40 PRACTICAL FARM CHEMISTRY. 



crops on some soils. As a general thing, however^ 

 soda, chlorine, as also magnesia — which is an oxide 

 of the metal magnesium — are present in sufficient 

 quanities in the soil; and we have no reason what- 

 ever to worry about means how to get them. This 

 is also generally the case with silica (oxide of sili- 

 con, silic acid), as it constitutes a large percentage 

 of our common soils in the shape of finely divided 

 quartz, flint, rock crystal. 



Chlorine, as stated, acts favorably upon some 

 plants under certain conditions. From this it should 

 not be inferred that the substance is a safe plant 

 food. It is death to most plants if applied freely. 

 Salt is recommended for killing weeds. The execu- 

 tioner, in this case, is the chlorine in the salt, and 

 we have to handle this substance somewhat care- 

 fully. The German potash salts (muriate, kainit) 

 contain considerable chlorine, either as impure salt 

 or as chloride of potash, and large applications on 

 some soils and for some crops may result in injury 

 and disappointment. 



Sulphur enters plant structure in comparatively 

 small quantities only, and as it is most abundant in 

 nature, and cheaply obtained, hardly deserves 

 serious consideration in its character as 

 ^ ^ ^' plant food. In its combinations, how- 

 ever, it looms up as a most important agent of 

 rendering other plant foods available, and of pre- 

 venting their waste and loss. Combined with 

 oxygen, it appears as the well-known, cheap, 

 powerfully corrosive substance, "sulphuric acid,'' 

 and thus it usually appears in plant structure. 



In gypsum, or sulphate of lime, we have a combi- 

 nation of sulphuric acid with lime and water; in 

 plaster Paris the same compound without water. 



