170 CHEMICAL FERTILIZERS 



Sulphates v. Chlorides. Excepting for the single case 

 of the mangold crop, there are few occasions when chlorides 

 are needed in any quantity as a manure. Further, as 

 common salt is generally fed to cattle and horses, and all 

 the sodium chloride fed to these animals passes into the 

 manure heap, the ordinary dressings of well-kept farmyard 

 manure contain no inconsiderable amount of common salt. 

 So far as the British Isles are concerned, most districts are 

 so little distant from the sea coast that sodium chloride, 

 in the form of fine sea spray, is brought down by the rain in 

 fair amounts. On the other hand, sulphur is an important 

 element in the proteins. Sulphur, therefore, has a definite 

 use for plants, whereas chlorine has not. Some particular 

 crops, such as potatoes, are very adversely affected by any 

 quantit}^ of sodium chloride ; the harm appears to be due to 

 the chlorine, and not to the sodium. There is, therefore, as 

 a rule, a sound reason why sulphates are preferred to chlorides 

 for manurial purposes. lyooking back over the course of the 

 use of potash salts for many years, most people have been 

 struck by the fact that both the potash manure salts and 

 kainite are becoming richer in chlorine and poorer in sulphate, 

 and that there is a tendency for potassium chloride to be 

 plentiful and potassium sulphate to be very scarce. As much 

 potassium sulphate is made from potassium chloride by treat- 

 ment with sulphuric acid, there is no reason why some of the 

 cruder potash salts might not be treated in the same way. 

 Whilst sodium and magnesium chlorides are frequently 

 prejudicial to plants, the corresponding sulphates have an 

 entirely different action. This point has been experimented 

 on at Rothamsted on wheat for about 70 years. As a result 

 it has been found that sulphate of potash, although very 

 beneficial indeed, is not so much ahead of sodium sulphate 

 or magnesium sulphate as to justify any very much greater 

 price for potassium than for sodium and magnesium. Whilst 

 the addition of sulphate of potash has added 8 bushels of 

 dressed grain, the addition of sulphate of soda has added over 

 6 bushels, and the addition of sulphate of magnesia just under 

 6 bushels, but when all those substances are added, there 



