256 EFFECTS OF BURNED CLAY. 



phate of alumina present in the latter, or the state in which 

 this acid exists in the salt, has an appreciable influence. If 

 18 Jib. of unburned gypsum act differently from the same 

 weight of sulphate of potash, (p. 128,) then the presence of the 

 lime and the potash, respectively, may be regarded as modify- 

 ing the apparent effects of each. And if 74 Ib. of unburned 

 gypsum, which contain as much sulphuric acid as 100 Ib. of 

 alum, affect the crop or land differently from this weight of 

 alum, then it is not to the quantity of acid alone that the influence 

 of the alum is to be ascribed, but in part, also, to the state of 

 combination in which it exists, or to the substances with which 

 it is combined. In regard to these salts of alumina, it should 

 be particularly observed 



1. What effect they produce on the appearance, the quantity, 

 or the quality of our different crops. 



2. Have they any special influence, as other sulphates are 

 supposed to have, on leguminous crops? Do they more dis- 

 tinctly act upon cabbage, onions, &c., than upon other culti- 

 vated plants? 



3. Do they especially extirpate certain kinds of natural 

 plants or weeds, and bring up others ? 



3. Experiments with burned clay what are the qualities which 

 fit a clay for burning. 



Burned clay has by many been recommended as a useful 

 application to the land ; and in numerous instances it has been 

 a source of profit to those who have employed it.* Mr Wood- 

 ward states that it renders the soil more friable, so that it can 

 be worked with less labour, and especially aids the culture of 

 green crops. On a crop of wheat grown upon drained Oxford 

 clay, Mr Pusey states that, in 1845, it added eight bushels to 

 the produce of grain yielded by one of his fields. 



No manure gave . . 37f bushels per acre. 



80 yards burned clay (cost 45s.), 45| 



80 do., and sheep folded, . 47^ 



* See especially General Beatson's New System of Cultivation, second edi- 

 tion; 1821. Also papers in the Royal Agricultural Journal by Mr Pym, iii. p. 

 323; Mr Randell, v. p. 113; Mr Pusey, vi. p. 477; Mr Mechi, vii. p. 297; Mr 

 Poppy, vii. p. 142 ; and Mr Long, vii. p. 245. 





