Polytechnic Association Proceedings. 585 



which must be obtained from the soil. The sulphates named easily 

 yield to the growing plant this required sulphur. In this connec- 

 tion, it may be remarked that Peschi6r observed that gypsum laid 

 on the leaves of plants is gradually converted into carbonate of 

 lime. 



It has also been observed that sulphuric acid, in a very diluted 

 state, has precisely the same effects upon crops as that observed 

 when sulphate of lime or sulphate of soda is used. 



The effects which the foregoing sulphates exert upon plants 

 depend upon their relative solubility in water, by means of which 

 they can enter into the roots. An imperial gallon of pure water, at 

 the ordinary temperature, will dissolve, of 



Gypsum (burned), about 1-6 pounds. 



Gypsum (unburned), about 1-4 do 



Sulphate of potash, about 1 1-2 do 



Sulphate of soda, about 1 12 do 



Sulphate of soda, crystalized 3 1-2 do 



Sulphate of magnesia 4 do 



Gypsum is the cheapest, and, in moist climates, most economical, 

 since it is sufficiently soluble to afford the plant as much as it might 

 require. In dry seasons the use of sulphate of soda and magnesia 

 is recommended. 



The chemical composition of the soil determines in a greater 

 degree, however, the nature and extent of their chemical action. 

 If either potash, soda, magnesia or lime already abounds in the 

 soil, the good effects of the sulphate may depend entirely on the 

 sulphuric acid. If the land is deficient in lime, then the gypsum 

 will act in virtue of its sulphuric acid not only, but also of its 

 lime. Its effects will, therefore, be more marked than when the 

 soil is naturally calcareous, or artificially made so. The same will 

 be true of the other sulphates. 



Those sulphates, therefore, should be chosen, the base of which 

 the soil, to which they are to be applied, is most deficient; and it 

 may be that two or more combined are required. The composition 

 of the crops to which they are applied should also be taken into 

 consideration. 



The differences in the relative proportions of the ingi-edients 

 present in their ash, will be seen from the following table: 



