850 



HOW CROPS FEED. 



posable silicates. A number of analyses which illustratfl 

 these facts are subjoined : 



Water 



Orsranic matter 



Siiiui and insoluble silicates. 



(Clay, kaoliiiite) 



f Silica 



(jD , Oxide of iron 



£. Alumina 



g. ' Lime 



5- I Magnesia 



Potash 



Soda 



Phosiphoric acid 



Sulphuric acid 



Carbonic acid, clilorine, 

 ^ and loss 



Sandy Loam. 

 Heiden. 



1.613 

 2.387 

 89.754 

 (10.344) 

 2.630* 

 1.8-2 

 1.152 



o.ini 



0.201 

 0.242 

 0.034 

 0.083 

 0.007 



White 

 Clay. 



5. 



Porce- 

 lain 

 Vlay. 

 Rautenbekg. 



Bed 



Clay. 



6.15 

 none 

 58.03 



18.73 

 2.11 



12.15 

 0,27 

 0.29 

 0.86 

 1.41 



none 



.095 I 

 .(XW 1 



6.80 

 0.90 

 4.35 



89.46 

 0.04t 



0.12 

 0.08 



6. 



White 

 Pottery 



Clay. 

 Wat. 



6.18 

 none 

 58.72 



13.41 

 5.38 



13.90 

 0.61 

 0.43 



100.00 I100.20 lioo.oo 



• This soil yielded to solution of carbonate of soda before treatment with 

 acid, 0.340 "u silica. 

 + The eilica in this case is the small portion held in the acid solution. 



The first three analyses especially, show that the soils 

 to which they refer, contained a silicate or silicates in 

 which iron, alumina, lime, magnesia and the alkalies ex- 

 isted as bases. How much of such silicates may occur in 

 any given soil is impossible to decide in the present state 

 of our knowledge. In the soil, free silica, is usually, if not 

 always present, as may be shovvn by treatment with solu- 

 tion of carbonate of soda, but it appears difficult, if not 

 impossible, to ascertain its quantity. Again, hydratcd 

 oxide of iron (according to A. Miiller and Knop) and hy- 



li'ated alumina* (Knop) may also exist, as can be made 

 evident by digesthig the soil in solution of tartrate of 

 .■^oda and potash (Mtillcr, Ys. St , IV, p. 277), or in a mi.x- 

 ture of tartrate and oxalate of ammonia (Knop, Vs. St. 



VIII, p. 41). Finally, organic acids occur to some ex- 

 tent in insoluble combinations with iron, alumina, lime, 



• Jl'ire probably, highly basic carbonates, or mixtures of hydrates and car 

 bunates. 



