have from time to time been advanced by agriculturists and 

 chemists. Even though such a high authority on agricultural 

 chemistry as that of Liebig had made us acquainted with a theory, 

 in explanation of these effects, it must be confessed and practical 

 men as well as agricultural chemists acknowledge that we have 

 still much to learn on the subject, before we can, with any amount 

 of probability, offer an explanation of these various effects. 



With a view of contributing something to the solution of the 

 problem, I made some experiments during last winter, which have 

 furnished me some interesting analytical results. These, I trust, 

 will throw some light on the rationale of clay-burning, and at the 

 same time show the importance of a more extensive practical 

 application of the process on heavy clay lands. 



Before submitting to the reader my own results, I shall take 

 a rapid survey of the history of the observations of others on the 

 subject. 



It has been mentioned already that burnt clay appears to have 

 been used as a manure long ago. Amongst those who recommended 

 it, Robert Sommerville, and particularly General Beatson, deserve 

 notice. The General, in his book entitled New System of Cultiva- 

 tion, without Manure, Lime, or Fallow, of which a second edition 

 appeared in 1821, mentions the names of Curwen, Boyd, Cart- 

 wright, Cray, and others, as observers of the beneficial effects of 

 burnt clay on vegetation, and strongly recommends the practice 

 of soil-burning, as one of the best means of improving land, 

 especially stiff heavy clay soil. The appearance of this work 

 created some sensation at the time amongst the agricultural com- 

 munity and the scientific public, both in this country and on the 

 Continent. It excited, indeed, the curiosity of German agricultural 

 chemists in a high degree, arid occupied the attention of several 

 eminent Continental philosophers, in a measure which was scarcely 

 equalled by the attention bestowed on the subject by the scientific 

 men of England. Sprengel, the celebrated German agricultural 

 chemist, Professor Hermbstadt, Professor Kastner, Professor 

 Zierl, Kersten, and, above all, Professor Lampadius, took up the 

 subject with much warmth, and each speculated, after his own 

 manner, on the causes of the alleged beneficial effects of burnt 

 clay. A short review of the labours of these distinguished men, 

 which by no means are so well known by the agricultural public 

 of Great Britain as they deserve, I trust will not be unacceptable 

 to the reader, if it were only for the purpose of demonstrating 

 how fallible the judgments of even great men are, and of incul- 

 cating the moral lesson so frequently forgotten by theoretical 

 writers, that theories should be put forward with the utmost 

 caution and modesty. How often do we find a favourite theory 

 offered to the public in a manner in which only a mathematical 

 truth, or a law of nature, confirmed by the experience and labours 

 of many generations, can be advanced, and, after all, the same 



