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

134 CARBONATES.

as possible in the following manner: Dissolve 0.3 g. of the salt in a

beaker with 10 c.c. of 0.1-normal ferrous ammonium sulphate

1

solution and 200 c.c. of hot water. After cooling, titrate back the

unoxidized ferrous salt with 0.1-normal permanganate.

According to the above directions, 1.25 g. of the persulphate of

92 to 95% purity should be obtained in 40 minutes and 1.65 g. in

an hour, and the current yield should be from 41 to 43%.

To test qualitatively the oxidizing power of the salt, dissolve

some of it in water, make the solution alkaline, add it to a solution

of a lead or manganese salt to which alkali has also been added,

and heat the mixture.

(/) Carbonates.

95. Sodium Carbonate (Ammonia-Soda Process).
    From a concentrated solution containing the ions Na+, Cl~, NH 4 +, and
    HC03~, sodium bicarbonate, NaHC0 3 , the most insoluble of the possible
    salts, is the first to separate (cf. No. 80). 100 grams of saturated aqueous
    solutions of the four salts that come into consideration contain the following
    weights of anhydrous salt in grams.
    15° 30°
    NaCl 26.4 26.5
    NH4HCO3 15.7 21.3
    NH4CI 26.1 29.3
    NaHCO 3 8.1 9.9
    The dry acid salt loses carbon dioxide when heated and changes into the mono-
    carbonate, Na2CO 3. This process, which was first placed on a commercial
    basis by Solvay, yields at the present time the largest part of the world's soda.
    For a technical discussion of the process, consult Ost, Lehrbuch der technischen
    Chemie; for a theoretical treatment in the light of the phase rule, see Bod-
    lander and Breull, Z. angew. Chem. 14, 381, 405 (1901); and P. P. Fedotieff,
    Z; physikal. Chem. 49, 162 (1904).

Add 60 g. of pulverized sodium chloride to 180 g. of a 10%

ammonia solution, and allow it to stand with occasional shaking

until nearly all has dissolved. Place the filtered solution in a closed

flask and saturate it at room temperature with carbon dioxide; pass

the gas through a wash bottle containing water and then allow it

to enter the flask through a single inlet tube, which dips under

the solution, as rapidly as it will be absorbed (in all, perhaps 24

hours).

2

Collect the precipitated sodium bicarbonate on a filter

(^1) 40 g. of (NH^SOi • FeSO
4 • 6 H 2 O and 30 g. of cone. H 2 SO 4 made up to
1 liter and standardized against 0.1-normal permanganate.
(^2) The time taken for the absorption may be reduced to one-half hour if a
2 liter flask is used and it is shaken vigorously throughout the absorption.