On the Camcs of the Efficacy of Burnt Clay. 



497 



But in order that a chemist may be successful, it is most essential 

 that he should possess sufficient knowledge ()f a practical kind 

 to enable him to investigate a chemico- agricultural question in 

 all its bearings, or that he should avail himself of the aid which 

 practical men will afford him. 



The practice of soil-burning has long since been recommended 

 by different persons as one of the best means of improving stiff 

 clav land^ whilst others denied the utility of soil-burning altOLzether. 

 But althou.orh failures sometimes attended this practice, we are 

 now in possession of numerous incontrovertible instances in which 

 the application of burnt clay was followed bv the happiest results. 

 One of the most striking examples in which soil-burning proved 

 highly economical is recorded in volume vi. page 477 of this 

 Journal by Mr. Pusey, who very justly observes that burnt clay 

 acts, not merely mechanicall v. but also as a manure (that is 

 chemically). 



The failures attending clav-burning no doubt are due in some 

 cases to carelessness and want of skill on the part of the operator, 

 for it is well known that in over-burning soil, instead oi a triable 

 mass, largfe hard lumps like brickbats are obtained, which on 

 exposure to the atmosphere refuse to fall to powder. Soil burnt 

 at too high a temperature, that is overburnt soil, always proves 

 more or less inefficient. All failures, however, cannot be attri- 

 buted to this cause, for it is a fact, attested by practical men 

 well acquainted with the practice of soil-burning, that some kinds 

 of clay after burning do not exhibit the same beneficial effects as 

 others, or none at all when applied to the land. It becomes, 

 therefore, an important point to determine what is the nature of 

 those clays which prove efficacious after burning, and what are 

 the characteristics of those clays which are unfit for burning. 

 It is clear, however, that this question cannot be settled satisfac- 

 torily without incurring much expense, as long as we are ignorant 

 of the true cause of the efficacy of burnt clay. In addition to 

 other advantages, the discovery of the cause of the efficacy of 

 burnt clay further might probably lead to improvements in the 

 existinc^ methods of burnins: clav, which nii":ht render them 

 easier, cheaper, and more certain. 



These and similar considerations, I think, will show at once 

 the practical importance of a fundamental inquiry into the causes 

 of the efficacy of burnt clay. 



With a view of contributing something to the solution of the 

 problem, I made some experiments last winter which have fur- 

 nished me with some interesting analytical results. These, I 

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

 lead at the same time to a m^ore extensive practice of burning 

 heavy clay land. 



VOL. XEI. 2 K 



