methods 
of  procedure,  pointing  out  the  great  importance  of  cleanliness,  and 
the  liability  of  error  from  the  inferiority  of  the  glass  used  in  many 
of  the  laboratory  vessels.  Test-tubes  are  often  found  that  in  a  short 
time  will  communicate  enough  alkali  to  pure  water  to  produce  a 
pink  tint  with  phenolphthalein.  Such  tubes  are  quite  unfit  for  use. 
The  difficulty  of  cleaning  vessels  after  certain  experiments  is  pointed. 
Thus,  while  suspensoid  sols  are  generally  easily  removed,  the  emul- 
soid  forms  are  much  more  difficult.  Traces  of  gelatin  or  albumin 
are  difficult  to  remove  and  very  objectionable  if  not  removed.  A 
special  chapter  is  given  to  the  methods  of  producing  the  curious  rings 
known  as  the  Liesegang  phenomenon.  The  original  method  with 
chromated  gelatin  and  silver  nitrate  is  given  and  then  several  other 
forms,  of  which  those  with  silicic  acid  gel  will  be  of  special  interest 
to  mineralogists,  since  banded  deposits  are  not  infrequently  noted 
in  minerals. 
The  book  is  a  valuable  addition  to  the  literature  of  the  subject. 
