1 20 COAL TAR AND PART i. 



ammonia to form a salt. For example, when muriatic 

 acid is put into the liquid, it drives off the volatile gases 

 and combines with the ammonia in solution to form 

 muriate of ammonia, which is dissolved in water and 

 evaporated till it crystallises ; then it is vaporized and 

 sublimed to free it from impurities. 



When ammonia and muriatic acid are separately 

 vaporized, the two colourless transparent vapours, when 

 mixed, combine into solid muriate of ammonia, a result 

 so unexpected that as Mr. Play fair justly observes, it 

 could only have been taught by experiment. About 4,000 

 tons of muriate of ammonia are annually made from 

 gas water in England for soldering, and for making alum. 



Sulphate of ammonia to the extent of 5,000 tons is 

 annually made by adding oil of vitriol to the liquid. It 

 is also used for making alum, as well as for manure ; it 

 supplies our grain with nitrogen, an important article of 

 vegetable food. To these may be added 2,000 tons of 

 carbonate of ammonia, so that a substance that was 

 considered to be good for nothing yields 11,000 tons of 

 valuable materials, but even this quantity forms only 

 part of the enormous amount annually consumed in the 

 manufactures of Great Britain. 



Coal tar is of complicated nature, containing a variety 

 of substances, many of which are more or less volatile. 

 When it is distilled by sending a current of steam 

 through it, the steam collects the volatile parts, con- 

 denses them into naphtha; the first product is con- 

 densed steam or water with naphtha swimming on its 

 surface, the next product is dead oil, and the remainder 

 is pitch. 



By the aid of the crude naphtha thus produced, Indian 

 rubber is dissolved and waterproof clothes are made. 

 When purified by sulphuric acid, it forms a substance 

 like tar which is thrown away, and the remaining pro- 

 ducts when clarified are acid oils and neutral hydro- 



