CHEMICALLY PURE SODIUM CHLORIDE 191

Procedure: Dissolve 25 grams of rock salt in 75 cc. of water,

hastening the action with gentle heating. To the solution add

about 1 gram of sodium carbonate dissolved in a few cubic centi-

meters of water. Stir, let settle, and add a few drops more of

sodium carbonate solution, and if no fresh precipitate is pro-

duced in the clear part of the solution no more need be added;

otherwise enough more must be added to produce this result.

Filter the solution, hot, through an ordinary filter (Note 4 (c),

o

FIG. 23

page 7). Prepare pure hydrogen chloride by placing 50 grams

of rock salt in the generator flask and treating it with the 95 cc. of

concentrated sulphuric acid. Observe the directions given under

the preparation of hydrochloric acid, page 142, and note par-

ticularly the caution as to the disposal of the hot residue. The

gas is to be purified by bubbling it through the washing bottle

containing about 100 cc. of concentrated hydrochloric acid, and

then it is passed through the wide-mouth funnel into the sodium

chloride solution in the 600-cc. beaker. When hydrogen chloride

ceases to be evolved on heating the generator, collect the pre-