290 



THE POPULAE EDUCATOR 



account : hence two volumes of N 2 O 2 = two volumes of nitrogen ; 

 but this is found not to be the case, for upon removing the 

 finger, the mercury rises in the bent tube exactly one-half the 

 volume occupied by the gas. Therefore the formula for nitric 

 oxide must be NO, and not N 2 O 2 : 



NO = N + O. 

 2 = 1 + ; 



that is, the volume of nitrogen is one-half that of the nitric 

 oxide, which agrees with the result of the experiment. 



This gas has not yet been liquefied. 



Nitric trioxide, or nitrous acid (N 2 O 3 ; combining weight, 76 ; 

 density, 38). This gas is noted for its deep-red colour. The 

 most ready method of preparing it is by heating in a capacious 

 retort 1 part of starch with 8 of nitric acid. The gas liberated 

 is almost pure N 2 O 3 . 



It forms compounds called nitrites. A very minute trace of 

 any nitrite may be detected by mixing a dilute solution of potas- 

 sium iodide with starch and a little dilute hydrochloric acid. 

 Render the liquid to be tested also acid with hydrochloric acid ; 

 then mix the two liquids ; if any nitrite be present, the liquid 

 no.ll become blue. These salts may frequently be detected in 

 the well-water of towns. 



When this gas is reduced to a temperature of 18 Cent., the 

 red fumes become a dark-blue liquid. When added to water, it 

 is at once decomposed into nitric oxide and nitric acid, thus : 

 3N,O, + H a O = 2HNO, + 4NO. 



Nitric tetroxide, or nitric peroxide (NO S ; combining weight, 

 46 ; density, 23). The reddish-brown fumes which appear when 

 nitric oxide meets with oxygen are chiefly of this substance. 



It is best prepared by heating lead nitrate in a small glass 

 retort. The fumes which are given off are a mixture of peroxide 

 of nitrogen and free oxygen ; if they are conducted through a bent 

 tube which is surrounded by ice and salt, the peroxide becomes 

 jondensed into a liquid. The reaction is thus expressed: 



2(Pb2NO s ) = 2 PbO + 4NO, + O a . 



The red fumes are very suffocating, but will support the com- 

 bustion of a taper immersed in them. This compound may be 

 distinguished from the former, nitrous acid, by its power of 

 imparting to a neutral solution of potassium sulpho-cyanide, a 

 red tint; an excess of the peroxide, however, renders the liquid 

 again colourless. 



The compounds of nitrogen and hydrogen are : 



Amidogen NH, 



Ammonia NH 5 



Ammonium ...... NH. 



Amidogen (NH 2 ) is not known in a separate state, but it is 

 '.iclicved to exist as a constituent of numerous compounds which 

 chiefly belong to organic chemistry, and are termed amides. 



Anwwnia (NH 3 ; combining weight, 17 ; density, 8'5). This 

 compound receives its name from the fact that it was first pre- 

 iiared from the dung of the camels which the Arabs collected 

 i,t the temple of Jupiter Ammon, the halting-place before the 

 journey of the desert of Libya was undertaken. Nitrogen and 

 hydrogen do not combine directly with each other, but it seems 

 whenever they are liberated together by the decomposition of 

 any compound containing them, they unite to form ammonia, 

 and it appears frequently to be formed when hydrogen, in its 

 nascent state that is, just liberated from its combination 

 meets with nitrogen of the air. Thus, if iron filings be moistened 

 and exposed to the air they become oxidised, partly at the expense 

 of the oxygen of the water ; and the hydrogen as it is liberated 

 forms, with the nitrogen, ammonia, which is found in the com- 

 pound. This is also exhibited when tin, zinc, iron, and some 

 other metals are acted on by dilute nitric acid, thus : 

 9HNO, + 4Zn = 4(Zn2NO s ) + 3H S 6 + NH 3 . 



The whole action is not expressed by this formula for the 

 water which dilutes the acid is decomposed and the equation 

 may be rectified by using the liberated constituents of the water. 

 Any organic bodies which contain nitrogen when distilled in a 

 closed vessel give off ammonia. Formerly this method was re- 

 sorted to for its production from horn clippings, hence its name 

 spirits of hartshorn. It is now obtained from the refuse pro- 

 ducts of the distillation of coal in the manufacture of gas. For 

 the laboratory it may be prepared by gently heating equal 

 weights of quick-lime (oxide of calcium), made into a paste 

 with water and sal-ammoniac, which is ammonium chloride. 

 r.aO + 2NH.C1 =CaCl, + 3H 4 + 2NH S . 



The gas must either be collected over mercury or by displace- 

 ment, as in the case of hydrogen (Fig. 23), as it is one-half as 

 heavy as air. Its specific gravity is - 59, and it possesses the 

 well-known pungent odour of " smelling salts." 



When breathed it has a violent irritating power on the pul- 

 monary passages. It is a powerful base, neutralises the 

 strongest acids, and returns the colour to litmus paper reddened 

 by an acid. 



It is very soluble in water. The liquid at Cent, and 760 

 mm. pressure is capable of absorbing 1149 times its volume. If a 

 jar of the gas be held with its mouth downwards to the surface 

 of water, the water will rush into the jar as into a vacuum, and 

 unless the glass be strong the jar will probably break. 



When water containing ammonia is heated, the gas is given 

 off, so that at 20 Cent, only half the quantity of gas is re- 

 tained which the water possessed at Cent. 



When submitted to a pressure of 7 atmospheres at the ordinary 

 temperature of the air, the gas becomes a liquid, which boils at 

 38'5 Cent., and freezes into a transparent solid at 175 

 Cent. 



This fact has been advantageously applied by M. Carre to 

 freeze water. A saturated solution of ammonia is placed in a 

 strong iron vessel, which is connected by a pipe with a 

 "receiver," which is a cavity in the thick wall of a cylindrical 

 vessel. When heat is applied to the liquor ammonia, the gas 

 is given off in large quantities ; but not being able to escape, it 

 finds itself under great pressure, and begins to condense into a 

 liquid in the receiver. The interior of the cylindrical vessel is 

 filled with water, the heat is now removed from the other vessel, 

 and the temperature of the water it contains is reduced by 

 pouring cold water over it. But this renders the water it contains 

 capable of absorbing the gas again, and therefore the liquefied 

 gas in the "receiver" begins to evaporate rapidly; this, however, 

 it cannot do, without absorbing a large quantity of latent heat, 

 and hence the water which the " receiver " surrounds freezes. 



Ammonium (NHJ. Place a globule of mercury in a cavity in 

 a piece of sal-ammoniac, and moisten it with liquor ammonia ; 

 then if the positive wire of a battery be attached to the salt, 

 and the mercury be touched with the negative, the globule will 

 swell and assume all the appearance of an amalgam. When the 

 current is suspended, the mercury returns to its ordinary state, 

 giving off ammonia and hydrogen. 



There is only one way of accounting for this, namely, that 

 sal-ammoniac is a chloride of a metal (NH 4 C1), and that in the 

 ordinary way electrolysis took place the metal combining with 

 the mercury formed an amalgam. But this compound only 

 having permanence under the influence of the current, decom- 

 poses when the current is interrupted. 



Nessler's test discovers the most minute quantity of ammonia. 

 Saturate the solution supposed to contain ammonia with potash, 

 then add potassic iodide saturated with mercuric iodide. If any 

 ammonia be present, a " brick-dust " precipitate will appear. 



The composition of ammonia is discovered by leading the gas 

 through a red-hot porcelain tube, or by passing a series of electric 

 sparks. Either of these methods resolves the compound into its 

 components, which are found to occupy double the volume of the 

 gas, as might be expected from this equation, which has been 

 previously alluded to : 



NH, ==N-t-3H 

 2 =1+3; 



that is, two volumes of NH 3 become, when decomposed, four 

 volumes of the mixed gases. 



LESSONS IN GREEK. X. 



THE THIRD DECLENSION (continued). 



THERE is yet another class in the subdivision of nouns whose 

 nominatives append s to the stem (see page 258), of which the 

 stem ends in v or VT. As examples, take T\ pis, piv-os, the nose ; 

 6 $\(j>is, Se\<piv-o$, a dolphin; 6 yiyas, yiyavr-os, a giant; 6 

 oSovs, ooovr-os, a tooth (Latin, dens, English, dentist). 



Singular. 



Nom. pis. 8f\<pis. yiyas. ofiovs, 



Gen. piv-os. 5e\<plv-o$. yiyavr-os. oSovr-os. 



Dat. plv-i. 5e\<plv-i. yiyavr-i. oSovr-i. 



Ace. f>lv-a. 8e\<j>ii>-a. yiyavr-a. oSovr-a. 



Voc. plv. 5e\<pis (iv). yiyav- oSous. 



