An Introduction to Chemical Science Part 18

5. They are deficient in malleability and ductility.

6. They often form liquid solutions, similar to alloys in metals.

7. Non-metals are electronegative, and with H, or with H and O, form acids.

Examine bra.s.s, bronze, bell-metal, pewter, German silver, solder, type-metal.

223. Alloys.-An alloy is not usually a definite chemical compound, but rather a mixture of two or more metals which are melted together. One metal may be said to dissolve in the other, as sugar dissolves in water. The alloy has, however, different properties from those of its elements. For example, plumber's solder melts at a lower temperature than either Ph or Sn, of which it is composed. Some metals can alloy in any proportions.

Solder may have two parts of Sn to one of Pb, two of Pb to one of Sn, or equal parts of each, or the two elements may alloy in other proportions. Not all metals can be thus fused together indefinitely; e.g., Zn and Pb. Nickel and silver coins are alloyed with Cu, gold coins with Cu and Ag.

Gun-metal, bell-metal, and speculum-metal are each alloys of Cu and Sn. Speculum-metal, used for reflectors in telescopes, has relatively more Sn than either of the others; gun-metal has the least. An alloy of Sb and Pb is employed for type-metal as it expands at the instant of solidification. Pewter is composed of Sn and Pb; bra.s.s, of Cu and Zn; German silver, of bra.s.s and Ni; bronze, of Cu, Sn, and Zn; aluminium bronze, of Cu and Al.

224. Low Fusibility is a feature of many alloys. Wood's metal, composed of Pb eight parts, Bi fifteen, Sn four, Cd three, melts at just above 60 degrees, or far below the boiling-point of water. By varying the proportions, different fusing-points are obtained. This principle is applied in automatic fire alarms, and in safety plugs for boilers and fire extinguishers. Water pipes extend along the ceiling of a building and are fitted with plugs of some fusible alloy, at short distances apart. When, in case of fire, the heat becomes sufficiently intense, these plugs melt and the water flows out.

225. Amalgams.--An amalgam is an alloy of Hg and another metal.

Mirrors are "silvered" with an amalgam of Sn. Tin-foil is spread on a smooth surface and covered with Hg, and the gla.s.s is pressed thereon.

Various amalgams are employed for filling teeth, a common one being composed of Hg, Ag, and Sn. Au or Ag, with Hg, forms an amalgam used for plating. Articles of gold and silver should never be brought in contact with Hg. If a thin amalgam cover the surface of a gold ring or coin, Hg can be removed with HNO3, as Au is not attacked by it. Would this acid do in case of silver amalgam? Heat will also quickly cause Hg to evaporate from Au.

CHAPTER XLIV.

SODIUM AND ITS COMPOUNDS.

Examine NaCl, Na2SO4, Na2CO3, Na, NaOH, HNaCO3, NaNO3.

226. Order of Derivation.--Though K is more metallic, or electro- positive, than Na, the compounds of Na are more important, and will be considered first. The only two compounds of Na which occur extensively in nature are NaCl and NaNO3. Almost all others are obtained from NaCl, as shown by this table, which should be memorized and frequently recalled.

) Na NaCl ) Na2SO4) Na2CO3) NaOH NaNO3) ) ) HNaCO3

From what is Na2SO4 prepared, as shown by the table? Na2CO3? Na?

227. Occurrence and Preparation of NaCl.--NaCl occurs in sea water, of which it const.i.tutes about three per cent, in salt lakes, whose waters sometimes hold thirty per cent, or are nearly saturated, and, as rock salt, in large ma.s.ses underground. Poland has a salt area of 10,000 square miles, in some parts of which the pure transparent rock salt is a quarter of a mile thick. In Spain there is a mountain of salt five hundred feet high and three miles in circ.u.mference. France obtains much salt from sea water. At high tide it flows into shallow basins, from which the sun evaporates the water, leaving NaCl to crystallize. In Norway it is separated by freezing water, and in Poland it is mined like coal. In New York and Michigan it is obtained by evaporating the brine of salt wells, either by air and the sun's heat, or by fire. Slow evaporation gives large crystals; rapid, small ones.

228. Uses.--The main uses are for domestic purposes and for making the Na and Cl compounds. In the United States the consumption amounts to more than forty pounds per year for every person.

229. Sodium Sulphate.--What acid and what base are represented by Na2SO4? Which is the stronger acid, HCl or H2SO4? Would the latter be apt to act on NaCl? Why?

230. Manufacture.--This comprises two stages shown by the following reactions, in which the first needs moderate heat only; the last, much greater.

(1) 2 NaCl + H2SO4 = HNaSO4 + NaCl + HCl: (2) NaCl + HNaSO4 = Na2S4 + HCl.

The operation is carried on in large furnaces. The gaseous HCl is pa.s.sed into towers containing falling water in a fine spray, for which it has great affinity. The solution is drawn off at the base of the tower. Thus all commercial HCl is made as a by- product in manufacturing Na2SO4.

When crystalline, sodium sulphate has ten molecules of water of crystallization (Na2SO4, 10 H2O); it is then known as Glauber's salt. This salt readily effloresces; i.e. loses its water of crystallization, and is reduced to a powder. Compute the percentage of water.

231. Uses.--The leading use of Na2SO4 is to make Na2CO3; it is also used to some extent in medicine, and in gla.s.s manufacture.

232. Sodium Carbonate.--Note the base and the acid which this salt represents. Test a solution of the salt with red and blue litmus, and notice the alkaline reaction. Do you see any reason for this reaction in the strong base and the weak acid represented by the salt?

233. Manufacture.--Na2CO3 is not made by the union of an acid and a base, nor is H2CO3 strong enough to act on many salts. The process must be indirect. This consists in reducing Na2SO, to Na2S, by taking away the O with C, charcoal, and then changing Na2S to Na2O3 by CaCO3, limestone. The three substances, Na2SO4, C, CaCO3, are mixed together and strongly heated. The reactions should be carefully studied, as the process is one of much importance.

(1) Na2SO4 + 4 C = Na2S + 4 CO.

(2) Na2S + CaCO3 = CaS + Na2CO3.

Observe that C is the reducing agent. The gas CO escapes. The solid products Na2CO3 and CaS form black ash, the former being very soluble, the latter only sparingly soluble in water. Na2CO3 is dissolved out by water, and the water is evaporated. This gives commercial soda. CaS, the waste compound in the process, contains the S originally in the H2SO4 used. This can be partially separated and again made into acid. Describe the manufacture of NaCO3 in full, starting with NaCl. This is called the Le Blanc process, but is not the only one now employed to produce this important article.

234. Occurrence.-Sodium carbonate is found native in small quant.i.ties. It forms the chief surface deposit of the "alkali belt" in western United States, where it often forms incrustations from an inch to a foot in thickness. It was formerly obtained from sea-weeds, by leaching their ashes, as, by a like process, K2CO3 was obtained from land plants.

235. Uses.--Na2CO3 forms the basis of many alkalies, as H2SO4 does of acids. Of all chemical compounds it is one of the most important, and its manufacture const.i.tutes one of the greatest chemical industries. Its economical manufacture largely depends on the demand for HCl, which is always formed as a by-product. As but little HCl is used in this country, Na2CO3 is mostly manufactured in Europe. The chief uses are for gla.s.s and alkalies.

236. Sodium.--Na must always be kept under naphtha, or some other liquid compound containing no O, since it oxidizes at once on exposure to the air. For this reason it never occurs in a free state.

237. Preparation.-By depriving Na2CO3 of C and O, metallic sodium is formed. As usual, heated charcoal is the reducing agent. The end of the retort, which holds the mixture, dips under naphtha.

Na2CO3 + 2 C = 2 Na + 3 CO. The process is a difficult one, and Na brings five dollars per pound, though in its compounds it is a third as common as Fe. K is as abundant as Na, but more difficult of separation, and is worth three dollars per ounce. Notice the position of K and Na at the positive end of the elements.

238. Uses.--Na is used to reduce Al, Ca, Mg, Si, which are the most difficult elements to separate from their compounds. It acts in these cases as a reducing agent.

239. Sodium Hydrate. Review Experiment 62.

Experiment 118.--Put into a t.t. 10cc. H2O and 2 or 3 g. NaOH.

Note its easy solubility. Test with litmus. Will it neutralize any acids?

240. Preparation. -- Sodium hydrate, caustic soda, or soda by lime, is made by treating a solution of Na2CO3 with milk of lime.

CaCO3 is precipitated and al- lowed to settle, the solution is poured off, and NaOH is obtained by evaporating the water and running the residue into molds.

241. Use.--NaOH is a powerful caustic, but its chief use is in making hard soap.

242. Hydrogen Sodium Carbonate.--Hydrogen so- dium carbonate, bicarbonate of sodium, acid sodium carbonate, cooking-soda, etc., HNaCO3, is prepared by pa.s.sing CO2 into a solution of Na2CO3.

Na2CO3 + H2O + CO2 = 2 HNaCO3. Test a solution of it with litmus.

Account for the result. Its use in bread-making depends on the ease with which CO2 is liberated. Even a weak acid, as the lactic acid of sour milk, sets this free, and thus causes the dough to rise.

243. Sodium Nitrate.--Sodium nitrate occurs in Chili and Peru. It is the main source of HNO3.

Review Experiments 46 and 52. From NaNO3 is also made KNO3, (NaNO3 + KCl = NaCl + KNO3), one of the ingredients of gunpowder.

By reason of its deliqcescence NaNO3 is not suitable for making gunpowder, though it is sometimes used for blasting-powder. The action of the latter is slower than that made from KNO3. NaNO3 is cheaper and more abundant than KNO3; this is true of most Na compounds in comparison with those of K.

Chapter XLV.

POTa.s.sIUM AND AMMONIUM.

POTa.s.sIUM AND ITS COMPOUNDS.

Examine K, KCl, K2SO4, K2CO3, KOH, HKCO3, KCLO3, KCN.

244. Occurrence and Preparation.--Pota.s.sium occurs only in combination, chiefly as silicates, in such minerals as feldspar and mica. By their disintegration it forms a part of soils from which such portions as are soluble are taken up by plants. The ashes of land-plants are leached in pots to dissolve K2CO3; hence it is called potash. Sea-plants likewise give rise to Na2CO3.