242 
THE  SOAP-BARK  OF  SOUTH  AMERICA. 
clear  water.  There  is,  however,  no  separation  of  the  constituents 
of  the  oil,  as  is  the  case  by  the  reaction  of  alkaline  substances. 
Alcohol  does  separate  the  emulsion,  the  oil  is  restored,  and 
a  white  granular  substance  subsides. 
The  extract  mentioned,  has  the  property  of  reducing  gold 
from  its  chloride  ;  the  glass  employed  for  the  experiment  will  be 
beautifully  gilded ;  the  reduction  is  much  accelerated  by  the  in- 
fluence of  the  direct  rays  of  the  sun.  The  same  power  of  reduc- 
tion is  shown,  by  mixing  the  extract  with  the  alkaline  copper 
solution  as  prepared  by  Fahling  for  the  quantitative  sugar-proof ; 
the  reduction  into  the  red  oxide  of  copper  immediately  follows 
on  the  application  of  heat.  That  this  reduction  is  not  produced 
by  the  presence  of  a  sugar-like  substance  or  glucose,  is  demon- 
strated by  the  experiment  of  Boettger  with  the  basic  nitrate  of 
bismuth,  for  when  this  is  boiled  with  the  extract  of  the  bark  it 
remains  white,  which  does  not  happen  when  there  is  glucose 
present  in  the  smallest  quantity.  The  solution  of  mineral 
chameleon  is  immediately  changed  from  green  to  light  yellow. 
I  have  observed  that  the  mucilaginous  extracts  made  with 
water  at  a  low  temperature,  by  macerating  the  roots  of  the 
marshmallow  ( Althcea  officinalis,)  of  the  comfrey  (Symphytum,) 
and  of  the  grains  of  the  quince,  have  not  the  same  influence  on 
chloride  of  gold.  The  extracts  of  these  roots  precipitate  the 
gold,  under  the  form  of  the  purple  of  Cassius,  only  at  a  boiling 
temperature ;  the  mucilage  of  the  grains  of  quince,  however, 
likewise  at  ordinary  temperatures,  produces  a  precipitate  having 
the  lustre  of  metallic  gold.  The  reduction  of  the  copper,  as 
mentioned  above,  will  not  happen.  These  mucilages  have  like- 
wise the  property  of  forming  emulsions,  but  weaker  and  not  so 
lasting. 
The  extract  of  the  soap-bark  is  colored  a  reddish  brown  by 
nitrate  of  silver,  and  ammonia  forms  a  precipitate.  When  a 
proper  proportion  of  nitrate  of  silver  with  ammonia  is  prepared, 
a  silver  lustre,  like  that  of  the  silvering  of  glass,  will  be  produced 
by  heat. 
Concentrated  sulphuric  and  nitric  acids  produce,  by  boiling, 
a  sediment  in  the  form  of  white  flocks  ;  the  white  flocks  produced 
by  the  reaction  of  sulphuric  acid  are  colored  brown  by  iodine. 
The  experiments  with  other  chemical  re-agents  have  not  pro- 
