214 Progress of jlgricultural Knoulccuje 



in the plant, but inust be derived from the soil ; and accordingly 

 there they are g-enerally to be found when the soil is examined 

 by chemists, but in limited quantity, so that the soil may become 

 exhausted of one or more of them. But further, all these 

 eight mineral substances are to be found in farm-yard dung, 

 besides ammonia, the source of nitrogen: hence the excellence 

 of dung for all crops indifferently. Some crops, however, 

 require more of one ingredient than of another : hence the 

 good effect of bones upon turnips, which contain a great 

 deal of phosphorus, and of gypsum or peat-ashes, which con- 

 tain sulphate of lime, upon clover ; of Epsom salts also. Dr. 

 Liebig states, which contains magnesia, upon potatoes. Some 

 soils, again, may contain so much of one of these eight mi- 

 nerals, that it may be useless to add any more. Thus gypsum 

 is found to be useful in one part of a field and not in another, 

 and bones are useless in Mecklenburg, where the fields are 

 dressed with a marl full of phosphorus ; or, on the other hand, 

 a tract of country may be deficient altogether in some one of 

 the eight ingredients which is necessary for all crops, as in 

 lime : in such a district lime will be a standing manure. This 

 is a very superficial view of the new theory of agriculture, 

 which, though but a theory at present, certainly promises im- 

 portant results. In order to test it first, and, if it hold good, to 

 apply it afterwards, two courses of inquiry are requisite — one, 

 as Dr. Liebig informs me, a more minute examination of the 

 ashes of plants, in which these mineral substances are found, and 

 further a more accurate analysis of our various soils, in which 

 last particular English science is sadly defective : for Dr. Liebig 

 observes, " Davy has made several analyses of various fertile 

 soils, and since his time numerous other analyses have been 

 published, but they are all so superficial, and in most cases so 

 inaccurate, that we possess no means of ascertaining the composi- 

 tion or nature of English arable land." This reproach on our 

 science ought certainly to be removed ; and it is easy to see how 

 varied a field of inquiry is opened by the new theory. At the 

 same time, though it is a most promising theory, it would be pre- 

 mature to expect that for some years to come chemistry should be 

 able to direct, or materially to benefit, actual husbandry. But 

 though we have not yet seen the secret workings of nature, I be- 

 lieve that we are near the door, and that the veil will soon be 

 raised. Any young chemist, who will take up the late brilliant 

 discoveries of general principles and devote his life to patient 

 research into the means of applying them, may hope to acquire 

 an imperishable reputation; and it is evident, from the ardour 

 with which chemists now embark in agricultural research, that 

 they feel they are making progress. But we certainly have to 



