874 
COLORS  OF  VEGETABLES. 
any  pointed  instrument  a  very  little  cement  is  removed  from  one 
part,  so  that  more  fluid  may  escape  as  the  cover  is  pressed  down 
gently  into  the  cement.  The  pressure  must  be  removed  very 
gradually,  or  air  will  enter  through  the  hole.  A  bubble  of  air 
entering  in  this  manner  may  often  be  expelled  again  by  pressure, 
or  it  may  be  driven  out  by  forcing  in  more  fluid  through  a  very 
fine  syringe  at  another  part  of  the  cell,  but  it  is  far  better  to 
prevent  the  entrance  of  air  in  the  first  instance.  The  edge  of 
the  glass  cover  being  thoroughly  embedded  in  the  cement,  the 
small  hole  is  to  be  carefully  plugged  up  by  a  small  piece  of 
cement,  and  the  cell  allowed  to  stand  perfectly  still  for  a  short 
time,  when  it  may  be  very  gently  wiped  with  a  soft  cloth.  The 
edges  of  the  cement  may  be  smoothed  by  the  application  of  a 
warm  iron  wire,  and  any  superabundance  removed  with  a  sharp 
knife.  A  little  Brunswick  black  or  other  liquid  cement  may  be 
applied  to  the  edges  for  the  purpose  of  giving  the  whole  a  neater 
appearance.  The  cement  is  made  as  follows:  A  certain  quantity 
of  india-rubber  scraps  is  carefully  melted  over  a  clear  fire  in  a 
covered  iron  pot.  When  the  mass  is  quite  fluid,  finely  powdered 
lime,  having  been  slacked  by  exposure  to  the  air,  is  to  be  added 
by  small  quantities  at  a  time,  the  mixture  being  well  stirred. 
When  moderately  thick,  it  is  removed  from  the  fire  and  well 
beaten  in  a  mortar,  and  moulded  in  the  hands  until  of  the  con- 
sistence of  putty.  It  may  be  colored  by  the  addition  of  ver- 
milion or  other  coloring  matter.  This  cement  answers  well  for 
fixing  on  the  glass  tops  of  large  preparation  jars,  but  if  mode- 
rately strong  spirit  be  used,  a  little  air  must  be  permitted  to  re- 
main in  the  jar. — From  a How  to  Work  with  the  Microscope" 
by  Lionel  S.  Beale  and  Chem,  New?,  May  7,  1864. 
COLORS  OF  VEGETABLES. 
Prof.  Rochleder  *  states  that  on  comparing  the  properties  of 
rottlerin  with  those  of  chrysophanic  acid  and  of  purpurin,  a 
close  resemblance  becomes  apparent,  such  as  generally  only  takes 
place  between  consecutive  members  of  a  homologous  series.  The 
formulas  of  these  bodies  (Cis  IU  06  for  pupurin,  C:o  Hs  (X,  for 
Chrysophan,  C22  H10  05  for  rotteilin),  likewise  favor  the  afctump- 
