116 A PRACTICAL TREATISE 



but, if this be g-uarded against, the only sensible effect of cal- 

 cination is to deprive it of its aqueous particles, and thus to 

 reduce its weight ; for the sulphuric acid which it contains 

 cannot be expelled by the most violent heat of the furnace. 

 The only object to be gained by burning it is, therefore, to 

 bring it into as fine a powder as possible, w^hich, when it has 

 been submitted to the fire, is comparatively easy : lying also 

 in a less compass, the carriage is besides cheaper. When 

 sold in that state by the London dealers, it however costs about 

 45, 6^. per bushel ; though, when merely ground, without 

 having" been burned, but brought to the condition of coarse 

 meal, which answers all its purpose as manure, it may be pro- 

 cured at 25. : we shall therefore confine our observations to its 

 application when raw. 



The soils to which it is the most congenial are the light, 

 dry, sandy, gravelly, and chalky : to heavy loams, strong clays, 

 and to wet land, it seems to yield no benefit, unless the former 

 happens to have been well limed. It was long thought that 

 g"ypsum, being itself calcareous, could not be applied with any 

 advantage to soils which were impregnated with similar mat- 

 ter ; and as the analysis of its properties shovv^s that it contains 

 both alkali and sulphuric acid, which are known to become 

 neutralized when combined in just proportions, it was also, 

 therefore, generally imagined that its eflects upon vegetation 

 would, in certain cases, be scarcely perceptible. These con- 

 clusions have, however, led to much misapprehension in its 

 use as a manure ; for, in the first case, experience has proved 

 it to be beneficial when laid upon limestone soils, or upon land 

 which has been saturated wnth chalk or lime ; and, in the 

 second, although alkalies and acids, when acting solely upon 

 each other, are rendered neutral, yet, when the resulting com- 

 pound is applied as a dressing to land, its effect has in many 

 instances been found eminently useful. The causes which 

 have produced these effects are, however, far too obscure, in 

 the present state of chemical knowledge as applied to the 

 nature of soils, to allow of more than mere conjecture ; and 

 would lead to a discussion which could prove interesting to 

 only a very limited number of our readers. 



Upon exhausted land, or upon soils containing little vegeta- 

 tive mould, or deprived of putrescent manure, it will prove 

 powerless ; but it succeeds well after an application of dung, 

 or of green crops ploughed down. It produces, also, more 

 effect in dry, th^n when laid on in wet weather. A watery 



