CHEMICAL  NOTES. 
523 
are  easily  rubbed  into  powder,  and  thereby  show  a  marked  dif- 
ference from  the  fibres,  although  the  composition  of  the  salt  is 
in  both  instances  alike  =NH4  CI.  Chloride  of  potassium^  K  CI, 
likewise  contains  no  water  of  crystallization  when  crystallized 
in  either  form. 
For  the  above  reasons  I  consider  both  chlorides  dimorphous, 
each  crystallizing  in  the  regular  and  the  rectangular  system,  and 
isomorphous  in  both  forms.  But  the  difference  between  the 
two  consists  in  the  temperature  at  which  the  crystallization  takes 
place ;  chloride  of  potassium  crystallizes  from  a  concentrated 
solution  on  and  a  ter  cooling  in  prisms,  while  chloride  of  ammo- 
nium forms  under  the  same  circumstances  cubes ;  at  a  higher 
temperature,  when  sublimed,  the  latter  condenses  in  prisms 
while  chloride  of  potassium  is  deposited  from  a  hot,  concentrated 
solution  in  cubes. 
Acetate  of  Ammonia. — The  Pharmacopoeia  orders  the  solution 
of  this  salt  to  be  prepared  by  neutralizing  diluted  acetic  acid 
with  carbonate  of  ammonia.  It  is  not  very  easy  to  arrive  in  this 
way  at  a  precisely  neutral  liquid  ;  test  paper  is  of  no  avail,  in- 
asmuch as  the  solution  shows  an  acid  reaction  even  in  the  presence 
of  a  not  inconsiderable  amount  of  carbonate  of  ammonia,  on  ac- 
count of  the  carbonic  acid  gas  which  is  retained  by  the  liquid. 
Constant  agitation  in  a  mortar  will  expel  most  of  it,  but  if  an 
excess  of  carbonate  of  ammonia  was  present,  some  bicarbonate 
will  have  been  formed,  which  is  entirely  different  in  taste  from 
the  sesqui-  and  monocarbonate.  To  avoid  an  excess  of  ammonia, 
the  solution  is  generally  left  slightly  acid ;  but  a  better  way 
would  be  to  heat  the  diluted  acetic  acid  to  about  180°,  and 
neutralize  it  at  that  temperature  with  the  powdered  carbonate. 
A  still  easier  method  is  to  effect  the  neutralization  with  caustic 
ammonia,  as  is  directed  by  most  of  the  European  Pharmaco- 
poeias. One  measure  of  acetic  acid  may  be  diluted  with  three 
measures  of  water,  neutralized  with  ammonia,  and  then  diluted 
with  water,  so  as  to  make  altogether  eight  parts.  Thus  with  a 
strip  of  blue  litmus  and  of  turmeric  paper,  the  precise  point  of 
neutralization  may  be  easily  determined. 
Separation  of  Iron  from  sulphate  of  Copper. — Sesquioxide  of 
iron  is  precipitated  from  its  solutions  when  boiled  with  acetate 
