104 PHOSPHATE OF LIME. 



100 lbs. of gypsum has the power of fixing as 

 much ammonia as 6000 lbs. of horses urine, 

 even assuming that no loss would occur in the 

 absorption by the plants of all the nitrogen of 

 the latter manure. And if again it is admitted, 

 and anlysis proves that it is so, that 100 

 pounds of grass contain one pound of nitrogen, 

 then every pound of nitrogen that is added to 

 a soil, must produce 100 pounds of grass, and 

 this increased produce is effected by little more 

 than four pounds of gypsum. 



The decomposition of gypsum by this pro- 

 cess of absorption of ammonia, goes on very 

 slowly, and this explains why the action of 

 gypsum lasts for so many years. 



The benefits arising from the use of burnt 

 clay and the fertility of ferruginous soils may 

 all be explained on the same principle, the 

 power these matters possess oY fixing the am- 

 monia of the atmosphere, and subsequently by 

 their solution in water, yielding it to the plant ; 

 indeed all soils, to a greater or less extent, pos- 

 sess the power of absorbing gaseous matter. 

 It has been proposed to sprinkle sulphuric 

 acid over calcareous soils to produce gypsum 

 artificially, but the experiment has not, we 

 believe, ever been tried. 



It would be alike foreign to the purpose in- 

 tended in the publication of this treatise, and 

 useless, to cite examples of the beneficial effects 

 which have resulted from the use of this valua- 

 ble agent. All who wish to know every thing 

 that relates to this and other manures will do 

 well to consult Mr, Cuthbert Johnson's work 

 on Fertilizers. 



