20 PLANT PRODUCTS 



perchlorate. It frequently happens that there is quite 

 enough iodine to produce a smell of that element, and traces 

 of perchlorate are also common. Cases have been recorded 

 where these impurities have reached sufficient amounts to 

 produce prejudicial effects on the crops grown, but the event 

 is too rare to be of any practical importance. The effects 

 of rare elements like iodine can be studied in the Royal 

 Agricultural Society's Reports. 



Nitrate of Lime. — In 1898 Sir William Crookes read 

 his Presidential address to the British Association at Bristol, 

 calling attention to the possible diminution in the world's 

 supply of wheat, and urged the necessity of the manufacture 

 of nitrates directly from the air. It is taking a long time 

 to reach the condition of affairs he described, though the 

 world's shortage of wheat is certainly already appearing. The 

 supply of nitrate of soda has not shown the decrease antici- 

 pated ; on the other hand, sulphate of ammonia has proved 

 to be more plentiftd, but, nevertheless, some nitrate made 

 from the air is now a practical fertilizer and after the war 

 is over may come into more general use. The chief difficulty 

 in using nitrate of lime is due to its deliquescent properties ; 

 nitrate of soda is bad enough in this respect, but nitrate 

 of lime is worse. Nitrate of lime has to be kept in casks, 

 which are by no means convenient to carry to the field. 

 When nitrate of lime is broadcast by hand it is extremely 

 unpleasant to the workers, since small dust particles 

 settle upon the workers' faces, and by dissolving in traces 

 of sweat, produce a stinging strong solution. Nitrate of 

 lime can be used in much the same way as nitrate of soda. 

 It is very quick acting, should only be used as a top dressing, 

 is instantly available, and is easily washed out of the soil. 

 When nitrate of lime is mixed with a small proportion of 

 sulphate of ammonia, a very fine dry breadcrtunb-like 

 powder is obtained, which is very convenient to handle. 

 Nitrate of lime cannot be mixed with super-phosphate 

 (see p. 35), and admixture with basic slag would be of little 

 value. One of its great advantages lies in the fact that it 

 has no useless ingredients ; the whole of the lime and the 



