my theory respecting the liberation of potash in clay, are the 

 first direct proofs which have been furnished by any chemist. 

 Though unacquainted with Professor Zieifs theory, and Professor 

 Fuchs' experiments, when I undertook the investigation, I am 

 bound to acknowledge that the theory I have embraced, respect- 

 ing the liberation of potash in clay, is not a new one. Disclaiming 

 the merit of being its discoverer, I shall feel amply rewarded by 

 seeing these direct experimental proofs in support of this theory 

 confirmed by the experience of other chemists. 



4. Is it essential, or desirable, that clays fit for burning should 

 contain lime ? 



My own experiments have been confined to clay which con- 

 tained originally lime ; I am, therefore, not prepared to answer 

 the first part of the question namely, is it essential that clays fit 

 for burning should contain lime ? The observations already 

 made respecting the action of lime on insoluble silicates of 

 potash and soda, however, enable me to answer the second part of 

 the question namely, is it desirable that such clays should contain 

 lime V in the affirmative. If the above explanation of the action of 

 lime on silicate of potash is true, we can easily conceive how the 

 addition of lime to clay, originally poor in this element, will 

 increase the amount of soluble potash and soda. In this view of 

 the matter I am much confirmed by an observation of Professor 

 Fuchs of Munich, to which particular interest attaches. This 

 eminent man, distinguished both as a good chemist and mineral- 

 ogist, found that when felspar is moderately calcined, and in a 

 powdered state is boiled with quick-lime and water for a short 

 time or even digested in the cold with quick-lime and water for a 

 longer period so large a proportion of potash is liberated from the 

 constituents of felspar that, on these grounds, he recommended a 

 process of extracting and manufacturing potash on a large scale 

 from felspar. Professor Fuchs has shown that, under these cir- 

 cumstances, insoluble silicate of lime and soluble carbonate of 

 potash are formed. I would, therefore, suggest the application of 

 quick-lime to newly burnt clay land, or the mixing of clay with lime 

 before burning, as likely to be attended with most beneficial effects. 



5. What are the characteristics of clays, of which it can be said 

 that they are totally unfit for burning ? 



The chief mass of all clays, silicate of alumina, does not in itself 

 serve as direct food to plants. Pure clays, such as pipe and 

 porcelain clay, which almost entirely consist of silica and alumina, 

 for this reason will be found as sterile after burning as they are 

 in their natural state. We have seen that the accessary constituents 

 of agricultural clays furnish the materials from which plants derive 

 inorganic food. Of these the most important and valuable are 

 phosphoric acid and the alkalies. As phosphoric acid is riot ren- 

 dered more soluble in burning clay, but rather the contrary, as 



