Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

122 NITRITES AND NITRATES.

by removing oxygen, one of the products of the dissociation, causes the

decomposition to continue until it has become of appreciable magnitude.

This is a good example of a non-electrolytic dissociation which though actually

insignificant can be made apparent by the use of a reagent.

Sodium nitrite is the most important technically of all the salts of nitrous

acid. It is used principally for diazot!zing in the manufacture of azo-dyes.

Heat 85 g. of sodium nitrate in an iron dish, of 15 cm. diameter,

until it melts, and add 207 g. of lead a little at a time while stirring

with an iron spatula. Continue the heating until all the lead is

oxidized, which may take half an hour, and then while cooling

keep stirring in order to obtain the mass in small loose lumps.

Extract the product first with 300 c.c. of hot water and then twice

more with 100 c.c. To precipitate the lead which has gone into

the solution as plumbite, pass in carbon dioxide for a few minutes.

Filter and neutralize the filtrate cautiously with a very little dilute

nitric acid. Evaporate to a small volume to obtain crystals, collect

these on a suction-filter, wash with alcohol, and evaporate the

mother-liquor to obtain more crystals. Yield, 40-50 g.

The lead oxide can be again converted into lead by reduction

with charcoal (No. 1).

80. Potassium Nitrate from Sodium Nitrate.
    If a mixture of sodium nitrate and potassium chloride is boiled with a
    quantity of water insufficient for complete solution, the undissolved residue
    will be sodium chloride, which is the least soluble in hot water of the four
    possible salts:
    NaNO 3 + KC1 ?± KN0 3 + NaCl.

If the filtrate is cooled, potassium nitrate will crystallize, since this is the
least soluble at the room temperature.

GKAMS OF SALT SOLUBLE IN 100 GRAMS OF WATER.

Potassium nitrate

Sodium chloride

Potassium chloride

Sodium nitrate

At 10°.

21

36

31

81

At ioo°.

246

40

56

180

Thus the interaction of the salts used depends entirely upon the solu-
bility relations.
This method has had an important application in the manufacture of
potassium nitrate for the gunpowder industry.