Outlines of Horticultural Chemistry. 129 



predominate in its constitution, a soil rakes best just after it 

 has been turned up witii the spade. If clay does predominate, 

 it usually rakes with most facihty after it has been dug two or 

 three days, and then immediately after a gentle rain. But it 

 is certain that the sooner seed is sown after the soil is dug for 

 its reception, the earlier it germinates. In the droughts of 

 summer, water is often required to newly sown beds. Such 

 application must not be very limited or transitory ; for, if the 

 soil is only moistened at the immediate time of sowing, it in- 

 duces the projection of the radicle, which, in very parching 

 weather, and in clayey caking soil, I have known wither 

 away, and the crop be consequently lost from the want of a 

 continued supply of moisture. 



From the slight sketch contained in the foregoing papers, it 

 will have been seen that plants derive their whole nourish- 

 ment from the air and soil. It is of importance to know how 

 the constituents of these may be ascertained, so as to enable 

 us to judge beforehand whether they hold out a prospect of 

 affording a plentiful increase to the cultivator. 



Experiments on the constituents of atmospheric an*, are 

 never required by the tiller of the ground ; for it has been de- 

 monstrated by the best chemists that its composition is inva- 

 riably the same in all parts of the globe, and whether obtained 

 from a level with the sea, or from the greatest height to which 

 man has found means to ascend. Their researches afford one 

 general result, which is, that the atmosphere is composed of 

 21 parts oxygen, and 79 parts nitrogen, with the admixture 

 of about 1 part of carbonic acid gas in every 1000 of its 

 parts. 



This simplicity of composition is very far from existing in 

 soils ; of them, perhaps, no two specimens in the world are 

 precisely alike. 



Before I proceed to detail the mode of analysing a soil which 

 I employ, and for which mode I was originally indebted to the 

 Elements of Experimental Chemistry by Dr. Henry, I must 

 pause to animadvert upon two common prejudices, each of 

 them the offspring of ignorance. 



The first prejudice is that which argues that chemistry is of 

 no use to the cultivator of the soil. I slightly touched upon 

 this in my opening paper, and the effect of Lavoisier's prac- 

 tice, directed as it was by science, is an incontrovertible argu- 

 ment against this prejudice, for facts are not to be overturned 

 by obstinacy ; but I am induced to argue the point more in detail, 

 by having heard such an objection raised by a person whom I 

 have been accustomed to consider possessed of a liberal mind. 



Vol. v. — No. 19. k 



