120 



considerable pressure and, therefore, at a temperature higher than 

 that of steam from a kettle, the chemical action known as hydro- 

 lysis is brought about. The fats are decomposed and yield a 

 mixture of " fatty acids" and a watery solution of glycerine. 

 From the former the liquid portions are squeezed out and the re- 

 maining solid ones, melting at considerably higher temperatures 

 than the original tallow, are used for the manufacture of candles. 

 From the watery solution the glycerine is, by suitable means, 

 extracted, and serves as the starting point in the manufacture of 

 such explosives as nitro-glycerine and dynamite. The mention of 

 these words recalls that overwhelming subject of the war which we 

 cannot long exclude from our thoughts. Even in the com- 

 paratively perfect security of Bournemouth we experience, in the 

 darkened state of our streets, one of the minor consequences of 

 the war. Many gas-lamps remain unlighted. In this sentence we 

 have a text for the next division of our subject, the use of lime 

 in the coal gas industry. The crude coal gas, after coming from 

 the retorts and bubbling through water in a great pipe, called the 

 hydraulic main, contains many impurities. These give it a 

 peculiarly foul smell, and, if not removed, would yield products of 

 combustion most injurious to health. Lime is one of the sub- 

 stances used to effect purification in some, although not in all, 

 gas works. For this purpose the lime, prepared as usual by 

 heating limestone or chalk, is carefully slaked and, when quite 

 cold, placed in a special apparatus known as a " lime purifier." 

 The crude gas is passed through the purifier so as to bring it into 

 intimate contact with the lime, which retains the sulphuretted 

 hydrogen and other objectionable impurities. In the hydraulic 

 main, already referred to, two layers of liquid are found. The 

 lower is crude coal-tar, the upper and watery one contains various 

 compounds of ammonia, and is known as ammonia liquor. To 

 obtain free ammonia from this the liquor is heated with lime. The 

 lime retains the various acids with which the ammonia was 

 associated, and the ammonia itself passes on to another part of the 

 apparatus where it is absorbed by sulphuric acid. It is in this way 

 that the sulphate of ammonia is made which some of you probably 

 use for your lawns and other purposes in the garden. The value 

 of sulphate of ammonia in horticulture and agriculture is mainly 

 due to the combined nitrogen which it contains. In recent years 

 several methods have been, applied to solve the problem as to how 

 the illimitable store of free nitrogen existing in the air may be 

 drawn upon so as to render it available for agricultural and other 

 purposes. To give even a brief account of these would require a 

 separate lecture ; I shall now simply mention them in so far as is 

 necessary to show how use is made of lime in this department of 

 chemical industry. By passing air through an enormous electric 

 arc a small fraction of the nitrogen and oxygen are induced to 

 combine and ultimately to yield nitric acid. Much of the acid thus 

 made is neutralised with lime and so converted into calcium 

 nitrate. This product is known by various names such as air 



