208 On the Physical Properties of Soil 



moisture and of oxide of iron, which are found in all the clays, 

 appears to be the principle of this phenomenon. 



Power of exciting Electricity. — All the earths develope ne- 

 gative electricity when oblong dry pieces of them are scraped 

 with a knife, and the resulting particles immediately received on 

 the plate of an electrometer ; the voltaic straw-stalk electrometer, 

 by this manipulation, generally exhibits divergences of from 4 to 

 5 degrees : ice treated in the same manner gives positive elec- 

 tricity. 



Polar-electric Relation. — When solutions of humus in alkalis 

 and earths (the humic acid salts) are exposed to the current of the 

 voltaic battery, decomposition immediately ensues; the humus, 

 or peculiar humic acid, collects in brown flakes around the posi- 

 tive or zinc end of the apparatus, while the earths or alkalis 



arrange themselves around the copper or negative end of the 

 polar wire ; humus, therefore, assumes in relation to the remain- 

 ing earths the character of an acid, a circumstance which I 

 pointed out, when I first made the experiment in the year 1817, 

 in the fifth part of the Agricultural Journal of Hofwyl. 



Influence of the simple Earths on the Germination of Seeds. — 

 When we allow grain to germinate in the simpler earths, the 

 young plants will, for some time, develope themselves as long as 

 the earths possess the proper looseness and also remain suffi- 

 ciently moist and at a proper temperature ; conditions, which, ac- 

 cording to what has been already said, on the capability of earths 

 to become dry, must occur in different degrees ; independently, 

 also, of the moisture and warmth, the consistence of the earths 

 has a great influence on the development of the germ ; for if 

 they have too great a consistence, the seeds lie in them without 

 growing. 



The several earths, in my investigations, exhibit the following 

 differences in this respect : — 



In moist siliceous and calcareous sand, the grains germinated 

 in summer in a few days, and developed themselves well for some 

 time, but suffered on the approach of hot weather. 



In gypsum powder, the young plants became developed but in- 

 differently ; from the alternation of moisture and dryness, a crust 



