284 SOILS AND MANURES 



salts depends solely upon the amount of potash they 

 contain. It has been suggested that the presence of the 

 magnesium compounds may add to their efficiency, but 

 there is no experimental evidence to support this view, 

 and it is theoretically possible only in the very rare 

 cases in which the soil is deficient in magnesium salts. 



Influence of Chlorides. The presence of a large amount 

 of common salt in kainite makes it specially suitable 

 as a manure for mangolds, but for some other crops it 

 is considered highly objectionable. Chlorides certainly 

 have a deleterious effect on delicate plants, e.g., many 

 flowers and fruits, and for horticultural work it is better 

 to avoid any risk of this kind by employing sulphate of 

 potash or the calcined sulphate of potash and magnesia. 

 As operations are generally on a much smaller scale, 

 the difference in price is of less importance. On most 

 of the common agricultural crops, the effects of chlorides 

 are deleterious rather than beneficial, but the quantities 

 present in an ordinary dressing of kainite have very 

 little effect of any kind. It may be noted in this con- 

 nection, however, that for the same quantity of potash, 

 a dressing of kainite contains a much larger quantity of 

 chlorine than one of muriate of potash. The former, it 

 is true, contains a smaller proportion of chlorine, but 

 as it contains only about a fourth or a fifth of the potash, 

 much larger quantities of the manure must be employed. 



Comparison of Sulphate and Muriate. Muriate of 

 potash is sometimes compared unfavourably with sul- 

 phate of potash, but the difference between them has 

 probably been exaggerated. The former is more soluble 

 and often contains a larger proportion of potash. The 

 presence of chlorine is perhaps a disadvantage for cer- 

 tain purposes, but it is obvious that this cannot apply 

 to circumstances in which kainite can be used with 

 safety. If the sulphate can be obtained at the same 



