510 
ON  WHITE  GUMPOWDER 
does  its  color  vary  from  blue  ;  with  an  increase  of  the  organic 
substance,  the  color  gradually  passes  into  green,  yellow  and 
brown,  the  blue  being  gradually  obscured. 
7.  Every  water  meets  with  a  considerable  portion  of  one  agent 
changing  the  color,  namely,  humic  acid,  v/hile  the  other  agent, 
the  alkali,  is  distributed  in  very  variable  degree ;  the  color  of 
waters  poor  in  free  alkali,  therefore,  approach  blue  most  closely; 
an  increase  of  the  alkali  causes  an  increase  of  humic  acid,  and 
consequently  a  change  of  color  into  green,  yellow  and  brown. 
8.  It  follows,  then,  that  the  nature  of  the  rocks,  over  which 
the  water  flows,  furnishes  the  principal  condition  for  the  color 
of  water. 
9.  Periodical  changes  of  the  color  of  the  same  water  are  not 
caused  by  a  different  amount  of  organic  matter,  but  are  de- 
pendant on  atmospheric  conditions,  (cloudy  sky,  &c.) 
10.  As  a  general  rule,  waters  are  the  softer  the  more  they 
approach  the  brown,  and  the  harder  the  nearer  they  come  to  the 
blue  color.  The  cause  is  not  the  amount  of  organic  matter, 
but  the  amount  of  alkali  contained  in  solution,  on  the  latter 
of  which,  however,  depends  the  proportion  of  the  former. — 
(  Wittst,  V.  Schr.  X.  342-365.) 
WHITE  GUNPOWDER, 
Dr.  J.  J.  Pohl  has  improved  on  Augendre's  white  gunpowder 
{Sitzunsh.  du  AJcad.  der  Wissenschaft  zu  Wien.  Bd.  xli.  s, 
634].     He  prescribes  the  following  quantities  : 
Ferrocyanide  of  potassium       .       .        28  parts, 
Gane  sugar     .       .       .       .       ,       23  «« 
Chlorate  of  potash         .       .       ,       49  " 
100 
which  give  a  well-burning  powder,  and  nearly  approaches  the 
proportions 
K,FeCy3,3HO-|-C,2HiiOi,+3(KO  01,05). 
The  results  of  the  combustion  of  this  mixture  he  calculates' 
