in various parts of the country for the purpose of supplying far- 

 mers, at a cheap rate, with properly burnt and finely powdered 

 clay. 



The crops which were benefited most by the application of burnt 

 clay, next to potatoes, were ascertained by Lampadius to be peas, kohl- 

 rabi, carrots, beetroot, clover, oats, rye, and wheat. Less favour- 

 able he found its use as a top-dressing for pasture land. It is 

 worthy of remark that the good effects of burnt clay were observed 

 on beans, kohl-rabi, and carrots, after the third year, without re- 

 ceiving any additional manure. 



Having thus shown on what grounds Lampadius recommended 

 the more general use of burnt clay, we shall now endeavour to 

 collect from his extensive papers the theories he advanced to 

 account for these extraordinary and interesting effects. 



At first he appears to be inclined to ascribe to humate of alumina, 

 which according to him is formed in the soil, a highly beneficial 

 action on vegetation, and hints that burnt clay would fail in its 

 effects when the soil was exhausted of humus ; but having soon 

 after found that burnt clay in soil destitute of humus produced, 

 nevertheless, unmistakeable effects, he soon gave up this theory, 

 and next explained the effect, by saying that clay in burning 

 undergoes some peculiar unexplained changes, by which changes 

 the manuring substances in clay are rendered available to plants. 

 It will be observed that this explanation amounts to little more 

 than stating the fact in other terms. Indeed, the modified and 

 varied opinions Lampadius entertained afterwards on this subject 

 clearly show how little satisfied he was with this theory. As the 



?robable causes of the effects of burnt clay, he mentions in 

 833 : 



a. The changes in the state of aggregation clay undergoes in burning. 



b. The decomposition of the hydrates occurring in clay. 



c. The changes which the earthy substances of the clay undergo in burning, which 



changes render them more soluble in the humic acids of the soil. 



d. The higher state of oxidation of the oxides of iron and manganese produced 



in burning clay. 



e. The production of a larger quantity of soluble sulphates, phosphates, and hydro- 



chlorates, which, previous to burning, occur in a more fixed state in clay. 

 /. The absorption of light and heat by burnt clay. 

 g. According to Dr Sprengel, the formation of ammonia in burnt clay. 



Several of these opinions were abandoned by Lampadius, who, 

 in 1834, ascribes the effects of burnt clay to the following 

 causes : 



(1.) To the inorganic constituent parts of unburnt and burnt clay, which are 

 essential to the growth of cultivated plants. 



(2.) These constituents are rendered more soluble, in various ways, in moderately 

 burnt clay. Unburnt clay gave 0.20 soluble matters; moderately burnt clay, 

 0.30 soluble salts. Humic acid dissolves likewise silicate of alumina, and 

 the other constituents of clay, more readily when clay has been previously 

 burnt. 



(3.) The protoxide of iron in the clay takes up more oxygen in burning, and be- 

 comes converted into peroxide, which, according to Sprengel, acts beneficially 



