CHAMBERS'S INFORMATION FOR THE PEOPLE. 



an ammonia salt say sal-ammoniac (chloride 

 of ammonium) is mixed with caustic potash 

 (hydrate of potash), a change takes place, which 

 is represented by the following equation : 



NH 4 C1 + KHO = KC1 + NH 8 + H S O. 



The K takes the place of the NH 4 , but the NH 4 not 

 being able to take the place of the K, breaks up, 

 and instead of NH 4 HO, which might have been 

 expected, we have NH 3 + H 2 O. In preparing 

 ammonia, slaked lime (hydrate of lime) is usually 

 employed instead of caustic potash. The action 

 is quite similar to that given above : 



2NH 4 C1 + CaO,H a O = CaCl, + zNH 3 + 2H S O. 



This operation is conducted in a retort ; and the 

 ammonia, if required as a gas, may be dried by 

 passing it through a tube containing fragments of 

 solid caustic potash, which retains the water ; or if 

 a solution of the gas (spirits of hartshorn) is wished, 

 it is led into vessels containing water, which dis- 

 solves it. 



If we attempt to isolate ammonium, it also 

 breaks up, and ammonia and hydrogen are pro- 

 duced. Thus, if sodium amalgam, a compound of 

 sodium and mercury, is covered with a strong 

 solution of sal-ammoniac, the sodium and the 

 ammonium change places, and we obtain chloride 

 of sodium and ammonium amalgam. This, how- 

 ever, rapidly decomposes ; hydrogen and ammonia 

 are given off, and mercury remains behind. 



The most important source of ammonia and 

 ammoniacal salts is the decomposition of animal 

 and vegetable matters containing nitrogen. Dead 

 animals and vegetables, and animal excreta, yield 

 ammonia in decomposing. When coal (the re- 

 mains of dead plants) is distilled in the manufac- 

 ture of gas, a considerable quantity of ammonia is 

 produced, and it is from this source that the 

 ammonia of commerce is chiefly obtained. 



The following salts of ammonia deserve notice 

 here. Sulphate, (NH^SO^ largely used as a 

 manure ; sal-ammoniac, N H 4 C1 ; the nitrate, 

 NH 4 NO ? , is specially interesting, on account of 

 the way in which it decomposes when heated, all 

 of the hydrogen uniting with two-thirds of the 

 oxygen to form water, while the nitrogen and the 

 rest of the oxygen form nitrous oxide gas, thus : 

 NH 4 NO 3 = 2H 2 O + N 2 O. The nitrite, NH 4 NO 2 , 

 undergoes a similar decomposition, yielding water 

 and nitrogen gas, NH 4 NO 2 = 2H 2 O + Nj, 



It has been stated above that decaying animal 

 and vegetable matters, when these contain, as 

 they generally do, nitrogen, give off ammonia ; 

 now, if ammonia, or such ammonia-producing 

 matters are exposed to air in the presence of 

 bases, especially if so exposed in a porous mate- 

 rial, such as the soil, the ammonia undergoes oxi- 

 dation, and in the first place a nitrite is produced, 

 and this nitrite is converted into a nitrate, if 

 the exposure to oxygen is long continued. What 

 nitrite or nitrate is formed depends of course upon 

 the base with which the ammonia was mixed. 

 This is the origin of nitrates in the soil, and thus 

 nitrate of potash is produced in Bengal, where the 

 soil contains potash ; nitrate of lime and nitrate of 

 magnesia in this country, where the soil contains 

 these bases. The nitrate of soda, found in exten- 

 sive layers in Bolivia, appears to have had a dif- 

 ferent origin. Nitrates and nitrites are not 

 unfrequently found in the water of shallow wells in 



322 



towns and villages ; in such cases, this usually 

 indicates that decaying animal matters, drippings 

 from dunghills, sewage, &c. have percolated 

 through the soil, and found their way, more or less 

 oxidised, into the well 



CARBON occurs free in nature in two perfectly 

 distinct forms : I. As diamond, a colourless trans- 

 parent solid, of specific gravity 3-5. It is the 

 hardest substance known ; it is found crystallised 

 in forms derived from the cube. When strongly 

 heated in air or oxygen, diamond burns, forming 

 carbonic acid. 2. As graphite, plumbago, or black- 

 lead, a black, opaque solid, with a metallic lustre, 

 crystallised in hexagonal plates. Graphite is 

 seldom found quite pure, generally mixed with 

 from one to five per cent, of iron, silica, and 

 alumina. When strongly heated in air or oxygen, 

 it burns, forming carbonic acid. In combination, 

 carbon is very widely diffused ; carbonic acid (CO 2 ) 

 occurs in atmospheric air in the proportion of 

 about four parts in 10,000. It is poured out in 

 great quantity by volcanos, and from cracks in 

 the earth's surface ; many mineral waters contain 

 carbonic acid in solution ; it is produced by the 

 combustion and by the slow oxidation (decay) of 

 animal and vegetable substances, all which con- 

 tain carbon ; and forms a large part of the air 

 expired by animals (p. 320). It is also produced in 

 the alcoholic fermentation (see p. 332). Carbon- 

 ates occur in great quantity in nature ; carbonate 

 of lime (marble, limestone, chalk, calcspar), car- 

 bonate of lime and magnesia (dolomite, mag- 

 nesian limestone) being most abundant minerals, 

 and forming the mass of many great mountain 

 chains. Carbonate of iron (p. 329) is one of the 

 most important iron ores. Carbon occurs in 

 nature combined with hydrogen in marsh gas 

 (CH 4 ), and is an essential constituent of all animal 

 and vegetable tissues. From such tissues carbon 

 may be obtained as charcoal by the action of heat. 

 When animal or vegetable substances are heated 

 to redness in such a manner as to exclude air or 

 oxygen from them, the hydrogen and oxygen (and 

 nitrogen and sulphur, if these elements are present) 

 go off with part of the carbon as gases or volatile 

 bodies, while the rest of the carbon remains be- 

 hind as charcoal. This heating or charring may 

 be conducted in either of two ways : I. The wood, 

 coal, or other substance to be charred, may be set 

 fire to in heaps so arranged that the access of air 

 is limited, only so much being admitted as is 

 necessary to burn a part of the combustible, and 

 so furnish heat enough to char the rest. This pro- 

 cess is adopted in charcoal-burning in countries 

 where wood is abundant, and in coking-ovens for 

 preparing coke for fuel. 2. By heating the sub- 

 stance to be charred in cylindrical retorts heated 

 by special furnaces outside the retorts ; in this 

 process, the gases and volatile matters, instead of 

 being burnt, are led off by pipes from the retorts 

 (see No. 31). Charcoal varies greatly in char- 

 acter according to the substances from which it 

 is prepared; thus, we have wood-charcoal, peat- 

 charcoal, coke (coal-charcoal), bone-charcoal, 

 blood-charcoal, &c. These differ from one another 

 in texture, being more or less dense, more or less 

 porous, &c. ; they also contain mixed with them all 

 the mineral matter which may have been present 

 in the substance charred. Nearly every kind of 

 charcoal has a remarkable power of absorbing 

 gases and vapours, and is therefore used for 



