76 SOILS. 



When a subsoil is found to contain pyrites, or when "sulfur 

 balls " have been accidentally introduced with dressings of 

 marl, the remedy is thorough and persistent aeration of the 

 material. In the case of marls nothing more need be done ; but 

 in that of ill-drained subsoils it is best to add lime in moderate 

 dressings, to accelerate the transformation into ferric hydrate 

 or iron rust, and gypsum ; whereby the copperas becomes not 

 only innocuous but adds two beneficial ingredients to the soil. 

 The same policy will render available manure or other materials 

 which have been disinfected by means of solution of copperas. 



Halite (rock-salt), or common salt, has already been men- 

 tioned as to its occurrence in connection with the Stassfurt 

 potash salts (see above, page 71); but as rock-salt it rarely 

 exerts any injurious influence upon lands. It is, however, a 

 common ingredient of seashore lands, and is also present to a 

 certain extent in the alkali lands of the arid countries. While 

 it is true that occasionally small quantities of common salt are 

 used as an ingredient in fertilization, its usefulness in that 

 direction is exceedingly subordinate ; and it is far more gener- 

 ally to be considered as an injurious ingredient of all culti- 

 vatable soils whenever present to a larger extent than a few 

 hundredths of one per cent. It is usually considered that one- 

 fourth of one per cent of common salt renders lands unfit for 

 most culture plants. Only a few, such as asparagus, the beet, 

 the saltbushes and some others, succeed when it is present in 

 this or in larger amounts. In the case of sea water it is usually 

 accompanied by a still more injurious ingredient, magnesic 

 chlorid or bittern; which is detrimental to plant growth in 

 much smaller quantities than the common salt itself. 



Recognition of Common Salt. The presence of common salt may, 

 as a rule, be detected by the taste, well-known to every one ; when this 

 taste is very intense or somewhat bitterish, it indicates the presence of 

 bittern. The presence of salt, however, is easily verified without the 

 use of chemical reagents, by slowly evaporating some of the clear water 

 leached from the soil in a clean silver spoon. If the last few drops are 

 allowed to evaporate spontaneously, it will be easy to distinguish, even 

 with the unaided eye, the square, cubical crystals, sometimes combined 

 into cross-shape, which are characteristic of common salt. It is always 

 an unwelcome addition to the land, and as its action cannot be neu- 



