CAUSTIC ALKALIES.

129

Percentage Potash.

Degrees Twaddle.

5*0

10

7-0

14

I0*O

19

12*0

24

14*0

29

16-5

34

IQ'O

40

21*0

45

22*5

5 °

24*0

53

25*0

56

26 0

60

27*0

63

28'0

66

1 c.c. of normal oxalic acid will neutralise 0-047 g rm - of caustic potash.Caustic soda, or hydroxide of sodium, NaHO, occurs in commerce in the

mass or in concentrated solutions.

Fused hydrate of soda is composed in

100 parts of 77-5 parts of anhydrous soda and 22-5 parts of water. It maybe prepared from carbonate solutions by means of caustic lime, or by theignition of a mixture of sulphate of soda, chalk, and small coal, and lixiviatingthe crude soda with water at 50°. The lixivium is concentrated to 1-5 sp. gr.

to deposit carbonate, sulphate of

soda, and sulphide of sodium. The

liquor is kept boiling in iron cauldrons, and Chili saltpetre is then added, inthe proportion of 3 or 4 kilos, of the nitrate to every 100 kilos, of caustic

soda the solution is likely to yield.

During the boiling the nitrate of soda

causes the evolution of ammonia and nitrogen by adting upon the sulphuretand cyanide of sodium present in the solution. Pauli illustrates .the readtion

by the following formula :—•

2NaS + 2NaN0 3 4-4H 2 0 =

2Na 2 S0 4 +2NaH0 + 2HN 3 .

5 Na 2 S + 8NaN03+ 4 H 2 0 =

= 5Na 2 S0 4 +8NaH0 + 8N.

Dalton gives the following table of percentages of caustic soda containedin solutions of the corresponding density:—

Percentage

NaHO.

Specific Gravity.

47

I-o6

9-0

1*12

13-0

x-i8

16-0

1-23

19-0

1-29

23-0

1-32

26-0

1-36

29-0

1-40

31-0

1-44

34 ’°

1-47

36-8

1-50

41-2

1-56

46-6

1-63

53-8

1-72

63-6

1*85

77 'S

2*00

K