ITS COMBINATION WITH ACIDS. 61 



fuses to take up any more,] it is lighter than pure water, [its specific 

 gravity is 0*875, water being 1,] has the pungent penetrating odour of the 

 gas, and its hot, burning, alkaline taste — is capable of blistering the 

 skin, and decomposing or destroying the texture of animal and vegeta- 

 ble substances. 



You will remark here the effect which combination has in investing 

 substances with new characters. The two gases hydrogen and nitrogen, 

 themselves without taste or smell, and absorbed by water in minute 

 quantity only, form by their union a compound body remarkable both 

 for taste and smell, and for the rapidity with which water absorbs it. 



Ammonia possesses also alkaline properties,* it restores the blue 

 colour of vegetable substances that have been reddened by an acid, and 

 it combines with acid substances to form salts. 



Among gaseous substances, therefore, there are some which, like car- 

 bonic acid, have a sour taste and redden vegetable blues ; others which, 

 like ammonia, have an alkaline taste and restore the blue colour ; an., 

 a third class which, like oxygen, hydrogen, and nitrogen, are destitute of 

 taste and do not affect vegetable colours. These last are called neu- 

 tral or indifferent substances. 



Ammonia, as above slated, combines with acids and forms salts, 

 which at the ordinary temperature of the atmosphere are all solid sub- 

 stances. Hence if carbonic acid gas be mixed with ammoniacal gas, 

 a white cloud is formed consisting of minute particles of solid carbonate 

 of ammonia — the smelling salts of the shops. Hence also a feather 

 dipped into Vinegar or dilute muriatic acid (spirit of salt), and then in- 

 troduced into ammoniacal gas, forms a similar white cloud, and be- 

 comes covered with a white down of solid acetate or of muriate of ammonia 

 (sal ammoniac). The same appearance is readily seen by holding the 

 feather to the mouth of a bottle containing hartshorn (liquid ammonia), 

 from which ammoniacal gas continually escapes, and by its lightness rises 

 into the air, and thus comes in contact with the acid upon the feathers. 



The fact of the production of a solid body by the union of two gases 

 (ammonia and carbonic or muriatic acid gases) is one of a very inter- 

 esting nature to the young chemist, and presents a further illustration 

 of the changes resulting from chemical combination as explained in 

 the previous lecture. 



Ammonia is little more than half the weight of common air, [more 

 nearly three-fifths, its specific gravity being 0-59, that of air being 1,] 

 hence when liberated on the earth's surface it readily rises into and 

 mingles with the atmosphere. It consists of hydrogen and nitrogen 

 united together in the proportion of three equiv^ents of hydrogen (3H 

 or H3) anil one of nitrogen (N), [see Lecture II,] and hence, it is re- 

 presented by the symbol (N + 3H), or more shortly by NH3. 100 

 parts by weight contain 82i of nitrogen and 17i of hydrogen, [correct- 

 ly 82-545 and 17-455 respectively.] 



In nature, ammonia exists in considerable quantity It is widely, 



• In the previous lectivre, the term acid was explained as applying to substances possess- 

 ed of a sour taste, and capable of reddening vegetable blues or combining with boats (pot- 

 ash, soda, magnesia, «S:v3.) to form salts ; alkalies are such as possess an alkaline taste (see 

 previous Note), restore tlie blue colour to r&idened vegetable substances, or combine with 

 acida to form salts. Of salts, nitrate of sodi saltoetrc (nitrate of potash), and glauber salts 

 (sulphate of soda), are examples. 



