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.