60 
Lecture  Experiments. 
f  Am.  Jour.  Pharm. 
\     Feb.  1,  1871. 
When  a  concentrated  solution  of  iodine  green  in  alcohol  is  evapo- 
rated in  a  glass  evaporating  dish  in  the  air  or,  better,  upon  a  water 
bath,  the  dish  becomes  coated  with  a  homogeneous,  quite  transparent 
varnish,  which  shows  in  transmitted  light  a  magnificent  green  color; 
in  reflected  light,  on  the  other  hand,  a  most  highly  characteristic,  and, 
particularly  after  rubbing,  a  very  decided  red  copper  color. 
When  a  part  of  the  dish  is  gently  warmed,  the  green  changes  into 
violet,  since  the  di-iodmethylate  of  the  trimethyl  rose  aniline  is  con- 
verted with  liberation  of  iodmethyl  into  monoiodmethylate.  Moreover, 
^vhere  the  dish  in  transmitted  lights  appears  of  a  beautiful  violet,  it 
shows  now  in  reflected  light  a  pure  yellow  brazen  color. 
While  green  and  red  on  the  one  hand,  and  on  the  other  blue  and 
yellow  may  be  taken  in  general  as  complementary  colors,  yet  Prof. 
Dove  has  experimentally  demonstrated  in  the  above  mentioned  cases 
that  the  tints  observed  in  the  aniline  dyes  by  transmitted  and  reflected 
light  when  combined  produce  white  light. 
The  green  and  red  colors,  which  the  salts  of  rose  aniline  exhibit  in 
reflected  and  transmitted  light  respectively,  correspond  to  the  com- 
plementary colors  of  a  selenite  plate  of  y  difi'erence  (Gangunterschied) 
looked  at  in  polarized  light  through  a  doubly  refracting  prism  as 
analyser. 
The  soft  green  color  of  iodine  green  in  transmitted  light,  and  the 
copper  red,  which  this  dye  affords  in  reflected  light,  agree  with  the 
colors  of  a  selenite  plate  of  |  difi'erence. 
Finally  the  bluish  violet  color  of  the  methylviolet  arising  from  the 
iodine  green  by  warming,  and  the  brass  color,  which  this  substance  re- 
flects, are  exactly  comparable  to  none  of  the  complementary  colors 
which  are  given  by  the  selenite  plates  in  the  rich  collection  of  Prof. 
Dove.  The  colors  occurring  in  the  case  of  the  last  mentioned  aniline 
■dye  lie  in  the  middle  between  those  observed  in  the  observation  of 
selenite  plates  of  |  and  those  of  ^  difi'erence. 
3.     Tinctorial  power  of  certain  aniline  dyes. 
The  solution  of  a  salt  of  rosaniline  (since  we  are  speaking  here  of 
very  dilute  solutions,  it  matters  not  which  salt  is  employed)  is  diluted 
with  water  containing  some  drops  of  acetic  acid,  until  it  contains  one 
part  of  dye  to  one  million  parts  water  (one  milligramme  to  one  litre 
water.)  It  possesses  still  a  deep  carmine  red.  A  skein  of  silk  moist- 
ened with  dilute  acetic  acid  is  colored  by  this  solution  of  a  beautiful 
red  in  an  instant.    When  the  proportion  of  water  is  increased  to  25 
