Amja°ne?iS2arm-}       Artificial  Coloring  of  Crystals.  321 
above  purpose.  The  twisting  of  the  head  into  an  uncomfortable 
position,  the  great  fatigue  to  the  eyes,  and  the  by  no  means  easy 
task  of  viewing  both  image  and  pencil  at  the  same  time,  add  to  the 
troubles  of  making  a  faithful  likeness  of  the  object  on  paper. 
To  those  especially  who  do  not  possess  a  camera  lucida,  or  Beale's 
instrument,  and  to  microscopists  generally,  I  recommend  the  follow- 
ing arrangement  of  ordinary  apparatus  :  The  microscope  body  is 
placed  in  a  horizontal  position,  and  the  mirror  removed  from  its 
substage  attachment.  The  microscope  slide  having  been  placed  on 
the  stage,  the  illuminant  (lamplight  for  choice)  is  "condensed  "  on 
the  slide  by  means  of  a  "bull's  eye  "  in  the  same  way  as  for  photo- 
micrography. Care  must  be  taken  to  "centre  "  the  light.  The 
concave  mirror  is  then  attached  to  the  front  of  the  eye-piece  of  the 
microscope  by  a  piece  of  thin  wood  or  a  spring,  and  has  its  surface 
at  an  angle  of  about  45  0  with  the  plane  of  the  anterior  glass  of  the 
ocular.  The  imagers  thus  projected  on  to  the  paper  beneath.  No 
distortion  will  occur  if  the  outer  ring  of  light  is  perfectly  circular.  A 
dark  cloth,  such  as  photographers  use,  is  thrown  over  the  draughts- 
man's head  and  also  over  the  body  of  the  microscope,  and  all  light 
excluded  save  that  through  the  microscope  lenses.  Any  section  can 
thus  be  easily,  rapidly,  and  comfortably  drawn,  and  accurate  repre- 
sentations of  objects  magnified  up  to  500-600  diameters  can  be 
obtained. 
ARTIFICIAL  COLORING  OF  CRYSTALS.1 
By  O.  Lehmann. 
Senarmont  discovered  that  salt  crystals  may  be  colored  by  cer- 
tain organic  dyes  without  any  change  in  the  form  or  homogeneity 
of  the  crystal.  The  author  has  on  former  occasions  made  similar 
observations  with  other  inorganic  and  organic  compounds,  and  in 
order  to  ascertain  something  more  with  reference  to  the  conditions 
under  which  this  phenomenon  takes  place,  has  now  made  a  large 
number  of  experiments  on  the  artificial  coloration  of  crystals.  The 
crystals  made  use  of  were  those  of  certain  organic  acids,  such  as 
succinic,  protocatechuic,  and  phthalic  acids,  and  these  were  colored 
by  meaiio  of  different  organic  dyes.  The  author  summarizes  his 
results  as  follows : 
The  crystals  always  become  darker  in  color  than  the  solution 
1  Zeit.  physikal.  Chem.,  8,  543-553.    Jour.  Chem.  Soc,  March.,  p.  269. 
