Now reverse the conducting tube, and allow the remaining gas to pass into some distilled water contained in a beaker. The gas bubbles will be completely absorbed, and when the gas ceases to be evolved, be careful to withdraw the conducting tube from the liquid, so as to prevent it being sucked back into the hot tube.

25. Tests for ammonia.

(a) Observe the pungent and very characteristic smell which the solution of ammonia in water possesses.

(b) Place a piece of reddened litmus paper above the solution, and observe that the vapour given off is able to change the colour from red to blue. Place the litmus paper in the solution, and the change will be still more marked.

4

(c) Hold a glass rod which has been dipped in fuming hydrochloric acid over the solution of ammonia it will at once form white fumes of ammonium chloride, caused by the union of the acid and volatile. alkali, as ammonia is sometimes called.

Hydrochloric acid and ammonia yield ammonium chloride :

HCI + NH3 NH4Cl.

26. The residue from the preparation of ammonia from ammonium chloride and lime is calcium chloride. Dissolve a portion of the residue contained in the flask used to prepare ammonia, in water, filter from excess of lime, and evaporate the solution to dryness. A white salt results, which is detached from the evapo

rating basin, and preserved in a well-stoppered bottle for future examination.

27. Preparation of ammonium nitrate.

Nitric acid, when neutralized with ammonia, yields ammonium nitrate and water:

HNO3 + (NH4) HO= (NH) NO3 + H2O.

35

=

80 +18.

63 + Place some nitric acid (21) in an evaporating basin, and dilute with twice its bulk of water; add ammonia solution (24) cautiously, and with constant stirring until a drop of the liquid ceases to colour litmus paper red. Observe that as the ammonia is added the red colour caused by the nitric acid disappears, and a point is reached when the liquid neither reddens litmus paper nor turns it blue. When this is the case the acid is said to be exactly neutralized, and the addition of ammonia must be stopped. Evaporate the solution of ammonium nitrate thus obtained, until all the water is expelled; when this is the case, withdraw the lamp and allow to cool; a cake of fused ammonium nitrate is then obtained. If the salt does not solidify on cooling, heat must be again applied.

28. Preparation of nitrogen monoxide (nitrous oxide).

When ammonium nitrate is heated, nitrogen monoxide and water are produced. Thus:

(NH4) NO = NgO + 2 HgO.

Break the cake of ammonium nitrate (27) into small pieces, and introduce them into a small dry flask

provided with a conducting tube as in 6. Heat gently, and after allowing the air in the flask to be expelled, begin to collect the gas which is produced. As this gas is soluble to a considerable extent in cold water, it is better to fill the pneumatic trough with warm water, in which the gas is much less soluble. Collect four jars of the gas, and then withdraw the conducting tube from the trough. Do not heat till all the ammonium nitrate is decomposed, as towards the close of the evolution of gas the decomposition sometimes becomes complex, and other gases are generated so rapidly that an explosion may occur.

29. Properties of nitrous oxide.

Combustible substances burn in nitrogen monoxide almost as brightly as in oxygen. They decompose the gas, uniting with its oxygen to form oxides, and leaving unaltered nitrogen.

Burn a taper, phosphorus, and sulphur in this gas, in the same manner as they were burned in oxygen. The products of combustion are the same, namely, carbon dioxide, phosphorus pentoxide, and sulphur dioxide; but there is in addition a residue of nitrogen.

30. Preparation of nitrogen dioxide (nitric oxide). When nitric acid acts upon metals. such as copper or mercury, nitrogen dioxide, water, and a nitrate of the metal used are produced. Thus :

Copper and nitric acid yield nitrogen dioxide, copper nitrate, and water :

Place some copper turnings in a flask provided with a funnel and conducting tube, as in the figure. Cover the copper with a layer of water, and add nitric acid by degrees until the gas comes off steadily. Fill two

=

31. Properties of nitrogen dioxide (nitric oxide). (a) Nitrogen dioxide readily unites with free oxygen, forming higher oxides of nitrogen which have a brown colour, 2 NO + 0 N2O3 and NO +0 = NO2. Remove a jar of the gas from the pneumatic trough and expose it to the air. Observe at once the formation of red fumes, consisting chiefly of nitrogen tetroxide, (NO2). Now dip the mouth of the jar under water, and observe that these fumes disappear owing to their solubility in water, and at the same time observe the rise of water in the jar.

(6) Allow a few bubbles of oxygen to pass into the bottle half filled with nitrogen dioxide, and observe as

before the formation of red furnes, and the rise of water in the jar as these dissolve.

(c) Nitrogen dioxide does not support the combustion of a taper, but phosphorus, when burning very brightly, is not extinguished when placed in the gas. Place a small piece of dry phosphorus in a spoon, light it, and place it in a jar of nitric oxide: it will be extinguished. Now heat it strongly in the gas flame, and again place it, whilst burning brightly, in the gas, and observe that it continues to burn.

32. Preparation of carbon dioxide (carbonic acid gas).

FIG. 9.

When hydrochloric acid acts on calcium carbonate, carbon dioxide, calcium chloride, and water are produced.

Thus :
CaCO3 + 2 HCI

100 + 73

Place some pieces of marble (calcium carbonate) in a flask with funnel and conducting tube, pour some water over it, and then a little hydrochloric acid;