REACTIONS  OF  GELATIN.  371 
which  the  salts  of  iodine  are  produced,  their  rich  and  varied 
colors,  and  striking  geometrical  form,  render  them  of  more  than 
ordinary  interest  to  the  chemist :  as  a  few  illustrations  of  this 
may  be  mentioned,  sublimed  iodide  of  arsenic,*  so  closely  resem- 
bling the  leaf  of  the  seaweed,  the  rich  sable  plumes  of  iodide  of 
sulphur, f  biniodide  of  mercury,  and  the  truncated  crystals  of 
iodide  of  ammonium. — London  Pharm.  Jour.,  July,  1865. 
PHENIC  VINEGAR. 
Dr.  Quesneville  gives  the  following  recipe  for  an  antipesti- 
lentiel.  Take  acetic  acid,  (5°,)  900  grammes ;  camphor  in  pow- 
der, 5  grammes ;  crystallized  phenic  acid,  100  grammes.  This 
combination  of  three  antiputrescents  is  said  to  be  extremely 
useful,  and  for  hygienic  purposes  far  superior  to  vinegar  of  the 
four  thieves,  as  toilet  vinegar  was  once  called.  It  has  been  used 
a  good  deal  on  board  ship  to  keep  the  cabins  of  sick  persons 
sweet. — Moniteur  Scientifique,  1865,  p.  515,  from  Chemical 
News,  London,  June  23,  1865. 
REACTIONS  OF  GELATIN. 
By  M.  Carey  Lea,  Philadelphia. 
I  have  been  occupied  at  times  for  some  years  past  with  the 
study  of  this  very  interesting  substance,  and  propose  here  to 
describe  a  new  reaction  which  I  have  observed,  and  which  con- 
stitutes, I  believe,  the  first  colored  reaction  described  as  pro- 
duced between  pure  gelatin  and  a  perfectly  colorless  reagent. 
It  is  true  that  the  precipitate  produced  in  gelatin  solutions  by 
gallotannic  acid  is  much  deeper  in  color  than  the  precipitant ; 
but  the  straw-yellow  color  of  gallotannic  acid  naturally  leads  to 
the  expectation  of  colored  combinations,  whereas  in  the  case  I 
am  about  to  mention,  the  precipitant  is  colorless,  and  the  pro- 
duction of  a  marked  color  seems  to  point  to  a  more  complete 
action  than  that  of  simple  combination. 
*  When  sublimed  in  vessels  containing  air  the  sublimate  will  be  inter- 
spersed with  crystalline  tufts  of  arsenious  acid. 
f  This  sublimate  only  contains  3  per  cent,  of  sulphur,  according  to 
Rose. 
