Am'jJa0nuy'iSiarm"}  Gleanings  from  the  German  Journals.  17 
relative  positions ;  or,  to  speak  more  correctly,  the  relative  position 
of  the  P.  A.  of  the  selenite  to  the  beam  of  light  from  the  mirror 
decides  the  more  or  less  intense  coloration.  With  any  other  sky, 
the  polarization  is  not  observed. 
This  observation  is  useful  in  so  far  as  to  enable  the  possessors  of 
microscopes,  without  substage  facilities,  to  polarize  fairly  well — 
under  the  circumstances — and  the  proper  condition  of  the  sky  is 
often  obtained  in  our  latitude.  H.  M.  Wilder. 
Philadelphia,  November  20,  18 go. 
GLEANINGS  FROM  THE  GERMAN  JOURNALS. 
By  Frank  X.  Moerk,  Ph.G. 
Cholesterin. — Of  the  homologues  and  isomers  of  this  compound 
occurring  in  the  vegetable  and  animal  kingdoms  only  the  iso-choles- 
terin  has  been  more  closely  studied  and  differences  from  cholesterin 
noted.  To  finally  establish  the  formula  of  cholesterin,  K.  Ober- 
miiller  made  a  series  of  derivatives  from  which  the  formula  C27H45OH 
follows.  Of  these  compounds  the  propionate  C27H45C3H702  affords 
a  means  of  distinguishing  cholesterin  from  allied  substances.  The 
cholesterin  is  first  separated  from  the  fat  or  oil  by  evaporating  the 
ethereal  solution  obtained  by  agitating  the  aqueous  soap  solutions 
with  ether,  or  in  the  new  method  of  saponification  (Am.  Jour. 
Pharm.,  1890,  490)  evaporating  at  once  the  ethereal  solution  after 
the  precipitation  of  the  soap ;  a  small  quantity  of  this  dried 
ethereal  residue  is  melted  in  a  dry  test  tube  with  2  or  3  drops  of 
propionic  anhydride  over  a  small  flame.  A  very  characteristic  play 
of  colors  is  produced  jf  a  small  quantity  of  the  cold  fused  mass  is 
heated  on  a  glass  rod  and  allowed  to  cool,  holding  the  rod  in  front 
of  a  dark  background ;  first  violet,  gradually  blue,  green,  dark 
gray,  orange,  carmine-red  and,  finally,  copper-red.  The  blue  and 
green  colors  continue  for  some  time ;  by  suddenly  cooling  the  fused 
mass  the  copper-red  color  results  lasting  for  some  time.  The  blue 
color  alone  is  obtainable  if  the  cholesterin  propionate  be  placed  in 
a  test  tube  and  melted  by  immersion  in  a  glycerin  bath  at  980  C. 
These  colors  are  to  be  observed  by  reflected  light,  as  by  transmitted 
light  the  complementary  colors  are  seen. 
Cholesterin  benzoate  C27H45C7H502  is  easily  obtainable  by  heating 
cholesterin  to  1600  C.  for  a  few  minutes,  with  a  slight  excess  of 
benzoyl  chloride ;   from  an  ether-alcoholic  solution  characteristic 
