214 ON THE CHEMICAL CONSTITUENTS OF SOILS. 



ferae, such as mustard, (^sinapis alba and nigra,) con- 

 tain sulphur in notable quantity. The same is the 

 case with turnips, the different varieties of rape, cab- 

 bage, celery, and red clover. These plants thrive 

 best in soils containing sulphates ; hence if these 

 salts do not form natural constituents of the soil, 

 they must be introduced as manure. Sulphate of 

 ammonia is the best salt for this purpose. It is most 

 easily procured by the addition of gypsum or sul- 

 phate of iron* (green vitriol) to putrefied urine. 



Horn, wool, and hoofs of cattle, contain sulphur 

 as a constituent, so that they will be found a valua- 

 ble manure when administered with soluble phos- 

 phates, (with urine, for example.) 



Phosphate of magnesia and ammonia forms the 

 principal inorganic constituent of the potato ; salts 

 of potash also exist in it, but in very limited quanti- 

 ty. Now the soil is rendered unfitted for its culti- 

 vation, even though the herb be returned to it after 

 the removal of the crop, unless some means are 

 adopted to replace the phosphate of magnesia re- 

 moved in the bulbous roots. This is best effected 

 by mixtures of night-soil with bran, magnesian lime- 

 stone, or the ashes of certain kinds of coal. I ap- 

 plied to a field of potatoes manure, consisting of 

 night-soil and sulphate of magnesia (Epsom salts), 

 and obtained a remarkably large crop. The manure 

 was prepared by adding a quantity of sulphate of 

 magnesia to a mixture of urine and faeces, and mix- 

 ing the whole with the ashes of coal or vegetable 

 mould, till it acquired the consistence of a thick 

 paste, which was thus dried by exposure to the sun. 



It has been formerly mentioned, that the seconda- 

 ry and tertiary limestones contain potash : marl, and 

 the calcareous minerals used for the preparation of 

 hydraulic mortar, may be particularly specified. 



* If sulphate of iron be employed, it ought not to be added in great 

 excess, and the urine must be exposed to the air for some time after, 

 for the purpose of converting the iron into the peroxide. A salt of the 

 protoxide of iron is injurious to vegetation. — Ed. 



