As a result we rarely find that a cereal crop is starving for want 

 of potash, though it is true such a thing might happen on very poor 

 land, but we invariably find that a wheat or other cereal crop is 

 greatly benefited, the yield of grain and straw being both increased, 

 by the application of a suitable nitrogenous fertilizer. 



For some years the chief sources of nitrogenous fertilizers have 

 been the nitrate fields of South America and the sulphate of ammonia 

 now produced in such large quantities in several industries. It has 

 for a long time been realized that the nitrate fields of Chile are by no 

 means inexhaustible, and although the estimates as to the time they 

 will suffice to supply the world's demands are as such estimates 

 must necessarily be somewhat discrepant, still the fact remains that 

 some time or other, and that not very distant, the cost of nitrate of 

 soda will be much increased owing to the fact that only compara- 

 tively poor material will remain to be worked. 



In addition to this important and extensive use of nitrates in 

 agriculture it must also be remembered that nitrate of soda was, 

 until quite recently, the only raw material used in the production of 

 nitric acid. Nitric acid is one of the most important of the so-called 

 heavy chemicals, as it is essential for the production of practically all 

 the more common explosives as well as for the manufacture of synthetic 

 drugs and dyes. 



The atmosphere contains some 4,000 billion tons of nitrogen, 

 or to put it in a manner which is more intelligible vast figures really 

 convey but little the nitrogen in the air resting on one square metre 

 of the earth's surface would be sufficient to produce some forty to 

 fifty tons of nitrate of soda. 



It is rather more than 130 years ago that the Hon. Henry Cavendish 

 made his remarkable " Experiments on Air " in which he showed 

 for the first time that the air consisted of oxygen and nitrogen in the 

 proportion of one to four. This he did by passing electric sparks 

 through a small quantity of air confined over mercury. After the 

 sparks had been passing for some time the volume of air was seen to 

 have diminished and on applying some lime water or other alkaline 

 liquid the volume was still further reduced. By the passage of the 

 sparks through the air oxides of nitrogen are produced. These are 

 absorbed by the alkaline solution with the formation of nitrates and 

 nitrites. More pure oxygen was then added and the sparking continued ; 

 excess of oxygen was removed by a suitable reagent, generally sulphide 

 of potassium, and it was then found that only a very minute bubble 

 of gas remained. This bubble, as was shown more than a hundred 

 years later, was Argon. By this remarkable experiment, then, Caven- 

 dish had demonstrated the true composition of the atmosphere and, 

 although he did not recognize the fact, had discovered argon and 



