AMMONIUM SALTS.

of potassium chloride and sodium nitrate.

389

When it is heated

it melts and loses one third of its oxygen, giving the nitrite KNO2, (cf. § 234). This is a soluble, white, crystalline solid.

Potassium cyanide (KCN) is a white, deliquescent solid, very soluble in water. The solution is very alkaline, owing to hydrolysis. Exposed to air, the cyanide is converted into carbonate and prussic acid (cf. § 290). It is very poisonous. It is used to prepare electroplating solutions (cf. § 464), to extract gold from its ores (cf. §§ 419 and 468), and as a reagent. Potassium cyanide is made by heating a mixture of potassium ferrocyanide (cf. § 496) with potassium carbonate.

(1) K4Fe(CN)6 →→→→4 KCN+[Fe(CN)2].

(2) K2CO3+[Fe(CN)2] →→→→ 2 KCN+(FeCO3).

(3) (FeCO3) →→→→→ FeO+CO2 1.

Potassium thiocyanate (KSCN) is a soluble, white crystalline solid, used in the laboratory to detect ferric salts.

Potassium hydrogen tartrate (KHCHOь) is also called potassium bitartrate, potassium acid tartrate, and "cream of tartar" (cf. § 280). It is a white, crystalline solid, requiring 253 times its weight of water, at 10° C., to dissolve it. The corresponding sodium salt is very soluble.

427. Ammonium Salts. The formation of ammonium salts by the neutralization of acids by ammonia water is described in § 210. The radical NH4 has not been isolated, because it breaks up into ammonia and hydrogen. Most ammonium salts are white, soluble solids, which, except for their instability, resemble the corresponding potassium compounds.

Ammonium amalgam is a bulky, metallic substance resembling sodium amalgam (cf. § 411). It is formed when sodium

amalgam reacts with a concentrated solution of ammonium chloride.

Na, Hg+NH,Cl →→→→→ NH4, Hg+NaCl.

Ammonium amalgam breaks up into ammonia, hydrogen, and mercury.

Ammonium chloride is used in soldering, in making galvanized iron (cf. § 448), and for "sal ammoniac" batteries, as well as in the preparation of ammonia and as a reagent in the laboratory. Ammonium sulphate, (NH4)2SO4, is an important fertilizer. Ammonium nitrate, NH4NO3, is a white, deliquescent solid (cf. § 85). It is used in preparing nitrous oxide (cf. § 238).

Ammonium hydrogen tartrate, NH1HCHО6, is difficultly soluble, like the corresponding potassium salt.

Ammonium phosphate is (NH4)2HPO4. Like the corresponding sodium salt, it is used as a source of PO4 in the laboratory. Ammonium oxalate, (NH4)2C2O4, is a source of oxalate ions,

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Ammonium carbonate, (NH4)2CO3, is used for the carbonate ions of its solution. The commercial salt is made by heating ammonium sulphate with calcium carbonate. The ammonium carbonate sublimes (cf. § 211).

(NH4)2SO4+CaCO3 → (NH4)2CO3 ↑ +CaSO4.

The product is not pure (NH4)2CO3, but contains NHHCO3 and ammonium carbamate, NH2COONH4. When the solution of the impure salt is treated with carbon dioxide, it gives the pure salt as a precipitate. Ammonium carbonate breaks up readily into ammonia, carbon dioxide, and water. For this reason it is used in some baking powders. As "solid ammonia" it is used for smelling salts and as a water softener.

Ammonium sulphide, (NH4)2S, is made as stated in § 254. It is a common source of sulphide ions (S) in the laboratory. The substance is readily dissociated:

(NH4)2S2 NH3+H2S.

The hydrogen sulphide is oxidized by the air, and sulphur is liberated. This unites with the unchanged ammonium sulphide to give yellow ammonium sulphide, which is (NH4)2S, (NH4)2S2, etc. The same substance is formed from " colorless " ammonium sulphide and sulphur.

Ammonium salts are used so generally in the laboratory because they are soluble, and, further, because they can be removed at any time from a mixture, owing to the ease with which they are dissociated into volatile materials. The test for ammonium salts is that they all react with lime, giving ammonia. 428. Exercises.

1. If the molecule of sodium is monatomic (cf. § 411), how does the weight of a liter of its vapor compare with that of a liter of oxygen under the same conditions? Answer the same question for potassium.

2. What products would be formed at each electrode in the electrolysis of ammonium chloride? Of ammonium nitrate?

3. How would you prepare sodium chlorate, ammonium hydrogen carbonate, sodium potassium tartrate, potassium silicate, potassium oxalate, ammonium mono-hydrogen phosphate?

4. Write the equations showing the preparation of potassium carbonate by the Le Blanc process.

5. All four substances in the equation of § 419 are soluble. Under what conditions can the reaction take place?

6. Which of the following gases would you dry with solid caustic potash: ammonia, chlorine, hydrogen sulphide, carbon monoxide, carbon dioxide, oxygen, hydrogen? What reactions would take place with the others?

7. How would you distinguish an ammonium salt from one of potassium or sodium? How distinguish between a potassium salt and a sodium salt?

CHAPTER XXXI.

THE ALKALINE-EARTH METALS.

429. The Group. The " alkaline-earth" metals (also called the "calcium family ") form a part of the second periodic group, and are intermediate between the alkali metals and the "earth" metals, such as

aluminum. The group consists of calcium, strontium, and barium. While magnesium really belongs with the metals glucinum, zinc, cadmium, and mercury, in a separate division of Group II, yet many of its properties ally it with the calcium group, and we

include it with them in this chapter. The metal radium also belongs in this group. Magnesium

reacts with water at 100° C.; the others even at the ordinary temperature. The hydroxides of these metals are strong bases, and their salts with strong acids are neutral. The table shows that the properties of the members of the group and of their compounds, vary in the order of the atomic weights.

430. Calcium. — Calcium does not occur free, but its compounds are found in large quantities. The most abundant is the carbonate, CaCO3; this occurs as limestone, marble, chalk, calc

spar, and coral. The sulphate, CaSO4, the phosphate, Ca3(PO4)2, and the fluoride, CaF2, are also important minerals.

Calcium is a crystalline solid with a white, metallic luster. It is a little harder than lead. With water it reacts as sodium does, but less vigorously. Beyond being covered with a thin film of oxide, it does not react with dry air at the ordinary temperature. At 760° C., its melting temperature, it takes fire, giving a mixture of CaO and Ca3N2.

Calcium is obtained by the electrolysis of fused calcium chloride

S

Ga Cl.

R

Ca

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FIG. 83.

(Fig. 83). The vessel holding the chloride is of carbon, and forms the anode. The calcium chloride at the bottom of the