402 ORGANIC CHEMISTRY. 



pression. On subsequently introducing the goods into 

 the madder bath, the various colors are developed. The 

 whole piece is at the same time transiently colored ; 

 but the dye may be readily removed from the imprinted 

 portion by thorough washing. A white ground for the 

 colors is thus obtained. 



RELATION OF PLANTS TO THE SOIL. 



AGRICULTURAL CHEMISTRY. 



1008. The mineral substances which 



What mineral , , _, . ,. . ., , , 



substances do plants obtain from the soil, are known by 

 plants obtain ana iy s i s o f the ashes which they yield on 



from the soil ? J J 



combustion. They consist of acids and 

 bases, which enter into the composition of all fertile 

 soils. The bases are potassa, lime, magnesia, and 

 oxides of manganese and iron. These are found com- 

 bined in the ashes with silicic, sulphuric and phosphoric 

 acids, and are accompanied by small proportions of 

 common salt. The carbonic acid which is found in 

 certain ashes is produced in the combustion of the 

 plant. The ashes of all cultivated plants contain the 

 above substances ; but in different proportions accord- 

 ing to the nature of the plant. The phosphates pre- 

 dominate in grains ; lime exists in large proportion in 

 grasses ; potash in edible roots ; and silica in straw. The 

 approximate composition of the ash of different plants 

 is given in a table in the Appendix. In estimating the 

 relative proportions of the different constituents which 

 are abstracted from the soil by different crops, the quan- 

 tity of the crop, as well as the composition of its ash, 

 is of course to be brought into this account. 



