368 
VARIETIES. 
crystalline  powder,  having  a  sweetish-slightly  styptic  taste  ;  it  is  readily 
soluble  in  water,  but  almost,  if  not  entirely  insoluble  in  alcohol.  After  long 
exposure  to  light,  it  becomes  of  a  black  color,  whereas  it  preserves  its  grey- 
ish-white crystalline  appearance  if  carefully  kept,  either  in  bottles  or  dark- 
colored  glass,  or  covered  with  paper.  Its  solution  also  becomes  almost 
black  if  long  exposed  to  the  light,  yet  not  so  quickly  as  the  solution  of  ni- 
trate of  silver.  If  perfectly  pure,  it  does  not  discolor  the  skin,  or  linen,  as 
the  nitrate  of  silver  does ;  nor  does  it  possesss  the  same  power  in  coagula- 
ting albumen  as  the  nitrate  does.  Dr.  J.  Delioux  has  administered  this 
compound  salt  in  many  diseases,  the  results  of  which  trials  he  has  made 
known  to  the  profession  in  one  of  the  medical  journals  of  Paris.- — Annals 
of  Pharmacy. 
Photography  : — The  Fixation  of  Colors. — M.  Niepec  de  Saint- Victor  laid 
before  the  Academy  of  Sciences,  at  the  sitting  of  the  8th  of  November,  da- 
guerreotypes upon  which  he  had  succeeded  in  fixing,  in  a  manner  more  or 
less  permanent,  colors  by  the  camera-obscura.  M.  Niepec  states,  that  the 
production  of  all  the  colors  is  practicable,  and  he  is  actively  engaged  in  en- 
deavoring to  arrive  at  a  convenient  method  of  preparing  the  plates.  "  I 
have  begun,"  he  says,  "  by  reproducing  in  the  dark  chamber,  colored  en- 
gravings, then  artificial  and  natural  flowers,  and  lastly  dead  nature — a  doll, 
dressed  in  stuffs  of  different  colors,  and  always  with  gold  or  silver  lace.  I 
have  obtained  all  the  colors ;  and,  what  is  still  more  extraordinary  and 
more  curious  is,  that  the  gold  and  silver  are  depicted  with  their  metallic 
lustre,  and  that  rock-crystal,  alabaster,  and  porcelain,  are  represented  with 
the  lustre  which  is  natural  to  them.  In  producing  the  images  of  precious 
stones  and  of  glass  we  observe  a  curious  peculiarity.  "We  have  placed  be- 
fore the  lens  a  deep  green,  whieh  has  given  a  yellow  image  instead  of  a 
green  one  ;  whilst  a  clear  green  glass  placed  by  the  side  of  the  other  is  per- 
fectly reproduced  in  color."  The  greatest  difficulty  is  that  of  obtaining 
many  colors  at  a  time  ;  it  is,  however,  possible,  and  M.  Niepec  has  frequent- 
ly obtained  this  result.  He  has  observed,  that  bright  colors  are  produced 
much  more  vividly  and  much  quicker  than  dark  colors : — that  is  to  say, 
that  the  nearer  the  colors  approach  to  white  the  more  easily  are  they  pro- 
duced, and  the  more  closely  they  approach  to  black  the  greater  is  the  diffi- 
culty of  reproducing  them.  Of  all  others  the  most  difficult  to  be  obtained 
is  the  deep  green  of  leaves  ;  the  light  green  leaves  are,  however,  reproduced 
very  easily.  After  sundry  other  remarks,  of  no  peculiar  moment,  M.  Nie- 
pec de  Saint-Victor  informs  us,  that  colors  are  rendered  very  much  more 
vivid  by  the  action  of  ammonia,  and  at  the  same  time  this  volatile  alkali 
appears  to  fix  the  colors  with  much  permanence.  These  results  bring  much 
more  near  than  hitherto  the  desideratum  of  producing  photographs  in  their 
natural  colors.  The  results  are  produced  upon  plates  of  silver  which  have 
been  acted  upon  by  chloride  of  copper  or  some  other  combination  of 
chlorine.  The  manipulatory  details  have  not  been  published,  but  we  un- 
derstand they  are  very  easy. — Jour.  Frank.  Inst,  from  the  London  Athenaeum* 
