76 
ON  CHLORAL. 
chloral  put  into  a  moist  flask  deposits  star-shaped  crystals  of  the 
hydrate  on  the  sides.  The  aqueous  solution  of  chloral  is  indif- 
ferent to  vegetable  colors  ;  oxides  of  silver  or  mercury  have  no 
effect  upon  it ;  concentrated  sulphuric  acid  deprives  it  of  water 
and  separates  the  anhydrous  crystals. 
One  of  its  most  remarkable  properties  is  the  change  it  un- 
dergoes spontaneously  when  kept ;  it  is  altered  into  a  porcelain- 
like mass  called  metachloral,  which  is  insoluble,  though  isomeric 
with  the  liquid  form.  It  can  be  reconverted  into  chloral  by  dis- 
tillation. The  white  metachloral  is  insoluble  in  alcohol  and 
ether,  as  well  as  in  water,  but  by  contact  with  water  it  is  grad- 
ually converted  into  the  crystallized  hydrate  of  chloral. 
Fuming  nitric  acid  changes  chloral  into  tri-chloracetic  acid. 
An  alcoholic  solution  of  potash  converts  chloral  immediately  into 
formiate  of  potash  and  chloroform.  This  reaction  may  be  rep- 
resented as  follows,  C^CPHO-l-KHO-^KCHO^+CHCP.  For 
pharmaceutical  purposes  chloral  hydrate  must  form  a  hard, 
white,  crystalline  mass,  be  completely  soluble  in  water,  not 
smell  of  chloride  of  carbon  or  hydrochloric  acid,  but  retain  the 
peculiar,  penetrating  odor  characteristic  of  chloral.  It  would 
be  dangerous  to  employ  hydrate  of  chloral,  contaminated  by 
chlorous  acetylene,  chloride  of  carbon  and  other  incidental  pro- 
ducts, and  hence  great  care  must  be  observed  in  its  preparation. 
Much  attention  has  recently  been  called  to  the  hydrate  of 
chloral  in  consequence  of  the  physiological  researches  of  Dr. 
Liebreich.  This  gentlemen,  in  presenting  his  paper  to  the 
Chemical  Society  of  Berlin,  May  24,  1869,  gave  the  following 
interesting  explanation  of  the  occasion  of  his  research  : 
"  There  are  some  substances  which  pass  through  the  body  without 
decomposition  and  without  exercising  any  appreciable  influence 
on  the  even  tenor  of  our  life ;  there  are  others  which  go  to  build 
up  and  nourish  ;  others  take  up  something  from  the  body  by 
chemical  decomposition  and  then  leave  it ;  some  are  useful,  such 
as  acetic  acid  and  sugar.  I  experimented  recently  to  ascertain 
if,  by  the  splitting  up  of  certain  compounds  in  the  body,  the 
separated  compound  would  exert  the  same  influence  it  would  if 
administered  alone. 
Trichloracetic  acid  of  Dumas  and  chloral  of  Liebig  appeared 
