Steam is blown through this solution of ammonia and con- 

 densed in sulphuric acid, when the compound sulphate of 

 ammonia is formed by combination between the ammonia 

 and the acid. 



In a similar manner, sulphate of ammonia is obtained 

 from coke-ovens, blast-furnaces, shale-oil works, and to a 

 slight extent in the manufacture of charcoal from bones. 

 In France, a certain amount is derived from the ammoni- 

 acal liquids from cesspools. Proposals have also been put 

 forward for producing sulphate of ammonia by the heating 

 and destructive distillation of wool refuse and other animal 

 matter containing nitrogen, and from peat ; but these 

 methods are not yet of practical importance. 



The production of sulphate of ammonia in this country 

 has steadily increased for a number of years ; the output 

 having risen from about 75,000 tons in 1883 to 151,500 tons 

 in 1893, an d 196,000 tons per annum at the present time. 

 The amount produced in the whole of Europe at present is 

 estimated by Sir William Crookes* at about 400,000 tons 

 per annum. 



Sulphate of ammonia belongs to the class of Nitrogenous 

 Manures i.e., those which are valuable for the nitrogen they 

 contain. We must, therefore, consider it as a source of 

 nitrogen only ; bearing in mind that if crops require other 

 substances, they must be supplied from other sources. We 

 will, therefore, first deal with the plant's requirements as to 

 nitrogen, and the effect of nitrogenous manurings generally. 



SUBSTANCES ESSENTIAL FOR PLANT GROWTH. 

 There are in all ten substances which are absolutely essen- 

 tial for plant growth that is, if any one of them is deficient 

 or absent from the soil, the crop grown will be deficient or 

 will fail accordingly. Many other substances are usually 

 taken up by plants ; but these can be dispensed with. Of 

 the essential elements, the majority are supplied naturally 

 in ample quantity carbon chiefly by the carbon dioxide 

 (carbonic acid) in the air, hydrogen and oxygen in water, 

 lime, magnesia, iron, and sulphur as constituents of the soil ; 

 though, as we shall see, the quantity of lime may be deficient. 

 We find, therefore, that the substances that the farmer must 

 supply to his crops are usually only the three nitrogen, 

 phosphates, and potash ; and even of these, potash is some- 

 times not required, as it often occurs in large quantities in 

 the soil. 



NATURAL SUPPLIES OF NITROGEN TO THE PLANT. 



Of all the essential constituents, nitrogen is most likely 



to be lacking in any state in which it can be used by plants. 



There is, of course, an unlimited quantity of free nitrogen 



in the air ; but in that state it is useless, for plants can only 



* British Association Presidential Address, 1898. 



