192 



of tlie sand-samples and tlie mostly l»lne to hliiisli-hlack coloiii- of 

 tlie clay-sampies points to prevailing sulphate-reduction. This com- 



mences at about 10 m. below the surface (7.5 m. — A. P.)') to ± 

 37 m. (34.50 m. — A. P.) the largest depth examined here. 



The conditions under which sulphate-reduction appears are: 



1°. Absence of oxygen '). 



2'. The occurrence of organic compounds. 



3'. The presence of sulphate and the required mineral compounds. 



The first condition, the absence of oxygen, is satistied in conse- 

 quence of the considerable depth below the level of the ground. 



The second conditioi»: the occurrence of organic compounds, is 

 fulfilled already to the eye by the peat-sample and also by the 

 clay-sample with enclosed peat-layers. That the sand-, and clay- 

 samples, which do not enclose immediately distinguishable organic 

 particles, also contain organic matter, can be demonstrated chemically, 

 by the potassiumpermanganate method. This is conducted as follows : 

 The soil-sample is boiled with diluted sulphuric acid and tillered. 

 The fdtrate is cooled down under the tap; now potassiumpermanganate 

 (0.01 norm.) is instilled. The first di-ops are directly decolorized, 

 which is owing to the oxidation of ferro- and mangano-compounds, 



') The grounds of the wells at the Sprenkelkanaal is lying at 2.5 M. above A. P. 

 2) Traces of oxygen are left out of consideration here. 



