MODIFICATION  OF  CHEMICAL  AFFINITY. 
329 
was  found  to  be  affected  by  the  admixture  of  a  chloride,  bromide, 
or  iodide  according  to  the  nature  and  the  mass  of  the  salt  added, 
and  the  addition  of  sulphuric,  phosphoric,  nitric  and  other  acids 
was  found  to  produce  a  fluorescence  in  solutions  either  of  hydro- 
chlorate  of  quinine,  or  of  sulphate  which  had  been  rendered  non- 
fluorescent  by  hydrochloric  acid.  Similar  results  were  obtained 
with  quinidine ;  and  somewhat  analogous  ones  with  the  organic 
bases  contained  in  horse-chestnut  bark,  and  in  tincture  of  stra- 
monium. An  experiment  is  also  narrated  showing  that  the  same 
laws  hold  good  in  respect  to  compound  ethers  as  to  salts  having 
metallic  bases,  alcohol  being  employed  as  the  solvent. 
Besides  the  very  diversified  substances  already  mentioned  in 
this  abstract,  several  others,  such  as  lead,  mercury,  zinc,  potash, 
soda,  baryta,  lime  and  ammonia,  are  shown  by  a  more  indirect 
proof  to  enter  into  compounds  which  obey  the  same  laws.  Hence 
it  is  concluded  that  what  was  observed  in  reference  to  the  ferric 
salts  holds  good  very  generally,  if  not  universally. 
The  bearing  of  certain  other  phenomena  upon  the  question  at 
issue  was  also  examined.  The  fact  that  precipitation,  when  it 
occurs,  gives  rise  to  a  perfect  interchange  of  bases  and  acids,  is 
equally  consistent  with  either  Bergmann's  or  Berthollet's  theory  ; 
but  not  so  is  the  fact  that  two  soluble  salts  cannot  be  mixed  with- 
out the  occurrence  of  precipitation,  if  one  of  the  products  that 
may  be  formed  is  an  insoluble  salt.  The  only  recorded  exception 
to  this  law,  which  occurs  with  oxalate  of  iron  in  the  presence  of 
a  salt  of  yttria,  under  peculiar  circumstances,  was  found  on  close 
examination  to  be  in  perfect  accordance  with  the  principles  laid 
down  by  Berthollet.  Besides  the  argument  founded  on  this  uni- 
versal fact,  several  experiments  were  devised  for  the  purpose  of 
proving  that  the  complete  precipitation  of  an  insoluble  salt  on 
the  mixing  of  two  soluble  salts,  was  due  to  the  insoluble  com- 
pound being  removed  at  once  out  of  the  field  of  action  on  the 
first  distribution  of  the  elements,  thus  necessitating  a  redivision, 
and  so  on  until  no  more  of  it  could  possibly  be  formed.  The 
phenomena  attending  volatilization  have  the  same  bearing  as 
those  connected  with  precipitation.  If  by  the  mutual  action  of 
two  salts  a  substance  be  formed,  which,  though  soluble  in  water, 
requires  more  water  for  its  solution  than  is  present,  it  crystallizes 
out ;  certain  experiments  were  noted  where  this  action  occurs, 
