during the last Four Years. 213 



not at all better than when it is slacked.* Dr. Liebig has 

 recently discovered that lime has the power of decomposing clay, 

 and producing potash and soda, which are manuring principles : 

 now if this be the mode in which lime acts, there could 

 not be a better course than to mix lime with earth before it is 

 thrown upon grass-land, and the old practice would agree with 

 the true theory, as is often the case. Of all things we must guard 

 against premature inferences from abstract science ; but be the 

 cause what it may, the effect of lime in sweetening sour pastures 

 is wonderful throughout the districts where it is used, and it is 

 well worth inquiry whether it could be applied in those districts 

 where it is at present unknown. 



We have then several substances more or less simple which pro- 

 duce the effect of dung. The mode of their action belongs not 

 to the practice, but to the theory, of agriculture, into which I am 

 not competent to enter ; but as important discoveries have lately 

 been made in that department, I will endeavour to state the 

 modern German Theory as founded by Sprengel, and lately 

 established by Dr. Liebig. 



Plants consist in the main of several vegetable substances, 

 which are, however, all composed oifour kinds of air variously com- 

 bined ; these gases are named Oxygen, Hydrogen, Carbon, and 

 Nitrogen. Dr. Liebig supposes that the two first are derived by 

 the plant from water ; the third, which is charcoal, from the air ; 

 and the fourth, nitrogen, which constitutes the most nutritious 

 part of our food, from ammonia : which substance he has found 

 not merely in the dung of animals, but in the water of rain, a new 

 and remarkable fact. But there exists also in crops a consider- 

 able quantity of earthy matter ; in every ton of oat- straw, for 

 instance, nearly one cvvt. of flint, whence, if a hayrick be burnt 

 lumps of a substance like glass are often found in the ashes. 

 These mineral substances vary in different plants as to quantity, 

 but eight are generally to be found in their ashes, four of the 

 eight being Acids, namely, that of flint, which is Silica ; of bones. 

 Phosphorus; of brimstone. Sulphuric acid; of common salt. Muri- 

 atic acid : and also four Alkalis, Potash, Soda, Lime, and 

 Magnesia. f These, Dr. Liebig says, cannot of course be formed 



* On the other hand, at Woburn, I have just met with a case in favour 

 of recent Ume, The soil was a Hght sand with a tendency to blackness at 

 top : half a turnip-fiekl had been dressed with fresh, and half with slacked 

 lime, and there was a marked difference in favour of the fresh lime. As far as 

 our knowledge goes, which is not far, lime appears to me to act wherever 

 there is a natural tendency in the soil to cover itself with heath on waste 

 places, and also wherever the soil is of a deep red, which colour indicates a 

 peculiar salt of iron. 



f A very small quantity of alumine, or the earth of clay, is also usually de- 

 tected in the ashes of plants. 



