78 president's address — section b. 



to store it in sack^. owing to the water from the atmosphere forming a 

 concentrated solution of calcium nitrate which gradually leaks away. 



The production of nitric acid and nitrates from nitrogen is of 

 special interest, not only in its relation to agriculture, but because 

 of the large quantity of those substances required for the manufacture 

 of explosives and dyes and for chemical industry generally. 



The syiithesis of ammonia from nitrogen and hydrogen is now being 

 carried on in Germany, and the process may be said to have become 

 successful from the time that Haber worked out the influence of 

 temperature on the equilibrium constant of this reaction. The most 

 favorable temperature for combination is found to be about 650° C. 

 The combination of nitrogen and hydrogen is favoured by increase 

 of pressure, and in Germany at the present time about 200 atmospheres 

 pressure is used. 



Many catalytic agents have been found for this reaction. Man- 

 ganese, iron, and uranium are amongst the most suitable. These 

 catalytic agents will act satisfactorily only in absence of oxygen or 

 moisture in the mixed gases. Gases are therefore purified from oxygen 

 and moisture to begin with by the help of sodium or of chromous 

 salts. 



A yield of 10 per cent, is being obtained with this process in 

 Germany. Calcium cyanamide has been on the market longer than 

 synthetic nitrates or ammonia, as the experimental difficulties in 

 obtaining this substance are not so great as in the case of the others. 

 Calcium cyanamide readily enough yields ammonia, but it has not so 

 ffir become very popular amongst agriculturists. 



It would, indeed, have been surprising if a manure containing 

 nitrogen in quite a new form could have found favour at once. 



It has now been under trial for about seven years, and for some 

 soils and crops gives as satisfactory results as other nitrogenous 

 manures. This applies to the raising of fresh crops. 



Its use for top dressing is very limited, as it is found to injure 

 foliage. In comparing the various artificial nitrogen compounds, it may 

 be noticed that, weight for weight, calcium cyanamide contains con- 

 siderably more nitrogen than either ammonium sulphate or calcium 

 nitrate. It is probable that the whole of the nitrogen in calcium 

 cyanamide is available for plants, but the efficiency cf th's or any 

 other manure depends on soil, climate, crops, and other manures 

 given. The results of exhaustive and extended trials with all artificial 

 nitrogen manures will be awaited with interest. Those who are in- 

 terested aboiit the world's supplies of combined nitrogen have always 

 had before them the possibiUty of preventing the waste of nitrogenous 

 material in sewage. 



The sewage problem is an old one, and it is disappointing to confess 

 that even at the present time sewage is usually sent into the sea where 



