176 



Magnesia, 5.4 4.3 6.3 15.9 5.1 



Chlorine, 2.7 2.9 2.6 0.0 0.6 



Carbonic acid, ...13.4 14.0 26.0 0.0 0.0 



Sulph. acid, 1.1 10.9 2.5 1.0 1.0 



Phosp. acid, 11.3 6.1 6.3 47.0 3.1 



Water and loss,.. 0.1 5.5 0.0 2.4 3.7 



100.00 100.00 100.00 100.00 100.00 



From these tables it is apparent that potash predominates in the 

 composition of the potatoe; that turnips are principally composed of 

 potash, lime, carbonic and sulphuric acids; that clover principally con- 

 sists of potash, lime and carbonic acid, whilst the grain of wheat is in 

 a great measure composed of phosphoric acid and potash, and the 

 straw of silica. A continuation of these agricultural tables would oc- 

 cupy too much room. It will be sufficient to mention the principal in- 

 gredients of the ashes of some of the most useful plants. Peas are 

 found to consist in a great part, of potash and phosphate of lime ; the 

 grain of rye, of phosphate of lime and potash ; the straw of rye, of 

 potash and silica. M. Sprengel found potash, soda and silica, to be the 

 principal ingredients in the grain of maize, and the straw to consist 

 chiefly of silica and lime. Liebig classes maize among those plants 

 which require but little potash in their formation ; yet it is clear that 

 •this plant varies much according to the soil in which it is grown, and 

 the analysis of several chemists go to show that it is not deficient in 

 that mineral. 



Every farmer should be thoroughly acquainted with the composition 

 of the plants he cultivates, the soil he grows them in, and the manure 

 he applies in order to render that soil fertile. When the structure and 

 composition of plants are understood, it will be plainly seen that they 

 deprive the soil of a certain portion of its ingredients, and that if they 

 are too frequently grown, they will entirely exhaust the soil of these 

 substances, and render it barren, and consequently incapable of produc- 

 ing a crop of the same kind as that which has absorbed so much of its 

 fertility. Experience has shown that after a soil is completely exhaus- 

 ted of these substances, which are necessary for the growth of one kind 

 of kind of crop, a change may be made, and the soil may be found ca- 

 pable of producing a crop of a different description ; and this fact is of 



