Chapter 83

POTASSIUM AND AMMONIUM.

POTASSIUM AND ITS COMPOUNDS.

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

244. Occurrence and Preparation.--Potassium 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. Wood ashes originally formed the main source of K2CO3. From plants this substance is taken into the animal system, and makes a portion of its tissue. Sheep excrete it in sweat, which is then absorbed by their wool. Large quantities are now obtained by washing wool and evaporating the water. K2CO3 and other compounds of K are mainly derived from KCl, beds of which exist in Germany.

In the following list each K compound is prepared like the same Na compound, and the uses of each of the former are similar to those of the latter. K compounds are made in much smaller quantities than those of Na, as KCl is far less common than NaCl.

{ K KCl { K2SO4 { K2CO3 { KOH KNO3 { { HKCO3

Examine specimens of each, side by side with like Na compounds. Describe in full their preparation, giving the reactions. Also, perform theexperiments given under Na, substituting K therefor. From KOH are made KClO3 and KCN.

KOH {KCl03 {KCN

245. Potassium Chlorate.--KCl03 is made by passing Cl into a hot concentrated solution of KOH.

6 KOH + 6 Cl = KCl03 + 5 KCl + 3 H2O

Its uses are making O, and as an oxidizing agent.

246. Potassium Cyanide, KCN, is a salt from HCN--hydrocyanic or prussic acid. Each is about equally poisonous, and more so than any other known substance. A drop of pure HCN on the tongue will produce death quickly by absorption into the system. In examining these compounds take care not to handle them or to inhale the fumes. KCN is used as a solvent for metals in electro-plating, and is the source of many cyanides, i.e. compounds of CN and a metal. KCN is employed to kill insects for cabinet specimens. In a wide-mouthed bottle is placed a little KCN, which is covered with cotton, and over this a perforated paper. The bottle is inverted over the insect, and the fumes destroy life without injuring the delicate parts. HCN is made from KCN and H2SO4.

247. Gunpowder.--Gunpowder is a mixture of KNO3, C, and S. Heat or concussion causes a chemical change, and transforms the solids into gases. These gases at the moment of explosion occupy 1500 or more times the volume of the solids. Hence the great rending power of powder. If not confined, powder burns quietly but quickly. The appended reaction is a part of what takes place, but it by no means represents all the chemical changes.

2KNO3 + S + 3C =K2S + 2N + 3CO2.

From this equation compute the percentage, by weight, of each substance used to make gunpowder economically.

Thoroughly burned charcoal, distilled sulphur, and the purest nitre are powdered and mixed in a revolving drum,made into a paste with water, put under great pressure between sheets of gun metal, granulated, sifted, to separate the coarse and fine grains, and glazed by revolving in a barrel which sometimes contains a little powdered graphite.

Experiment 119.--Pulverize and mix intimately 4 g. KNO3, l/2 g. S, 1/2 g. charcoal. Pile the mixture on a brick, and apply a lighted match. The adhering product can be removed by soaking in water.

AMMONIUM COMPOUNDS.

248. Read the chapter on NH3. Also, review the experiments on bases. Examine NH4Cl, NH4NO3, (NH4)2SO4, (NH4)2CO3.

Ammonium, NH4, is too unstable to exist alone, but it forms salts similar to those of K and Na. NH3 dissolved in water forms NH4OH.

The food of plants, as well as that of animals, must contain N. It has not yet been shown that they can make use of that contained in the air, but they do absorb its compounds from the soil. All fertilizers and manures contain a soluble compound of NH4. All NH4 compounds are now obtained either from coal, in making illuminating-gas, or from bones, by distillation.

Suppose the product obtained from the gas-house to be NH4OH, how would NH4Cl be made? (NH4)2SO4? NH4NO3? Write the reactions. (NH4)2CO3 is made by heating NH4Cl with CaCO3. Give the reaction.