Scientific Agriculture. 



[August, 1908. 



able supply of nitrates is restricted, the 

 question of the continued fertilization 

 of the soil is an exceedingly urgent one. 

 With regard to the supply of animal 

 manure (the use of which as a supply of 

 plant nitrogen has obtained in all ages, 

 although it is only during the last cen- 

 tury that the reason of its beneficial 

 action was understood), the production 

 is diminishing rather than increasing. 

 Moreover, with more enlightened know- 

 ledge of hygiene, even if this fertilizer 

 were to become available in sufficient 

 quantities, it is questionable whether 

 for this reasou alone its general use for 

 agricultural crops would be adopted. 



Among the nitrogenous chemical 

 manures, sulphate of ammonia is im- 

 portant. The fertilizer is produced by 

 the destructive distillation of coal and 

 shale, and is a by-product in the manu- 

 facture of gas. Although its manu- 

 facture is extending, it must always be 

 quite insufficient to meet the demand of 

 the agriculturists. 



The main supply of nitrogen for ferti" 

 lization is at present chiefly obtained 

 from natural deposists of nitrates which 

 occur in certain countries. With respect 

 to this source of plant nitrogen also, the 

 available quantity is limited, and in view 

 of the enormous extension of cultivated 

 areas demanding scientific fertilization, 

 the day is not distant when the output 

 of this fertilizer will decrease and will 

 ultimately become exhausted. Of these 

 fertilizers the two best known are the 

 nitrates of potash and soda. Both of 

 these are found in considerable natural 

 deposits, the former in India and Persia, 

 aud the latter in Chili. Nitrate of soda 

 is known as Chili Salpeter, and is used 

 very extensively in agriculture. It is 

 also largely used in the manufacture of 

 nitric acid and of other chemicals, for 

 as has been said, the extreme inertness 

 of the free gas nitrogen has caused the 

 naturally existing supply of the world's 

 nitrates to be resorted to for the forma- 

 tion of many new nitrogenous combina- 

 tions. In this way the available deposits 

 are being rapidly exhausted, and in order 

 to insure the continued prosperity of 

 many agricultural crops, it is imperative 

 that a new supply of nitrates be forth- 

 coming. Where then, when the natural 

 deposits have disappeared, will agri- 

 culturists turn for their new supply of 

 nitrogen of fertilizers ? The most ready 

 means of satisfying this demand which 

 suggests itself , is to tap the great air 

 reservoir of its nitrogen, and then to 

 discover some way of combining it chemi- 

 cally with suitable substances. 



The atmosphere may be described as an 

 aerial ocean surrounding the earth 



Prom the time of Aristotle until less than 

 one hundred and fifty years ago it was 

 regarded as one of the four elements. 

 It is now known to consist almost 

 entirely of a mechanical mixture of the 

 two gases nitrogen and oxygen, in the 

 proportion of about four volumes of the 

 former to one of the latter. A graphic 

 representation of this proportion may 

 be had by inscribing a circle within a 

 square. In such a figure a circle will 

 represent the nitrogen present in the 

 atmosphere and the four spaces at the 

 corners of the square, the oxygen. 



Besides the nitrogen contained in the 

 atmosphere in chemical mixture with 

 oxygen, there are also present traces of 

 nitrogen in chemical mixture with 

 hydrogen, and also with hydrogen and 

 oxygen together. Of these latter com- 

 pjunds ammonia (N.H3 ) and nitric acid 

 (H.N.O3 ) are the most important to plant 

 life, but they occur in infinitesimal 

 amounts, varying according to local 

 and meterological conditions. 



The presence of ammonia in the atmos- 

 phere is chiefly due to the decomposition 

 of organic matter. The precipitation of 

 rain brings with it small quantities of its 

 compound which is thus rendered avail- 

 able for plant use. The occurrence of 

 electrical disturbances in the air pro- 

 duces nitric acid, and in India, where the 

 soil has been depleted for courtless 

 generations of cultivators, the crops are 

 dependent upon the periodical monsoon 

 for their supply of nitrogen. 



The insulation of nitrogen from the 

 atmosphere is a very simple operation. 

 A well-known method is by igniting 

 phosphorus in a receptacle containing 

 atmospheric air. The combustion of the 

 phosphorus exhausts the oxygen present, 

 and when the burning ceases the result- 

 ant gas consists of nitrogen in a fairly 

 pure condition. Another method of 

 obtaining this gas is to pass a stream of 

 dry air through turnings of red-hot 

 copper. The oxygen of the air remains 

 behind and forms oxide of copper, while 

 the nitrogen passes away alone. 



During the last few years a very 

 material advance has been made in the 

 discovery of practical metnods to com- 

 bine nitrogen with other elements on a 

 commercial scale. For this purpose there 

 are already several factories in Europe 

 and the United States engaged in the 

 manufacture of nitrogen compounds for 

 agricultural purposes. As yet this 

 newest and in some AVays most remark- 

 able of the scientific industries is in it8 

 infancy, but it has already passed 

 beyond the realms of experiment and is 

 engaging more and more the attention of 

 capitalists. The chief obstacle at present 



