APPENDIX, XXXlll 



its internal surface to the frost; and for this reason the autumn 

 ploughing should be as deep as possible. The fertilizing prin- 

 ciple is unquestionably nitre, the materials for which we know 

 exist more or less in the air, as is proved by the ease with which 

 that salt is procured by lixiviating the earth under stables, 

 sheds, and tobacco houses, with water, and by evaporating it, 

 and purifying the salt thus obtained by repeated solutions in 

 water. No difficulty occurs in explaining the formation of 

 nitre, knowing as we do that " the component parts of nitrate 

 of potash are nitric acid, water, and potash, which may be re- 

 solved into the following elements: oxygen, nitrogen, hydrogen, 

 and potassium; and all these elements are experimentally 

 known to be present in the situations where salt petre is form- 

 ed, witli the exception of potassium. In the supposition that 

 the salt petre is a produet, and not an educt, of the above pro- 

 cess, it must be a component principle of some one of the ele- 

 ments present, or a compound of two or more of the principles 

 of those elements, or of two or more of the elements them- 

 selves."* 



The common objection I have heard urged against early 

 sowing, is the want of warmth in the ground, owing to which 

 the seed would not vegetate. But this is futile: for grain can- 

 not suffer from being in the ground, and will be ready for the 

 gradual increase of heat in the spring. Both oats and barley 

 will vegetate at a low degree of temperature. Even in the 

 cold climate of Scotland, "barley has been sown on the winter 

 furrow, as early as March, and never failed to produce an 

 abundant crop, and of a superior quality "f 



It should always however be held in mind, that barley re- 

 quires a deeper cover of mould, and more pulverised soil, than 

 oats. 



* Kid on the Natural Production of Salt Petre. Trans. Royal Soc. Lond. 

 1815. 



f Account of Husbandry in the improved districts of Scotland, by Sir 

 John Sinclair, p. 249. Edinb. 1812. 



E 



