COMPOUNDS OF NITIUKJKN WITH HYDROGEN AND n.XYGEN 255 



substances which we have already had occasion to mention are the 

 amide compounds corresponding with saccharine substances. The most 

 important point to be remarked is that in the action of different 

 substances on ammonia it is the hydrogen that is substituted ; the 

 reactions proceed at the expense of the hydrogen and not of the 

 nitrogen, which remains in the resultant compound, so to say, un- 

 touched. The same is to observed in the action of various substances 

 on water. In the majority of cases the reactions of water consist in 

 the hydrogen being evolved, and in its being replaced by different 

 elements. The same takes place, as we have seen, in acids, in which 

 the hydrogen is easily displaced by metals. This chemical mobility of 

 hydrogen is distinctly connected with the great lightness of the atoms 

 of this element. 



In chemical practice 21 ammonia is often employed, not only for 

 saturating acids, but also for accomplishing reactions of double 

 decomposition with salts, and especially in separating insoluble basic 

 hydroxides from soluble salts. Let MHO stand for an insoluble basic 

 hydroxide, and HX for an acid. The salt formed by them will have a 

 composition MHO + XH - H 2 0=MX. If aqueous ammonia, NH 4 OH, 

 be added to a solution of this salt, then the ammonia will change 



n In practice, the applications of ammonia are very varied. The use of ammonia as a 

 stimulant, in the forms of the so-called ' smelling salts ' or of spirits of hartshorn, in cases 

 of faintness, &c., is known to everyone. The volatile carbonate of ammonium, or a 

 mixture of an ammonium salt with an alkali, is also employed for this purpose. Ammonia 

 also produces a well-known stimulating effect when rubbed on the skin, for which reason 

 it is sometimes employed for outward applications. Thus, for instance, the well-known 

 volatile salve is prepared from any liquid oil shaken up with a solution of ammonia. A 

 portion of the oil is thus transformed into a soapy substance. The solubility of greasy 

 substances in ammonia, which proceeds from the formation both of emulsions and soaps, 

 explains its use in extracting grease spots. It is also employed as an external application 

 for stings from insects, and for bites from poisonous snakes, and in general in medicine. 

 It is also remarkable that in cases of drunkenness a few drops of ammonia in water taken 

 internally rapidly renders a person sober. A large quantity of ammonia is used in 

 dyeing, either for the solution of certain dyes -for example, carmine or for changing 

 the tints of others, or else for neutralising the action of acids. It is also employed in 

 the manufacture of artificial pearls. For this purpose the small scales of a peculiar 

 small fish are mixed with ammonia, and the liquid so obtained is blown into small hollow 

 glass beads, shaped like pearls. 



In nature and the arts, however, the ammonium salts, not free ammonia, are most 

 frequently employed. In this form a portion of that nitrogen which is necessary for the 

 formation of albuminous substances is supplied to plants. Owing to this, a large 

 quantity of ammonium sulphate is now employed as a fertilising substance. But the same 

 part may be fulfilled by nitre, or by animal refuse, which in putrefying gives ammonia. 

 The nitre of the soil is formed from these ammonia-giving substances, because nitrogen 

 in combination with hydrogen is easily converted into oxygen compounds of nitrogen, as 

 we shall afterwards see. For this reason, if an ammoniacal (hydrogen) compound be 

 introduced into the soil in the spring, it will be converted into a nitrate (oxygen salt) 

 in the summer. 



