156 
ON  DECOLORIZING  CHARCOALS. 
The  propriety  of  this  classification  may  be  made  very  plain  by 
a  simple  experiment.  If  equal  quantities  of  purified  animal  or 
coal-tar  charcoal,  aluminized  charcoal,  and  bone-black,  are 
boiled  in  decoctions  of  logwood  till  they  are  saturated  with 
coloring  matter,  and  if  they  are  then  thrown  upon  filters,  which 
are  washed  with  dilute  solutions  of  aqua  ammonia,  the  ammoniacal 
solution  from  the  aluminized  charcoal  will  be  of  a  straw,  yellow 
color ;  that  from  the  bone-black  will  be  somewhat  deeper  ; 
while  those  from  the  purified  animal  and  coal-tar  charcoals  will 
be  nearly  as  deep  as  ink.  This  evidently  shows,  that  in  the  case 
of  the  aluminized  charcoal,  the  coloring  matter  was  in  true 
chemical  combination  with  the  alumina.  In  the  bone-black,  this 
was  also  partially  the  case,  while  in  the  purified  animal  charcoal, 
no  true  chemical  combination  had  been  formed,  but  the  coloring 
matter  was  merely  retained  by  the  porosity  of  the  charcoal. 
I  shall  conclude  this  paper  by  shortly  noticing  some  experi- 
ments on  the  power  which  the  various  decolorizing  charcoals 
possess  of  absorbing  three  of  the  gases,  viz.,  ammonia,  carbonic 
and  hydrochloric  acids.  Their  results,  which  are  somewhat 
anomalous,  I  have  thrown  into  the  subjoined  tabular  form.  A 
gramme  of  each  charcoal  was  employed.  All  the  charcoals  were 
decolorizers,  except  the  platinized  charcoal,  which,  as  it  consists 
of  common  wood  charcoal,  impregnated  with  a  small  quantity 
of  metallic  platinum,  of  course  possesses  no  affinity  for  color- 
ing matters, 
Cubic  centimetres  of  Gases  absorbed  by  one  gramme  of  various  hinds  of 
Charcoals. 
NAME  OF  CHARCOAL. 
NAME  OF  GAS. 
Ammonia. 
Carbonic  acid. 
Hydrochloric 
acid. 
145 
105 
210 
212.5 
152.5 
335 
142.5 
15 
2.5 
No  Absorption. 
12.5 
10 
No  absorption. 
No  absorption. 
158.7 
Not  tried. 
185 
177.5 
Not  tried. 
130 
135 
7J  percent.  Aluminized  
7  J  per  cent.  Phosphate  of  Lime 
In  connexion  with  the  absorbent  power  of  charcoal  for  gases, 
I  may  mention  that  the  charcoal  air-filters,  respirators,  and 
