ON THE CHEMICAL CONSTITUENTS OF SOILS. 213 



render unnecessary the animal manures, which act 

 by their inorganic ingredients. According to Ber- 

 thier, 100 parts of the ashes of wheat straw con- 

 tain, — 



Of matter soluble in water 9*0 



Of matter insoluble in water . . . . 91-0 



Now 100 parts of the soluble matter contain, — 



Carbonic acid ...... a trace 



Sulphuric acid 20 



Muriatic acid 130 



Silica . , . 350 



Potash and Soda 500 



1000 



100 parts of the insoluble matter contain, — 



Carbonic acid . . , . .0 



Phosphoric acid . . , . .1*2 



Silica 75 



Lime ...... 58 



Oxide of Iron and Charcoal .... 10-0 



Potash ...... 8-0 



100-0 



The silicate of potash employed in the preparation 

 of the compost described above must not deliquesce 

 on exposure to the air, but must give a gelatinous 

 consistence to the water in which it is dissolved, and 

 dry to a w^hite powder by exposure. It is only at- 

 tractive of moisture when an excess of potash is 

 present, which is apt to exert an injurious influence 

 upon the tender roots of plants. In those cases 

 where silicate of potash cannot be procured, a suffi- 

 ciency of wood ashes will supply its place.* 



All culinary vegetables, but particularly the cruci- 



* In some parts of the grand duchy of Hesse, where wood is scarce 

 and dear, it is customary for the common people to club together and 

 build baking ovens, which are heated with straw instead of wood. The 

 ashes of this straw are carefully collected and sold every year at very 

 high prices. The farmers there have found by experience that the 

 ashes of straw form the very best manure for wheat; although it exerts 

 no influence on the growth of fallow-crops (potatoes or the leguminosaB, 

 for example). The stem of whept grown in this way possesses an un- 

 common strength. The cause of the favorable action of these ashes 

 will be apparent, when it is considered that all corn plants require sili- 

 cate of potash ; and that the ashes of straw consist almost entirely of 

 this compound. — Ed. 



