124 WHY IT PRODUCES UNLIKE EFFECTS 



ing sulphate of ammonia and carbonate of lime. Believing 

 ammonia to exist largely in the air, Liebig explained the bene- 

 ficial action of gypsum by its absorbing and fixing (forming 

 sulphate with) this ammonia. But the answer to this novelty 

 was easy. If this be the action of gypsum, why does it benefit 

 clover and not the adjoining crops, since ammonia is beneficial 

 to all and why is good done by it on one soil and not 011 an- 

 other, since all which are poor in nitrogenous matters are thank- 

 ful for ammonia ? 



2. Why does gypsum not produce equal effects on every soil? 

 The general action, as well as the special local effects of gypsum, 

 are to be explained by reference only to a considerable variety of 

 circumstances. Thus, 



a If a soil naturally abound in gypsum, or if the springs or 

 streams which water it do so, it is plain that, according to what- 

 ever theory we explain the actual effects of gypsum upon plants, 

 the addition of gypsum to such a soil can produce no sensible 

 effect. And as the soils and springs which are associated with 

 certain geological formations the new red sandstones, and 

 sometimes the mountain limestones, (Nova Scotia,) and old red 

 sandstones, (Russia,) for example are especially liable to abound 

 in gypsum, it is probable that, from geological. maps, we may, in 

 many cases, obtain important hints as to where the use of gypsum 

 is likely to fail in benefiting the farmer. 



b If a soil be so poor in lime that it is unable readily to supply 

 as much as a given crop requires, then the addition of gypsum 

 may do benefit by affording the means of readily supplying this 

 want of the plant. The same remark applies to the other ingre- 

 dient of gypsum, its sulphuric acid ; and there is little reason to 

 doubt that the good effects of gypsum are, in many cases, to be 

 ascribed to its readily yielding both lime and sulphuric acid to 

 the growing plant. 



c If the manure usually applied has contained a sufficiency of 

 sulphur in any form if gas lime, for example, has been used, 

 or woollen rags to any extent, or peat ashes, or pyritous marls 

 in all such cases as these, the apparent effects of gypsum are 

 likely to be lessened. There are, therefore, many circumstances 

 to be inquired into and investigated before we can satisfactorily 



